| Literature DB >> 34662148 |
Samuel Asare1, Anuja Majmundar1, Farhad Islami2, Priti Bandi3, Stacey Fedewa3, Lee J Westmaas4, Nigar Nargis1.
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Year: 2021 PMID: 34662148 PMCID: PMC8554710 DOI: 10.7326/M21-3350
Source DB: PubMed Journal: Ann Intern Med ISSN: 0003-4819 Impact factor: 25.391
Figure 1.Observed and expected monthly cigarette sales per capita (packs) from March 2020 to June 2021.
The expected sales were based on the interrupted time series equation: Y = β 0 + β 1 T + β 2 X + β X × T + ϕ Z + γ + ξ, where Y = per capita monthly cigarette sales in packs; X = an indicator variable taking the value 0 before the onset of the COVID-19 pandemic and 1 from March 2020 to June 2021; T = linear monthly time trend in cigarette sales, which takes 0 starting from January 2007 and increases by 1 every successive month; Z = a vector of covariates adjusted for in the model (composition of age, sex, race, Consumer Price Index for alcohol and tobacco products, real per capita personal disposable income, and unemployment rate); and γ = a vector of calendar month fixed effects, which included 11 dummies, 1 for each month from February to December, and omitted January as the reference month. The coefficients β 1 = trend in cigarette sales before the onset of the COVID-19 pandemic, β 2 = change in the level of cigarette sales immediately after the onset of the pandemic, and β 3 = change in the trend in cigarette sales after the onset of the pandemic. Data on the composition of age, sex, and race were sourced from the Basic Monthly Current Population Survey of the U.S. Census Bureau. The unemployment rates and Consumer Price Index for alcohol and tobacco products were sourced from the U.S. Bureau of Labor Statistics. The real per capita personal disposable income was sourced from the economic data of the Federal Reserve Bank of St. Louis. The expected sales were predicted on the basis of the pre–COVID-19 estimated trend (January 2007 to February 2020).
Figure 2.Mean difference between observed and expected monthly cigarette sales per capita.
The point estimates (circles) with 95% CIs (error bars) are the average difference between the observed and expected monthly cigarette sales per capita based on the pre–COVID-19 trend. The average difference between the observed and expected monthly cigarette sales per capita was expressed as a count of packs in the top panel and a percentage change from the expected sales in the bottom panel. In each panel, we showed the difference between the observed and expected sales from 5 model specifications, all adjusting for seasonality by including 11 calendar month dummies (January as a baseline). Model specification A adjusted for all of the covariates (composition of age, sex, race, Consumer Price Index for alcohol and tobacco products, real per capita personal disposable income, and unemployment rate); model specification B did not adjust for any covariate; model specification C adjusted for only the composition of age, sex, and race; model specification D adjusted for Consumer Price Index for alcohol and tobacco products, real per capita personal disposable income, and unemployment rate; and model specification E used a 1-month lag of cigarette sales as the dependent variable and adjusted for all of the covariates in model specification A. Ramsey RESET test using Stata command ovtest showed that only model specification A is free from the omitted variable bias.