Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: The Healthy Diné Nation Act of 2014.

INTRODUCTION: In 2014, the Navajo Nation Healthy Diné Nation Act (HDNA) was passed, combining a 2% tax on foods of 'minimal-to-no-nutritional value' and waiver of 5% sales tax on healthy foods, the first-ever such tax in the U.S. and globally among a sovereign tribal nation. The aim of this study was to measure changes in pricing and food availability in stores on the Navajo Nation following the implementation of the HDNA.
METHODS: Store observations were conducted in 2013 and 2019 using the Nutrition Environment Measurement Survey-Stores (NEMS-S) adapted for the Navajo Nation. Observations included store location, type, whether healthy foods or HDNA were promoted, and availability and pricing of fresh fruits and vegetables, canned items, beverages, water, snacks and traditional foods. Differences between 2013 and 2019 and by store type and location were tested.
RESULTS: The matched sample included 71 stores (51 in the Navajo Nation and 20 in border towns). In 2019, fresh produce was available in the majority of Navajo stores, with 71% selling at least 3 types of fruit and 65% selling at least 3 types of vegetables. Compared with border town convenience stores, Navajo convenience stores had greater availability of fresh vegetables and comparable availability of fresh fruit in 2019. The average cost per item of fresh fruit decreased by 13% in Navajo stores (from $0.88 to $0.76) and increased in border stores (from $0.63 to $0.73), resulting in comparable prices in Navajo and border stores in 2019. While more Navajo stores offered mutton, blue corn and wild plants in 2019 compared to 2013, these changes were not statistically significant. DISCUSSION: The findings suggest modest improvements in the Navajo store environment and high availability of fruits and vegetables. Navajo stores play an important role in the local food system and provide access to local, healthy foods for individuals living in this rural, tribal community.

Introduction

The Navajo Nation is one of the largest tribal nations in the United States and worldwide, both in terms of enrollment and geographic area [1,2]. Traditionally, the Navajo people lived a healthy lifestyle characterized by physical activity and consumption of healthy, traditional foods. However, a combination of poverty [1], inadequate and discriminatory policies and disruptions in food systems [3] have led to high rates of food insecurity [4] and nutrition-related chronic diseases such as type 2 diabetes [5,6]. Currently, similar to many American Indian/Alaskan Native (AI/AN) people, the Navajo experience limited access to healthy foods.

Across the Navajo Nation, an area approximately the size of West Virginia, there are only 13 grocery stores, resulting in the area being labeled a ‘food desert’ [7]. There are a larger number of convenience stores, but prior research suggests that convenience stores on and around the Navajo Nation offer more processed foods with minimal nutritional value and at higher prices compared to grocery stores in border towns around the Navajo Nation [8,9]. Proximity, cost and product shelf-life have also been documented as key factors impacting Navajo families’ healthy food purchasing [10,11]. Navajo store managers have demonstrated interest in offering healthier options, but barriers include limited fruit and vegetable choices from distributors and concerns about perceived low customer demand for healthier items [12].

To promote the health of the Navajo people and increase access to healthy foods, the Healthy Diné Nation Act (HDNA) was passed in November 2014, which included a 2% added surtax on unhealthy foods such as baked goods, chips, sugar-sweetened beverages and candy applied at the point-of-sale at the register (not reflected in shelf prices). Passed earlier in 2014 [13]), part of the HDNA also included a waiver of conventional sales tax (at that time 5%, currently 6%) on healthy foods including water, fresh fruits and vegetables and nuts [14]. While several large municipalities in the U.S. (such as Berkeley and Philadelphia [15,16]) have sweetened beverage taxes and international examples exist of unhealthy food taxes [17-21], the HDNA is the first-ever tax on unhealthy foods in the U.S. and any tribal or indigenous nation worldwide with a rural population at high-risk for common chronic diseases.

However, to date, no study has assessed changes in the store food environment after implementation of the HDNA legislation in 2014. Using a follow-up of a validated store survey originally implemented in 2013, this study assessed changes in pricing and availability of healthy and unhealthy foods across Navajo Nation stores from 2013 to 2019. Because the 2013 survey also sampled stores located in border towns adjacent to the Navajo Nation, we sought to compare trends over the past six years on and off the reservation in order to determine whether HDNA could be influencing changes, including increases or decreases in availability and pricing of healthy and less healthy foods.

Methods

Store selection

This was an observational study with repeated measurements compared across two time points: 2013 and 2019. In 2013, a survey called Epi-Aid was conducted to assess the Navajo food store environment [9]. The total Epi-Aid sample in 2013 included 83 stores, of which 63 were on the Navajo Nation (13 grocery, 50 convenience stores) and 20 stores in five border towns. Data on stores was selected from a national proprietary InfoUSA dataset of businesses [22], augmented with information from the Yellow Pages, Google Maps and local residents. Stores were selected if they were accessible via paved roads, and included both chain and independent grocery and convenience stores (including trading posts) and farmers’ markets on the Navajo Nation [23].

The 2013 list was updated using the same databases and calling each chapter on the Navajo Nation within specified intervals (annually) to confirm existing and add new store information. This updated 2019 list was utilized to conduct a follow-up survey in 2019 among all stores from the 2013 study that were still operational. If original stores could not be surveyed, we used a computer-generated randomized algorithm to match the original store to an operational store based on store type (convenience store/grocery store), location (on/off reservation), and region/border town.

Measures

General store information was recorded including geographic location, type of store (grocery or convenience), whether the store accepted Women Infants and Children (WIC) or Supplemental Nutrition Assistance Program (SNAP) benefits, presence of signage promoting healthy foods, unhealthy foods, and/or the HDNA law, and presence of a store snack shop or mini-concession stand. These were defined as additional venues located in a grocery or convenience store where on-the-go foods for immediate consumption such as corn dogs or nachos were sold.

The Nutrition Environment Measurement Survey-Stores (NEMS-S) [24,25] was used to assess food pricing and availability. The NEMS is a validated observation tool developed to assess the nutrition environment in community food and retail outlets including stores [24]. The instrument was adapted in 2013 to include commonly sold foods (including traditional foods such as blue corn meal, soft corn tortillas, mutton, squash). Additional items added to the original survey tool were adapted from the Nemours Healthy Vending Guide [26] to further facilitate assessing the availability of healthy and less healthy snacks within stores.

Procedures

Surveyors participated in a formal day of in-person training led by one of the lead investigators, and included training on the NEMS-S store assessment survey and general information about troubleshooting. Procedures followed were the same for both the 2013 and 2019 observations to allow for comparisons. First, verbal approval to conduct store assessments and store manager surveys was obtained prior to any observation. Once approval was obtained, a surveyor entered the store and observed the food environment, including the signage, displays, foods offered and recorded pricing. Pricing was based on shelf price and did not include sales tax. Additional clarification was asked as needed (e.g., “does your store accept SNAP or WIC?”).

A standard protocol included information on availability and pricing of major food categories of fresh fruits and vegetables, canned items, meat, beverages, water, flour/tortilla/bread, chips and other snacks. Within each category, specific items were assessed (i.e. apples, bananas and oranges under fruits) and the number of items were recorded (ranging from 0 to 6 or more). If multiple brands of an item were available, the surveyor was asked to record the brand with the lowest price and record the size. Surveyors were asked to also find the lowest priced entrée item for a healthy and for a less healthy version, if foods for immediate consumption were available at the store. In the original 2013 Epi-Aid study, healthy or unhealthy classifications were based on the original NEMS or Nemours protocols [24,26], the 2010 Dietary Guidelines for Americans [27] or the USDA Nutrient database [28]. Based on this classification, the number of unhealthy and healthy foods were tabulated and an overall healthy to unhealthy ratio was calculated by dividing the number of foods in each group. All study procedures, measures were approved by the Navajo Nation Human Research Review board under protocol NNR-17.284.

Analyses

Data were collected on printed surveys and then entered using Epi-Info software in 2013 [29]. In 2019, data were entered into an open-source application, CommCare on Samsung GalaxyTM Tablets (Suwon, Gyeonggi-do, South Korea). Study entry quality checks showed an error rate of less than 1%. Analyses included descriptive statistics and frequency distributions using RStudio Version 1.2 (RStudio Inc., Boston, MA) to characterize food availability, including the number and variety of healthy food options and traditional foods, pricing of healthful and unhealthful options (and ratio of the two) and acceptance of WIC or SNAP benefits (yes/no), promotion of local, organic or (un)healthy options (yes or no) and if the store demonstrated it implemented the HDNA legislation. These were calculated and averaged across all stores, and stratified by regional agency, type of store (convenience or grocery store) and location (on and off the Navajo Nation). Because traditional foods were only reported for the Navajo Nation stores in 2013, we report changes in traditional foods’ availability from 2013 to 2019 only for the Navajo Nation stores. Pricing was adjusted for inflation to reflect changes in 2013 dollars using the Consumer Price Index as described by USAID [30]. For produce prices, grocery stores generally sold produce per pound and convenience stores per item. If a store offered both, we recorded the price per pound only as the cheapest price per unit. Since prices per pound and per piece cannot be directly compared, the changes from 2013 to 2019 are compared separately for cost per piece and per pound. Chi-square tests were used for hypothesis testing with categorical variables and t-tests for continuous variables to test whether food availability significantly changed from 2013 to 2019, using a p-value of 0.05. To assess significance of the difference-in-difference, changes in Navajo versus border stores over time, we built regression models, with time (2013 or 2019), location (Navajo Nation vs Border town), and an interaction term (Time*Location).

Results

Store sample

Of the original 83 stores from the Epi-Aid 2013 survey, 51 were successfully surveyed in 2019. The remaining 32 original stores could not be surveyed because they were no longer open (11), their store manager declined participation or needed corporate approval (15) or they could not be matched with the original database because either geocodes, region ID and/or store name were not available (6). Of the stores that could not be surveyed, a total of 88% of these stores were on the Navajo Nation (similar to the overall sample), 81% were convenience stores, 16% grocery stores and 3% other. For these 32 stores, we successfully matched 20 original stores to an operational store for 2019 sampling (see ). The total analytic sample included 71 stores, including 51 original stores and 20 matched pairs, representing all five regions of the Navajo Nation.

Store characteristics

Of the 71 stores in the final analytic sample, a total of 72% of stores were located on the Navajo Nation (n = 51, of which 39 were convenience stores and 12 grocery stores) (see Table 1). Three quarters of all stores had additional venues for immediate or to-go consumption foods (snack shops or mini-concession stands) but only 16% of snack shops sold fruits or vegetables. Over half of stores (55%) accepted WIC and over three-quarters accepted SNAP in both 2013 and 2019. Grocery stores were significantly more likely to accept WIC (94%) compared with convenience stores (37%) (p = 0.001).

Table 1

Store characteristics of Navajo and border town stores, n = 71.

	Matched Sample (n = 71)
Store type	N (%)
Convenience stores	51 (72%)
Grocery stores	20 (28%)
Store Location
Navajo Nation	51 (72%)
Border town	20 (28%)
Region
Southern	7 (10%)
Eastern	4 (6%)
Northern	12 (17%)
Central	5 (7%)
Western	18 (25%)
Southwest	5 (7%)
Border town
Gallup	5 (7%)
Grants	3 (4%)
Farmington	5 (7%)
Flagstaff	3 (4%)
Winslow	4 (6%)
Benefits
Accepts WIC	39 (55%)
Accepts SNAP	57 (80%)
Ready to eat options
Snack shop	53 (75%)
Salad Bar	7 (10%)

Availability of healthier foods

In 2019, the vast majority of stores had fruit for sale, and more than half of stores had vegetables for sale. In 2013, Navajo stores were more likely to sell fresh produce compared with compared with stores located in border towns: 82% of Navajo stores v. 65% of border town stores sold fruits (p = 0.21) and 88% of Navajo stores v. 60% of border town stores sold vegetables (p = 0.018). Between 2013 and 2019, border town stores began increasing their offerings of fresh produce, such that there were no significant differences in produce availability among Navajo versus border town stores in 2019. A total of 82% of Navajo stores and 80% of border town stores sold fruit (p = 1.0), while 78% of Navajo stores and 70% of border town stores sold vegetables (p = 0.66). Among the 9 fresh produce items evaluated (see S1 Appendix), seven of these (apples, oranges, tomatoes, corn, celery, lettuce, and potatoes) were more frequently offered in Navajo stores than border town stores, although this comparison was statistically significant different for only one item, potatoes (p = 0.04).

These findings appear to be largely driven by trends happening in the border town convenience stores over time (see Table 2). In 2013, Navajo convenience stores were more likely to sell fresh fruits (p = 0.052) and fresh vegetables (p = 0.002) than border town convenience stores. By 2019, border town convenience stores had “caught up” to Navajo convenience stores in terms of fruit offerings. As for vegetables, even in 2019, the variety of fresh vegetables offered at Navajo convenience stores still exceeded those at border convenience stores; for example 62% of Navajo convenience stores offered at least three types of vegetables, compared with 17% of border town convenience stores (p = 0.017).

Table 2

Percentage of convenience stores offering healthier items in 2013 and 2019, n = 51.

	2013			2019
	Navajo convenience stores (N = 39) n (%)	Border convenience stores (N = 8) n (%)	P-value*	Navajo convenience stores (N = 39) n (%)	Border convenience stores (N = 8) n (%)	P-value*
Any fruit	30 (77%)	5 (42%)	0.052	30 (77%)	8 (67%)	0.738
≥3 types of fruit	21 (54%)	2 (17%)	0.053	23 (59%)	6 (50%)	0.829
Apples	27 (69%)	4 (33%)	0.059	29 (74%)	6 (50%)	0.116
Oranges	25 (64%)	2 (18%)	0.018	26 (67%)	5 (42%)	0.141
Bananas	19 (50%)	5 (42%)	0.863	19 (49%)	7 (58%)	0.228
Any vegetables	33 (85%)	4 (33%)	0.002	28 (72%)	6 (50%)	0.294
≥3 types of vegetables	25 (64%)	4 (33%)	0.121	24 (62%)	2 (17%)	0.017
Tomatoes	20 (51%)	4 (33%)	0.448	21 (54%)	2 (17%)	0.023
Corn	0	0		3 (8%)	0
Celery	9 (23%)	1 (8%)	0.478	15 (39%)	0	0.035
Lettuce	25 (64%)	4 (33%)	0.121	18 (46%)	2 (17%)	0.113
Potatoes	26 (67%)	3 (25%)	0.027	21 (54%)	1 (8%)	0.005
Squash	2 (5%)	1 (8%)	1	3 (8%)	0	0.513

* P-values comparing convenience stores on the Navajo Nation to border towns.

Availability of traditional foods

From 2013 to 2019, the number of stores that offered any traditional food (blue corn, yellow corn, mutton, wild animals or wild plants) remained nearly constant at 29 stores in 2013 and 30 stores in 2019, though what stores offered changed over time. All Navajo grocery stores and 16 (41%) Navajo convenience stores sampled in 2019 sold traditional foods. As shown in , the availability of mutton (p = 0.154), blue corn (p = 0.492) and wild plants and berries (p = 0.476) increased over time in both grocery and convenience stores and the availability of yellow corn (p = 0.067) decreased but none of these changes were significant. At both time points, grocery stores were more likely to carry traditional foods than convenience stores on the Navajo Nation (p<0.001).

Pricing

The average cost per item of fruit was higher in 2013 on the Navajo Nation compared with those sold in border town stores ($0.88 vs $0.63, p = 0.06). From 2013 to 2019, after adjusting for inflation, the average cost per item of fruit decreased by 13% in stores on the Navajo Nation (from $0.88 to $0.76, p = 0.029- comparing average cost of fruit in 2013 vs 2019 in NN stores) and increased from $0.63 to $0.73 in border stores (p = 0.519- comparing average cost of fruit in 2013 versus 2019 in border stores) (see Table 3). As a result, the cost of fresh fruits on Navajo versus border stores were much more comparable in 2019, compared with 2013. While data on vegetable prices were sparse, they did not change significantly during this period in either region.

Table 3

Inflation-adjusted average price per item among convenience stores, n = 51.

	Average price per item, Navajo Nation stores (n = 39)			Average price per item, Border town stores (n = 12)
	2013	2019	p-value*	2013	2019	p-value*
Fresh fruit
Apples	$1.01 (n = 24)	$0.80 (n = 29)	0.007	$0.87 (n = 4)	$0.83 (n = 6)	0.871
Oranges	$0.90 (n = 23)	$0.83 (n = 25)	0.574	**	$0.83 (n = 5)	N/A
Bananas	$0.72 (n = 22)	$0.59 (n = 21)	0.306	$0.45 (n = 5)	$0.58 (n = 7)	0.505
Average price	$0.88 (n = 69)	$0.76 (n = 75)	0.029	$0.63 (n = 9)	$0.73 (n = 18)	0.519
Fresh vegetables
Celery	$2.29 (n = 6)	$2.51 (n = 18)	0.945	**	**	N/A
Lettuce	$2.04 (n = 25)	$2.14 (n = 24)	0.509	$1.54 (n = 4)	$1.72 (n = 3)	0.710
Potato (per pound)	$0.51 (n = 19)	$0.58 (n = 18)	0.493	**	$0.52 (n = 9)	N/A

In terms of other foods and beverages (see S2 Appendix), the price of water was slightly lower in 2019 ($0.99 per gallon) compared to 2013 ($1.04 per gallon) in Navajo grocery stores (4.8% decrease) and $1.71 to $1.52 in Navajo convenience stores (11.1% decrease); however, border grocery and convenience stores saw similar declines. In 2013, the price of 100% juice was much higher in Navajo grocery stores ($3.92 per 59oz) relative to border grocery stores ($2.94 per 59oz), but much closer in 2019 ($3.04 and $2.87). During the same time, changes in pricing of chips, juice drinks and soda were inconsistent. For example, the price of a 10oz bag of Lays’ chips increased in Navajo grocery stores from $3.23 to $3.63 but decreased in border grocery stores from $3.31 to $2.85, whereas the pattern was the opposite for convenience stores (decrease on the Navajo Nation, increase in border convenience stores).

Health promotion

Among Navajo stores, signage promoting locally grown or organic items did not change, while the promotion of organic items in border town stores did increase over time (see Table 4). The vast majority of stores (>80%) did not identify or promote locally grown or organic items. Both on and off the reservation, signage promoting both healthy and less healthy eating increased. While not a requirement for any store, three stores on the Navajo Nation had promotional signs or other information (i.e. flyers) showing that they implemented the Healthy Diné Nation Act (HDNA) in 2019.

Table 4

Changes in promotion and signage among Navajo and border town stores, n = 71.

	2013			2019			Change
	Navajo stores (n = 51)	Border town stores (n = 20)	p-value	Navajo stores (n = 51)	Border town stores (n = 20)	p-value	Navajo stores	Border town stores	p-value
Promotion of locally grown items	18%	30%	0.410	14%	25%	0.431	-4%	-5%	0.959
Promotion of organic items	6%	25%	0.061	8%	40%	0.004	2%	15%	0.714
Signage promoting healthy eating	22%	30%	0.660	39%	40%	1.00	17%	10%	0.626
Signage promoting less healthy eating	28%	40%	0.457	46%	60%	0.427	18%	20%	0.999
Signage promoting HDNA	0%	0%	N/A	6%	0	0.651	6%	N/A	N/A

*P-values comparing stores on the Navajo Nation to border towns in 2013, 2019 and difference-in-difference/change over time.

Sensitivity analysis

A sensitivity analysis limited to only stores which were successfully measured in 2013 and 2019 (n = 51) yielded very similar findings to those of the full cohort (n = 71). Average absolute pricing difference between the exact matched sample and full cohort was 3.1 cents (some were higher and some lower, and the summed averaged difference was only 0.4 cents). The largest item difference in 2019 was for celery, which was $1.81 per pound in the full cohort and $1.93 in the exact matched sample, a $0.12 difference. The same comparisons were significant in the exact matched sample as in the full cohort.

Discussion

This study presents the first assessment of changes in the food environment following the implementation of the Healthy Diné Nation Act of 2014 (HDNA), which included a 2% tax on unhealthy foods and waived 5% sales tax on healthy items. The HDNA was the first-ever such legislation among an indigenous or rural community at high risk for diabetes and other conditions. Among a broad sample of 51 stores on the Navajo Nation, findings reveal high overall availability of healthy items and modest improvements in the Navajo food store environment. Notably, 71% of Navajo stores offered 3 or more varieties of fruit and 65% sold 3 or more different vegetables. Promotion of healthy eating increased by 18%, and more stores offered traditional foods in 2019 compared with 2013. While not a requirement in the legislation, several stores had signage promoting the HDNA legislation itself, showing their desire to communicate or advertise the legislation to their consumers. In addition, in 2019 cost of fruits was about 17% lower than in 2013, with similar decreases in 100% juice and water.

Despite diet-related disparities in rural communities, very little research has focused on the food store environment in rural areas. For example, in a recent review of factors that influence food store manager decision making regarding healthy food promotion and environmental modification, only 7 of the 31 studies were in rural settings [31]. The review indicated that challenges in rural areas include a shrinking consumer base [32] and reduced demand for produce in summer due to gardening [33], while partnerships with local farmers were cited as a facilitator [34]. However, none of these studies reviewed food store environment changes following a policy like the HDNA. Our study included data from border town stores in order to explore whether any changes in the store environment were unique to the Navajo Nation. We did not identify major consistent differences in trends in pricing or availability between Navajo versus border towns. However, Navajo stores did see a larger decrease in pricing of fruit and 100% juice, bringing their pricing more in line with border towns. While changes cannot be directly linked to the HDNA, these price improvements, combined with greater availability of traditional foods, and increased health promotion signage reflect a trend toward healthier food environments in Navajo store over the six-year period.

Prior research has suggested that following taxation of unhealthy foods, consumption of unhealthy foods decreased, especially among low-income populations [17-21,35]. However, in Mexico, effects of sugar-sweetened beverage taxation were less pronounced in rural areas as the cost of the tax was not entirely passed on to the consumers, defined as a population of less than 2,500 [20-21], similar to the Navajo Nation where the average community size is 1,650 residents [1]. While compliance with HDNA legislation is not fully known at this time and pricing changes may be inconsistent, HDNA revenue has decreased approximately 3% each year, suggesting lower consumption of unhealthy foods or shifting purchases of these items to border towns [35]. Further study is needed to assess whether improvements in the food store environment could moderate or amplify the influence of HDNA on purchasing behavior.

In comparing convenience store trends on the Navajo Nation with those in neighboring towns, some interesting findings emerged. In 2013, more Navajo convenience stores offered fresh produce compared with border town stores. By 2019, while border town convenience stores had reached comparable levels of fresh fruit availability, Navajo convenience stores still exceeded fresh produce availability than border convenience stores in 2019. These findings may reflect the important role of many small stores–including trading posts–on the Navajo Nation: access points for “non-snack” staple foods for the local community. In fact, in a 2019 survey of shoppers exiting small stores on the Navajo Nation, most consumers (72%) reported shopping at that store at least weekly and most (76%) also lived within 30 minutes from the store [36]. In light of the expansive rural geography and paucity of grocery stores on the Navajo Nation, the promising trends toward affordable produce and more traditional foods suggest that small stores could play an important role in reducing food insecurity on the reservation.

Pricing trends among vegetables and other healthy foods were inconsistent, and promotion of local or organic foods was still low. These findings suggest further opportunities for additional health promotion in the Navajo Nation food store environments. Research has already documented that the store managers are interested in providing healthier options [12], and interventions such as placing produce at the point-of-sale, providing culturally appropriate promotional materials, staff training on produce handling and reimbursement for fruit and vegetable vouchers for high-risk families merit further exploration [36-38].

Limitations

The current study has several limitations. First, there are natural sample size limitations due to the number of stores on the Navajo Nation, limiting statistical power in several comparisons. For example, there are only 13 grocery stores on the Navajo Nation and they were all surveyed in both 2013 and 2019. Second, not all stores could be surveyed in 2019 and the matching approach that ensured 20 stores without a direct match were the same type, location (on/off reservation) and region/border town has limitations. However, the sensitivity analysis limited to only stores which were successfully measured in 2013 and 2019 (n = 51) yielded similar findings to those of the full cohort (n = 71). Third, pricing data was based on marked shelf prices, not purchases. While these procedures were the same as in 2013 and no shelf prices were missing, item cost can potentially be marked incorrectly and sales tax including the HDNA was not included in the price. Further, the 2013 and 2019 data present snapshots of the cost and availability of foods at one time-point, rather than documenting price fluctuations over time. However, data collection occurred in the same season in both 2013 and 2019, in an effort to limit the effect of any seasonal impact on pricing and availability. Finally, while increases in health promotion and direct signage about the HDNA suggest some increased awareness, the extent to which the HDNA legislation may have spurred any changes requires further study; in-depth interviews with store managers would be needed to gain further insight into underlying barriers and facilitators of healthy changes, HDNA implementation and promotion in the food store environment.

Conclusions

This was the first study to assess changes in the Navajo Nation food store environment following implementation of the Navajo Nation legislation combining a 2% tax on unhealthy foods with a waiver of 5% sales tax on healthy foods. Although not necessarily linked to HDNA, we observed improvements in pricing and varieties of healthy produce, primarily in Navajo convenience stores. Due to the low density of grocery stores, convenience stores play a major role in the food availability and modest improvements have the potential to impact food accessibility for rural tribal communities at high-risk for food insecurity and food-related chronic conditions.

Percentage of Navajo and border town stores offering healthier items in 2013 and 2019, n = 71.

(DOCX)

Click here for additional data file.

Inflation-adjusted average price of food items in Navajo and border town grocery and convenience stores, 2013 and 2019.

(DOCX)

Click here for additional data file.

23 Apr 2021

PONE-D-21-08279

Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: the Healthy Diné Nation Act of 2014

PLOS ONE

Dear Dr. Shin,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please focus in particular on the comments related to the gap identified in the introduction and including some methodologic details regarding the border towns and display of prices on the shelves.

Please submit your revised manuscript by Jun 07 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Maya K. Vadiveloo

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

3. We note that you have indicated that data from this study are available upon request. PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly. For information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions.

In your revised cover letter, please address the following prompts:

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories.

We will update your Data Availability statement on your behalf to reflect the information you provide.

4. We note that Figure 2 in your submission contain map images which may be copyrighted. All PLOS content is published under the Creative Commons Attribution License (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For these reasons, we cannot publish previously copyrighted maps or satellite images created using proprietary data, such as Google software (Google Maps, Street View, and Earth). For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright.

We require you to either (1) present written permission from the copyright holder to publish these figures specifically under the CC BY 4.0 license, or (2) remove the figures from your submission:

You may seek permission from the original copyright holder of Figure 2 to publish the content specifically under the CC BY 4.0 license.

We recommend that you contact the original copyright holder with the Content Permission Form (http://journals.plos.org/plosone/s/file?id=7c09/content-permission-form.pdf) and the following text:

“I request permission for the open-access journal PLOS ONE to publish XXX under the Creative Commons Attribution License (CCAL) CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). Please be aware that this license allows unrestricted use and distribution, even commercially, by third parties. Please reply and provide explicit written permission to publish XXX under a CC BY license and complete the attached form.”

Please upload the completed Content Permission Form or other proof of granted permissions as an "Other" file with your submission.

In the figure caption of the copyrighted figure, please include the following text: “Reprinted from [ref] under a CC BY license, with permission from [name of publisher], original copyright [original copyright year].”

If you are unable to obtain permission from the original copyright holder to publish these figures under the CC BY 4.0 license or if the copyright holder’s requirements are incompatible with the CC BY 4.0 license, please either i) remove the figure or ii) supply a replacement figure that complies with the CC BY 4.0 license. Please check copyright information on all replacement figures and update the figure caption with source information. If applicable, please specify in the figure caption text when a figure is similar but not identical to the original image and is therefore for illustrative purposes only.

The following resources for replacing copyrighted map figures may be helpful:

USGS National Map Viewer (public domain): http://viewer.nationalmap.gov/viewer/

The Gateway to Astronaut Photography of Earth (public domain): http://eol.jsc.nasa.gov/sseop/clickmap/

Maps at the CIA (public domain): https://www.cia.gov/library/publications/the-world-factbook/index.html and https://www.cia.gov/library/publications/cia-maps-publications/index.html

NASA Earth Observatory (public domain): http://earthobservatory.nasa.gov/

Landsat: http://landsat.visibleearth.nasa.gov/

USGS EROS (Earth Resources Observatory and Science (EROS) Center) (public domain): http://eros.usgs.gov/#

Natural Earth (public domain): http://www.naturalearthdata.com/

5. Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for the opportunity to review this manuscript. As the authors note, no prior studies have assessed changes in the food store environment after the implementation of the HDNA, which is a topic of interest to health researchers and policymakers, among others. The paper is well-written and synthesizes existing research on the subject clearly.

My primary concerns relate to how price data was collected, particularly in convenience stores, in which prices may or may not be listed on the shelf. If they were all posted, then please specify that in the text, and if not, it would be helpful to know from what percentage of stores the prices were obtained from the store owner (or by purchasing the items). Additionally, it is unclear whether the sales tax was included in the prices, which is an important consideration given that this analysis looks at changes in price and the waiver of sales tax on the price of healthy foods is a key component of HDNA. Other, more minor suggestions are described below.

Ln 35: suggest “offered” in place of “sold” for clarity, since data was collected on product availability, and can’t tell us about sales.

Ln 56: “Tribal” is capitalized here, but not elsewhere (e.g., line 80). Suggest using whichever convention is preferred consistently throughout.

Ln 79: Philadelphia’s tax is technically a “sweetened beverage tax”, rather than a sugar-sweetened beverage tax since it applies to artificially sweetened beverages as well. Suggest choosing a different example city or dropping the “sugar-“.

Line 97: add “would” after “healthy foods”

Ln 98: What do you mean by “regional variability”? Did you stratify by region?

Ln 113: Sentence is a bit confusing- was the list updated in 2019 or was it updated annually?

Lns 145-150: Were prices listed on shelf tags (or the products themselves) or were prices obtained by asking the store owner/manager, or a combination? Did you collect data about whether prices were displayed in the store or not?

Also, if prices were listed on the shelf tag, was sales tax included, not included, or was it unknown? I think this is highly relevant given the content of the HDNA law.

Lns 161-164: What do you mean by the number/variety of healthy food options and the ratio of healthful/unhealthful options? Is this based on all items available in the store or a specific set of items from the NEMS tool?

Ln 164: How did stores demonstrate that they had implemented HDNA? Was this measured based on presence of a sign in the stores?

Lns 168-169: This is confusing. Are prices not presented unless the produce item was priced per item? Were they included in the analysis? This seems problematic if grocery stores typically price produce by weight.

Lns 180-181: Was drop-out/closure differential by location (on or off-reservation)? Also, what proportion of stores that dropped out (or closed) were grocery stores?

Ln 199: Sentence should make it clear that the p-value for fruit was non-significant (unless there is a typo).

Ln 210: add “more” before “likely.”

Ln 219: “Bordertown” sounds like a single place when capitalized and in the singular.

Lns 222-3: Is this out of all stores or out of Navajo stores only? Did no bordertown stores sell traditional foods?

Ln 287: “wasn’t” should be “was not.”

Ln 312: It is unclear who “they” are- is this store owners?

Table 2: Add total “Ns” in the header row (e.g., Navajo convenience stores, N=39)

Table 4: Suggest changing the title from “Trends” to “Changes”, since data is from two time points. Also, was there a reason p-values weren’t included for the Navajo store v. border store comparison?

Reviewer #2: Overall thoughts and summary:

The authors’ work is important and novel and merits publication with minor revisions.

Major comment:

• Overall, I was confused about how the authors conceptualized the link between the HDNA legislation and changes in pricing and availability of healthy and unhealthy foods in stores subject to the legislation. My impression after reading the Introduction was that the authors were exploring a potential mechanism for their previous work -- specifically that the food tax likely lead to a decrease in purchasing of unhealthy foods. However, lines 282-283 and 329-331 in the Discussion make me think otherwise. Why do the authors state that “it is not possible to determine whether changes in the food environment were due to the HDNA legislation or other factors”? If the rationale for looking at changes in pricing/availability are NOT related to the food tax, then why make it the focus of the introduction?

Minor comments:

• Can you state earlier, in the methods section, why you are comparing outcomes of interest between the Navajo nation and border towns?

• Line 233: Can you first state that the cost of fresh fruits was higher in Navajo (vs. border) stores at baseline?

• Lines 255-256 and 269-270: Can you comment further on the implications of so few stores demonstrating implementation of the HDNA legislation?

• Lines 324-326: Suggest adding this sensitivity analysis to the methods and results.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

21 Jun 2021

Article title: Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: the Healthy Diné Nation Act of 2014

Responses to reviewer/editorial comments.

Editor comments:

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please focus in particular on the comments related to the gap identified in the introduction and including some methodologic details regarding the border towns and display of prices on the shelves.

Overall Response:

Thank you for these comments and thoughtful review of the manuscript overall. We feel it has been greatly strengthened as a result of the feedback. Notably, we have adjusted the introduction to more appropriately focus on changes in the Navajo Nation food environment and comparison to border town stores added clarification throughout to several methodological issues (and also added these as limitations in the discussion as appropriate). In addition, we have included how pricing data was collected, clarified issues regarding item pricing per piece and per pound, included additional details about the NEMS survey categories and clarified store promotion of the HDNA legislation. Detailed responses to reviewer comments are outlined below.

Reviewer comments:

Reviewer #1: Thank you for the opportunity to review this manuscript. As the authors note, no prior studies have assessed changes in the food store environment after the implementation of the HDNA, which is a topic of interest to health researchers and policymakers, among others. The paper is well-written and synthesizes existing research on the subject clearly.

My primary concerns relate to how price data was collected, particularly in convenience stores, in which prices may or may not be listed on the shelf. If they were all posted, then please specify that in the text, and if not, it would be helpful to know from what percentage of stores the prices were obtained from the store owner (or by purchasing the items).

Response: Thank you for this comment. We have clarified that data collection was based on observational surveys and marked prices, not purchases. If pricing information was missing, store staff was inquired. The primary reason for this approach ¬¬was to follow the same procedures as were implemented as in 2013 to allow for direct comparison in pricing between 2013 and 2019. We have clarified this in the text and also added this as a limitation in the discussion section.

Comment: Additionally, it is unclear whether the sales tax was included in the prices, which is an important consideration given that this analysis looks at changes in price and the waiver of sales tax on the price of healthy foods is a key component of HDNA. Other, more minor suggestions are described below.

Response: Sales tax was not included since the price information was based on marked prices. This has now also been clarified and added as a limitation to the discussion section.

Comment: Ln 35: suggest “offered” in place of “sold” for clarity, since data was collected on product availability, and can’t tell us about sales.

Response: This change was made.

Comment: Ln 56: “Tribal” is capitalized here, but not elsewhere (e.g., line 80). Suggest using whichever convention is preferred consistently throughout.

Response: We made it lowercase to be consistent throughout.

Comment: Ln 79: Philadelphia’s tax is technically a “sweetened beverage tax”, rather than a sugar-sweetened beverage tax since it applies to artificially sweetened beverages as well. Suggest choosing a different example city or dropping the “sugar-“.

Response: Thank you! We dropped the word sugar.

Comment: Line 97: add “would” after “healthy foods”

Response: This change was made. However, we subsequently removed the sentences as we want to be cognizant we are not analyzing sales data.

Comment: Ln 98: What do you mean by “regional variability”? Did you stratify by region?

Response: Apologies this was indeed unclear. We intended to compare the on-reservation to border town changes and have removed the text referring to regional variability (there are 5 regions on the Navajo Nation, but since the HDNA was applied across the entire Navajo Nation, so we did not compare HDNA implementation across Navajo Nation regions).

Comment: Ln 113: Sentence is a bit confusing- was the list updated in 2019 or was it updated annually?

Response: Apologies, this was confusing. The list was updated annually as part of general research team maintenance of the store database. The 2019 update was the list used for the follow-up data collection, which is why we referred to it specifically. We tried to clarify the sentence.

Comment: Lns 145-150: Were prices listed on shelf tags (or the products themselves) or were prices obtained by asking the store owner/manager, or a combination? Did you collect data about whether prices were displayed in the store or not? Also, if prices were listed on the shelf tag, was sales tax included, not included, or was it unknown? I think this is highly relevant given the content of the HDNA law.

Response: This is indeed important context. Prices were based on observational data and shelf prices using the NEMS survey to match the procedures implemented in 2013. Store staff was asked if pricing information was missing (the frequency was not formally recorded, but it was rare). We have aimed to clarify this throughout the manuscript and added this as a limitation.

Comment: Lns 161-164: What do you mean by the number/variety of healthy food options and the ratio of healthful/unhealthful options? Is this based on all items available in the store or a specific set of items from the NEMS tool?

Response: The number and variety of items was indeed based on the NEMS tool, which has 10 sections such as milk, breads & tortillas, fruits & vegetables, meats and hot dogs, canned foods etc. There are subsections under each section for specific individual types of foods; for example, 3 types of fruits and 6 types of vegetables are specifically listed and checked: apples, bananas, oranges, tomatoes, celery, lettuce, corn, squash, potatoes. It was also assessed if healthier versions of certain foods were available (i.e. low fat milk, lean ground beef, 100% juice). In addition, the tool specifies the number of items under each section (for example, for fruits, vegetables, chips etc.), with answer options being 0,1,2,3,4,5 and 6 or more. The data was summarized for the individual foods and the overall number of foods available under each section. Finally, foods were categorized as healthful or unhealthful and the ratio of these was calculated by dividing the total number of available food types in each category. We have added more detail to the methods section to clarify the procedures and ratio.

Comment: Ln 164: How did stores demonstrate that they had implemented HDNA? Was this measured based on presence of a sign in the stores?

Response: Indeed, this was noted based on presence of a sign or other promotional information (flyer etc.) in the store. This has been added to clarify.

Comment: Lns 168-169: This is confusing. Are prices not presented unless the produce item was priced per item? Were they included in the analysis? This seems problematic if grocery stores typically price produce by weight.

Response: Apologies, we agree this was confusing. The NEMS survey indicates to record the price per cheapest unit being sold. If a store offered a type of produce both per-piece and per-pound, only the per-pound price was recorded as it almost always is the cheapest per unit price. Because it is challenging to aggregate data across per-piece or per-pound pricing methods, comparisons between 2013 and 2019 pricing were made separately for per piece and per pound pricing. Indeed, grocery stores typically only sold produce per pound. For example, in the full cohort, 17 stores in 2013 offered apples only per pound and 18 in 2019, and the average price was compared between these stores for the cost of apples per pound. We have attempted to clarify the abovementioned sentences to reflect this approach more clearly.

Comment: Lns 180-181: Was drop-out/closure differential by location (on or off-reservation)? Also, what proportion of stores that dropped out (or closed) were grocery stores?

Response: Of the 32 stores that were closed/declined participation or had missing geocode data, 88% were on the Navajo Nation, 12% in border towns, 81% were convenience stores, 16% grocery stores and 3% other. This information has been added to the manuscript.

Comment: Ln 199: Sentence should make it clear that the p-value for fruit was non-significant (unless there is a typo).

Response: We added the letters ns. to indicate the p-value was indeed not significant. This was incidentally not a typo, as the p-value was 1.0 rounded up as percentages were nearly identical for convenience stores offering fruits on the Navajo Nation (82%) and in bordertowns (80%). We have also added .ns for the other comparisons in the same paragraph that were not statistically significant.

Comment: Ln 210: add “more” before “likely.”

Response: Thank you, this change was made.

Comment: Ln 219: “Bordertown” sounds like a single place when capitalized and in the singular.

Response: We agree and revised this to read: “P-value comparing convenience stores on the Navajo Nation to border towns.”

Comment: Lns 222-3: Is this out of all stores or out of Navajo stores only? Did no bordertown stores sell traditional foods?

Response: Unfortunately traditional foods were only assessed in the Navajo stores in 2013. Thus, we only reported traditional food availability in the Navajo grocery and convenience stores in 2019 as well to facilitate comparability between samples. We have added this clarification to the methods section.

Comment: Ln 287: “wasn’t” should be “was not.”

Response: This change was made.

Comment: Ln 312: It is unclear who “they” are- is this store owners?

Response: Indeed, these are the store managers. This was changed.

Comment: Table 2: Add total “Ns” in the header row (e.g., Navajo convenience stores, N=39)

Response: The N’s were added to the header row.

Comment: Table 4: Suggest changing the title from “Trends” to “Changes”, since data is from two time points. Also, was there a reason p-values weren’t included for the Navajo store v. border store comparison?

Response: We agree and Trends was changed to Changes. P-values were added to Table 4.

Reviewer #2: Overall thoughts and summary:

The authors’ work is important and novel and merits publication with minor revisions.

Major comment:

• Overall, I was confused about how the authors conceptualized the link between the HDNA legislation and changes in pricing and availability of healthy and unhealthy foods in stores subject to the legislation. My impression after reading the Introduction was that the authors were exploring a potential mechanism for their previous work -- specifically that the food tax likely lead to a decrease in purchasing of unhealthy foods. However, lines 282-283 and 329-331 in the Discussion make me think otherwise. Why do the authors state that “it is not possible to determine whether changes in the food environment were due to the HDNA legislation or other factors”? If the rationale for looking at changes in pricing/availability are NOT related to the food tax, then why make it the focus of the introduction?

Response: We agree this was confusing and we have changed the introduction to limit the focus on any reductions in purchasing of unhealthy foods since purchase data are not available, and instead emphasize the focus on changes in the Navajo food store environment between 2013 and 2019 and compared to border towns. Lines 282-283 were removed and lines 329-331 rephrased to indicate that modest improvements (i.e. Navajo store pricing ‘catching up’ with border stores in some cases like fruits and 100% juice, more health promotion, explicit HDNA signage etc.) suggest some extent of increased awareness, but that further study is needed to which extent these were spurred by the HDNA. In-depth interviews with store managers will take place throughout 2021 to gain further insight into these questions.

Minor comments:

Comment: • Can you state earlier, in the methods section, why you are comparing outcomes of interest between the Navajo nation and border towns?

Response: We have now stated this earlier. Our main reason was that border towns are not subject to the HDNA legislation (neither the waiver of sales tax on healthy foods nor the added 2% HDNA tax on unhealthy foods. In addition, food accessibility issues on the Navajo Nation are a key reason behind the work in general and Navajo stores being able to offer similar healthy food options at similar price points to the border towns would be an important step in improving the food environment for the Navajo people.

Comment: • Line 233: Can you first state that the cost of fresh fruits was higher in Navajo (vs. border) stores at baseline?

Response: We have now added this.

Comment: • Lines 255-256 and 269-270: Can you comment further on the implications of so few stores demonstrating implementation of the HDNA legislation?

Response: We have now added language clarifying that these were stores that had promotional signage explicitly showing they were implementing the HDNA. There is no requirement for the stores to advertise the HDNA implementation. As a result, it is possible that store managers simply did not prioritize adding signage or did not want to necessarily advertise they were taxing an additional 2% on unhealthy foods. We are currently conducting interviews with store managers to gain insight into questions such as these about communication of the HDNA to consumers and motivation behind adding promotional signage about the HDNA. We have added this in the text to clarify.

Comment: • Lines 324-326: Suggest adding this sensitivity analysis to the methods and results.

Response: The sensitivity analysis was added to the methods and results section. Notably, results were highly similar: on average, prices were about 3 cents different between the exact matched sample and total sample (some were higher and some lower, when all values were added, average summed difference was 0.4 cents per item). The largest difference for any one item in 2019 was 12 cents for celery per pound ($1.81 in the total cohort, $1.93 in the exact matched sample). The same comparisons were still statistically significant.

Submitted filename: May 20 PlosOne Responses to reviewer comments sss.docx

Click here for additional data file.

28 Jul 2021

PONE-D-21-08279R1

Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: the Healthy Diné Nation Act of 2014

PLOS ONE

Dear Dr. Shin,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Sep 11 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Maya K. Vadiveloo

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Additional Editor Comments (if provided):

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Overall

This is interesting and well-written paper on a topic that has not been published about previously. The authors’ revisions have improved the clarity of the paper, although there are still some remaining issues to be addressed. Most of my suggestions are minor, although there is one methodological question to be considered.

Comments:

Line 30: The word “of” is missing after “the majority.”

Line 35: I suggest revising to say “While more Navajo stores offered traditional foods in 2019 (54%) compared to 2013 (38%), this trend was not statistically significant” to make the comparison clearer.

Lines 73-77: My understanding is that the HDNA is a sales tax, which is applied at the point of purchase. I suggest adding an additional sentence or clause to clarify that the prices of items subject to the HDNA likely do not reflect the price increase due to the tax, which would be applied at the register (if that is correct).

Line 122: Suggest deleting the word “popular.”

Lines 169-171: Most of the comparisons you make are between the Navajo Nation stores and the border town stores at the same time point. I don’t see a problem with that; however, you do in some cases compare the difference in availability or price over time for Navajo Nation stores compared to border town stores in the text (e.g., the abstract & lines 233-235). In most cases, you don’t report on the statistical significance of the change (“The cost of fresh fruit decreased by 18% in Navajo stores, compared with 6% in border stores”), which you may want to consider doing, so that the reader knows if the change is in fact significantly different from zero, and if the change in Navajo stores is statistically significantly different from the change in border stores (difference-in-differences).

Additionally, you report in the abstract that “While more Navajo stores offered traditional foods (38% in 2013 v. 54% in 2019), this trend was not statistically significant.” The section in the paper on traditional food availability does not include statistical tests, so it is not clear how this was compared. Given that you have matched samples, if you are comparing the same group of stores (e.g., Navajo Nation stores) at two time points, I believe you should use a paired t-test for continuous variables (or a non-parametric test like the Wilcoxon signed rank test if the change in price for the item is not normally distributed) and McNemar’s test for binary variables.

Line 179: missing “a” before “total”

Line 189: Suggest adding “all” before “stores” so that it is clear that you are talking about the full sample, not only the Navajo Nations stores. Also, 75% is substantially more than half, so you might re-word to say “Most stores (75%) had additional venues...” or something similar.

Lines 233-235: These lines currently refer the reader to Table 3, which does not show any measure of statistical significance, nor does it display the average cost of fresh fruit overall or the difference in average cost (referenced in the abstract and the lines mentioned).

Table 4 shows the statistical significance of the difference between sign presence in Navajo stores and border towns in 2013 and again in 2019, with a column showing the magnitude of the change over time by store location (on or off reservation), but no statistical measures. The table is also missing a footnote describing what the p-values indicate.

Line 279: The table indicates a difference of 17% for signs promoting healthy eating, not 18%.

Line 299: If prices were measured in the same season in 2013 and 2019, shouldn’t this be a six-year period?

Line 312: Suggest checking for consistency throughout the paper for use of “Navajo Nation” v. “the Navajo Nation.”

Line 321: There is a typo here (“Nation Nation”).

Line 343: Suggest adding “including the HDNA” after “sales tax”, since the HDNA is also a type of sales tax (if this is accurate).

Line 356: Suggest deleting “likely” before “necessarily.”

Line 360: Unclear what high-risk refers to – food security? Diet-related chronic disease?

Reviewer #2: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

10 Aug 2021

Article title: Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: the Healthy Diné Nation Act of 2014

Responses to reviewer/editorial comments.

Editor comments:

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Response: Thank you for the opportunity to further clarify the manuscript and add additional information on statistical significance. We have made the requested revisions and outlined responses to each comment below.

Reviewer #1: Overall

Comment: This is interesting and well-written paper on a topic that has not been published about previously. The authors’ revisions have improved the clarity of the paper, although there are still some remaining issues to be addressed. Most of my suggestions are minor, although there is one methodological question to be considered.

Response: Thank you for your thoughtful and detailed review. We have appreciated the opportunity for additional clarification and believe the manuscript was further refined and improved as a result.

Comments:

Line 30: The word “of” is missing after “the majority.”

Line 35: I suggest revising to say “While more Navajo stores offered traditional foods in 2019 (54%) compared to 2013 (38%), this trend was not statistically significant” to make the comparison clearer.

Response: We agree and have made these revisions.

Comment: Lines 73-77: My understanding is that the HDNA is a sales tax, which is applied at the point of purchase. I suggest adding an additional sentence or clause to clarify that the prices of items subject to the HDNA likely do not reflect the price increase due to the tax, which would be applied at the register (if that is correct).

Response: Indeed, this is correct and a good point of clarification. We have added a sentence to clarify the HDNA tax was applied at the point-of-sale at the register.

Comment: Line 122: Suggest deleting the word “popular.”

Response: The word popular has been removed.

Comment: Lines 169-171: Most of the comparisons you make are between the Navajo Nation stores and the border town stores at the same time point. I don’t see a problem with that; however, you do in some cases compare the difference in availability or price over time for Navajo Nation stores compared to border town stores in the text (e.g., the abstract & lines 233-235). In most cases, you don’t report on the statistical significance of the change (“The cost of fresh fruit decreased by 18% in Navajo stores, compared with 6% in border stores”), which you may want to consider doing, so that the reader knows if the change is in fact significantly different from zero, and if the change in Navajo stores is statistically significantly different from the change in border stores (difference-in-differences).

Additionally, you report in the abstract that “While more Navajo stores offered traditional foods (38% in 2013 v. 54% in 2019), this trend was not statistically significant.” The section in the paper on traditional food availability does not include statistical tests, so it is not clear how this was compared. Given that you have matched samples, if you are comparing the same group of stores (e.g., Navajo Nation stores) at two time points, I believe you should use a paired t-test for continuous variables (or a non-parametric test like the Wilcoxon signed rank test if the change in price for the item is not normally distributed) and McNemar’s test for binary variables.

Response: Thank you for these comments as we feel these analyses add valuable detail to the manuscript regarding statistical significance. For the pricing data, we updated the estimates for change in price and added p-values from the paired t-tests for both Navajo Nation stores and border towns. The initial comparisons averaged price changes for each fruit individually and then averaged the totals (initially, no paired comparison test was conducted). However, this did not take into account differences in sample sizes for individual fruits, so in the updated analyses, we calculated average change in price for all fruits combined (n=69 and n=75 for Navajo stores, n=9 and n=18 for border stores) and conducted t-tests. The updated analyses show a decrease of 13% in overall cost of fruit in Navajo Nation stores, from $0.88 to $0.76, which was significant p=0.029. The average cost in border town stores increased from $0.63 to $0.73, p=.519. Text in the results section and abstract were updated to reflect the changes. We also reformatted Table 3 to include the p-values for the comparison of change in average price between 2013 and 2019 for individual fruits and vegetables and also for average price per item of fruit.

Regarding traditional food availability, we added further detail to provide additional description of the types of traditional foods (blue corn, yellow corn, mutton or wild animals or wild plants) to align with what was presented in Figure 2. The availability of mutton, blue corn and wild plants increased from 2013 to 2019, although changes were not statistically significant. We have replaced the original text with these more detailed analyses and added the p-values for tests of significance for each individual traditional food to the section on traditional foods.

Comment: Line 179: missing “a” before “total”

Response: The ‘a’ was added..

Comment: Line 189: Suggest adding “all” before “stores” so that it is clear that you are talking about the full sample, not only the Navajo Nations stores. Also, 75% is substantially more than half, so you might re-word to say “Most stores (75%) had additional venues...” or something similar.

Response: We agree and this was changed to ‘Three quarters’ of all stores…”

Comment: Lines 233-235: These lines currently refer the reader to Table 3, which does not show any measure of statistical significance, nor does it display the average cost of fresh fruit overall or the difference in average cost (referenced in the abstract and the lines mentioned).

Response: We added the average cost of fresh fruit to the table, updated the abstract and text with this information and added p-values for the specific comparisons mentioned. None of the individual price findings were statistically significant, although the overall cost of fruit decreased significantly in Navajo Nation stores.

Comment: Table 4 shows the statistical significance of the difference between sign presence in Navajo stores and border towns in 2013 and again in 2019, with a column showing the magnitude of the change over time by store location (on or off reservation), but no statistical measures. The table is also missing a footnote describing what the p-values indicate.

Response: We conducted a regression analysis to calculate the difference-in-difference, including a time x location interaction term. The description of the regression analysis was added to the methods section and the p-values for the difference in difference and footnote were added to Table 4.

Comment: Line 279: The table indicates a difference of 17% for signs promoting healthy eating, not 18%.

Response: This was changed.

Comment: Line 299: If prices were measured in the same season in 2013 and 2019, shouldn’t this be a six-year period?

Response: This is correct and this was changed to a six-year period.

Comment: Line 312: Suggest checking for consistency throughout the paper for use of “Navajo Nation” v. “the Navajo Nation.”

Response: We have changed throughout the read the Navajo Nation.

Comment: Line 321: There is a typo here (“Nation Nation”).

Response: Thank you, this was changed.

Comment: Line 343: Suggest adding “including the HDNA” after “sales tax”, since the HDNA is also a type of sales tax (if this is accurate).

Response: Yes, this is correct and was added.

Comment: Line 356: Suggest deleting “likely” before “necessarily.”

Response: This was changed.

Comment: Line 360: Unclear what high-risk refers to – food security? Diet-related chronic disease?

Response: We revised the sentence to indicate that the high risk referred to food insecurity and food-related chronic conditions.

Submitted filename: AUG 9 PlosOne Responses to reviewer comments.docx

Click here for additional data file.

13 Aug 2021

Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: the Healthy Diné Nation Act of 2014

PONE-D-21-08279R2

Dear Dr. Shin,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Maya K. Vadiveloo

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Thank you for your prompt and thoughtful responses to the reviewer feedback.

Reviewers' comments:

25 Aug 2021

PONE-D-21-08279R2

Changes in food pricing and availability on the Navajo Nation following a 2% tax on unhealthy foods: the Healthy Diné Nation Act of 2014

Dear Dr. Shin:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Maya K. Vadiveloo

Academic Editor

PLOS ONE