Measuring and Reducing Chemical Spills by Students: A Randomized Controlled Trial of Providing Feedback.

The ability to handle chemicals safely is a key aspect of the learning development of students studying chemistry; however, there have been no previously reported investigations of the quantity of chemicals spilled by students during lab experiments. Therefore, the first part of this article reports the assessment of the volume of chemicals spilled by year 1 undergraduate chemistry students (n = 64) at a U.K. university during an existing chemical analysis practical designed to develop volumetric handling skills. The experiment was carried out on paper liners, allowing the areas of students' spills to be visible and quantified using calibrated spill volumes of liquid to determine the resultant spill area. The volume spilled by the student group was ca. 1.2% of that handled; however, the amount spilled by individual students ranged widely, from ca. 0.02% to ca. 10% of the volume handled. A feedback tool has been developed to allow laboratory demonstrators to rapidly quantify chemical spillage by individual students. This tool also provides the demonstrators with a framework to communicate the potential safety significance of the volume of chemical a student has spilled. A randomized controlled trial (RCT) was carried out to examine the effect of providing feedback to students on their chemical spillage during a subsequent experiment. From a cohort of 185 year 1 undergraduate students, 150 consented to be randomized (81%), and data was collected for 144 students (96% of those randomized). A Hodges-Lehmann estimator for the median change in volume spilled during the second experiment due to providing feedback on spillage during first experiment was a 50% decrease in volume spilled (95% confidence range: 0 to 80% decrease, Mann-Whitney U test p = 0.05). The RCT was a waiting list trial, with all student receiving feedback either during or after the RCT, with blinded assessment by the demonstrators assessing volume spilled for the RCT.

RCT Entities:   Population Interventions Outcomes

Introduction

Spillage resulting from mishandling of chemicals has the potential to cause harm to people working with chemicals,[1−3] and exposure though accidental spillage and subsequent skin contact can cause a wide range of serious acute or chronic adverse effects,[4] including, in some cases, life-changing or life-threatening harm.[5]

Personal protective equipment (PPE) such as gloves that are acceptably impervious to the chemicals being handled[6] can and should be used; however, the use of PPE is cited at the lower end of hierarchies of control techniques used to manage risk,[7,8] due to limitations of their use. Hence, a preferable approach is to aim at minimizing chemical spillage in the first place.

A key aspect of university chemistry education is that graduating students have demonstrated an ability to handle chemicals safely, and accreditation of chemistry degree courses reflects this in their requirements.[9,10] Assessment of laboratory skills can be done in a variety of ways; however, the specific skill of being able to handle chemicals without significant spillage is typically not explicitly considered. Instead, outcomes such as an ability to obtain a synthesis product in a certain yield or purity, or achievement of a concentration analysis of an acceptable accuracy, are commonly used as a measure of skill in the lab.[11−16]

Two aspects of chemical spillage by students are reported here: (1) the development of a simple technique for assessing chemical spillage by individual students during laboratories, and (2) the design of a tool for demonstrators to allow them to provide formative feedback to the students on the potential consequences of the volume of chemicals they have spilled.

Using this measurement technique and feedback tool, a randomized controlled trial (RCT) design was used to assess whether providing feedback to students on the volume of chemicals they have spilled has an effect on the volume they subsequently spill.

Preliminary Investigation of Chemical Spillage by Students

Student Concentration Determination Experiment

The year 1 chemistry undergraduate students in this study undertake a spectroscopy experiment in their first term to develop their volumetric handling skills; chemical spillage by the students during this experiment is reported here. The students were each randomly assigned two colored copper(II) compounds from four possibilities; copper(II) sulfate, copper(II) chloride, copper(II) nitrate, or copper(II) acetate. For each of the selected chemicals, they prepared a 50 cm3 aqueous stock solution of 0.1 M concentration (or 0.05 M for copper(II) acetate). The hazards of the chemicals used have no chronic toxicity listed in their safety data sheets, and they show comparatively low acute toxicity (e.g., Acute toxicity, Oral (Category 4)).[17,18] Scanning UV–vis spectrometry was used to determine the wavelength of maximum absorption, λmax, of the solution, and four dilutions with a range of concentrations were then prepared by the student from their stock solution. The absorbance at λmax was determined for each concentration. The molar absorption coefficient, determined from the absorbance vs concentration graphs for their calibration samples, was then used to determine the concentration of unknown samples for each of the two chemicals. In total, the volume of liquid handled by each student throughout the day-long experiment (that could give a color if spilled) was approximately 200 cm3 (the students had some discretion in what volumes and dilutions to use), handling ca. 100 cm3 for each of the copper compounds, with one examined in the morning session and the second in the afternoon. The experiment script for the students is available in the Supporing Information.

Quantification of Chemical Spillage During Analysis Experiment

It was intended that spill measurements would be performed by laboratory demonstrators on large groups of students during the lab. To avoid additional burden on the demonstrators, the technique had to be straightforward. To achieve this, each student had a sheet of paper (60 cm width, 49 cm depth) designed to protect surfaces from chemical spillage (Benchguard BG-50E extra-absorbent paper) placed in their half of the shared fumehoods and on which they carried out all their volumetric handling (weighing of solids for making up stock solutions was carried out elsewhere on communal balances).

The paper used has an absorbent side, and when solutions were spilled onto this in a controlled manner from a comparatively low height (a few centimeters, thought to be representative of many of the spills by the students), the initially localized spill soaked in and spread out over a few seconds to give a visible area of contamination (see Figure for examples). To confirm that all spillages of the copper compounds and dilutions would be visible, the stock solutions and the most dilute solution were spilled in a controlled manner onto the paper sheets using a micropipette. All were visible immediately after the spill, and after 1–2 h.

Figure 1

Examples of controlled volumes (left to right, 0.25–1.00 cm3) of 0.05 M copper acetate solution spilled onto lab paper, showing a well-defined edge.

To measure the area of visible stains produced by student spillage, a 2 × 2 cm2 grid on an A3 clear plastic sheet was overlaid, and for each student the number of squares in which any stain appeared was counted (by author A.H.). For 25 students, area measurements were also done using a 1 × 1 cm2 grid, with the results highly correlated and directly proportional, with the 1 × 1 cm2 grid values being ca. 10% lower than for the 2 × 2 cm2 grid. Therefore, to speed up evaluation, a 2 × 2 cm2 grid was used with a 10% adjustment.

To convert the area of spillage into volume spilled, a range of volumes of a 0.05 M solution of copper acetate were dropped onto the paper in a controlled manner using a micropipette, and the resultant areas of spill measured. The relationship between volume spilled and area measured was close to directly proportional, with a standard error of the gradient on the order of 5%. One limitation of this approach is that overlapping spills would only be counted once; hence, this may underestimate spillage.

The chemical spillage of two cohorts of year 1 undergraduate chemistry students has been examined. For the first cohort of students, the amount of spillage during this lab practical was measured for 64 out of 66 students, which was one-third of the cohort undertaking the concentration determination experiment during the week of this preliminary spills investigation. The total volume of chemical spilled during this practical was approximately 148 cm3, which was 1.2% of the total handled, ca. 1.3 × 104 cm3 (64 students handling ca. 200 cm3 of solution each throughout the day-long experiment). The amount spilled by individual students varied over a wide range, from ca. 0.02% to ca. 10% of the volume handled. The distribution of students’ spillages is shown in Figure , which highlights that for ca. 90% of the spillages over an amount approaching 2 orders of magnitude, this logarithmic graph is approximately linear; therefore, the distribution of volumes is approximately exponential for most spillages.

Figure 2

Volumes of solution spilled by 64 students as percentage of total handled and in cm3 (ordered left to right, lowest to highest).

Feedback Tool for Lab Demonstrators on Chemical Spillage by Students

When carried out by demonstrators during a lab practical, the technique using a 2 × 2 cm2 grid in the preliminary study for measuring spills was judged to be too time-consuming for larger spills. Therefore, it was slightly adapted to make it faster for demonstrators by having a larger 3 × 3 cm3 grid, with an insert of 1.5 × 1.5 cm3 for smaller spills. Observations of demonstrators using this larger grid indicate a typical time required for counting the spillage squares as ca. 15–20 s per student.

A simple tool (available in the Supporting Information) was developed to allow demonstrators (all Ph.D. students) to give prompt, in-lab formative feedback to students on the volume of chemicals they have spilled. This included set phrases on the potential consequences of the volume they spilled, with reference to a small number of well-known chemicals (ethanol, ethyl acetate, hexane, and 1 M potassium cyanide). For these chemicals the volumes corresponding to the derived no effect level (DNEL) for long-term dermal exposure were used,[19] along with a worst-case scenario assumption that all spilled chemical came in contact with the students’ skin. These chemicals were chosen to give nominal threshold safe spillage volumes covering the range of spillages noted in the preliminary study and were calculated assuming a 66 kg worker,[20] shown in Table (the DNELs quoted are the mass of chemical in milligrams of dermal exposure per kilogram of body weight per day, for a worker).

Table 1

Derived No Effect Levels, Nominal Safe Long-Term Exposure Limits, and Equivalent Number of 3 × 3 cm2 Squares for the Four Selected Threshold Chemicals

Chemical	DNELa for Dermal Exposure/mg/kg bw/Day	Nominal Safe Limit per Personb per Day/cm3	Number of 3 × 3 cm2 Squares Corresponding to Safe Volume
Ethanol	343	28.7	146
Ethyl acetate	63	4.6	27
Hexane	10.3	1.04	9
KCN 1M	0.14	0.14	2

For more on DNELs (derived no effect levels), see ref (19).

Assuming an average of a 66 kg person, see ref (20).

Utilizing the thresholds from Table , set phrases were developed for the demonstrators to give to the students on the basis of the amount of chemical spilled by students (Table ). The numbers of squares were slightly rounded to make it easier for demonstrators to rapidly provide feedback to students.

Table 2

Feedback Phrases Given by Demonstrators to Students Based on the Number of Squares Spilled for Each Student

Number of (3 × 3 cm2) Squares with Chemical Spilled	Feedback	Descriptive Grade
	“If you spilled this volume of chemicals routinely, then you would”:
<2	“be able to handle high hazard chemicals safely, such as 1 M potassium cyanide”	A
2–10	“be able to handle high hazard solvents, such as hexane, safely but not more hazardous chemicals, such as cyanides”	B
10–30	“be able to handle routinely hazardous chemicals safely, such as ethyl acetate, but not more hazardous chemicals, such as hexane or cyanides”	C
30–150	“be able to handle low hazard chemicals safely (such as ethanol), but not more hazardous chemicals”	D
>150	“not be able to handle even low hazard chemicals safely, such as ethanol”	E

This feedback was formative, and the students were informed that measuring spillage was not summatively assessed.[21] The demonstrators’ tool also had indicative descriptive grades (A–E) that they could give to the students, to provide a shorthand measure of how well they were handling the chemicals without spillage.

Randomized Controlled Trial of Effect of Feedback on Chemical Spillage

RCT Methodology

The effect of this demonstrators’ spillage feedback tool on the amount of chemicals subsequently spilled by students was investigated using a randomized controlled trial (RCT) with a second cohort of students. As the students undertook the experiment twice, once in the morning and once in the afternoon, they were split into intervention and control groups, with the former receiving feedback after the morning session on the amount of chemicals they spilled and possible consequences of this. The volume of chemical spilled during the afternoon session was measured, and a comparison of the amounts spilled was made for the control (no feedback) and intervention (received feedback) groups.

This was a parallel group randomized controlled trial, with 1:1 allocation to intervention:control. This was also a waiting list randomized controlled trial as feedback was given to all students, just not at the same time (nomenclature derived from its origin in medical RCTs): students allocated to the control group received feedback at the end of the afternoon experiment, to help minimize any potential ethical concerns related to different students receiving a different educational experience.[22,23] Eligibility criteria for participants was solely that they were first year undergraduate chemistry students who gave consent, at the University of York, U.K. The intervention group received feedback on their spillage for the morning experiment before carrying out the second experiment; the control group did not receive feedback prior to the afternoon experiment. The primary outcome of the RCT was the volume spilled during the afternoon experiments.

There have been no previous estimates upon which to base a sample size calculation; therefore, the sample size used was the year 1 Chemistry cohort, which was 185 students, consenting to take part in this RCT. No interim analyses or stopping criteria were put in place for this RCT.

It is good practice in the design of RCTs to take into account prognostic factors (factors that are known to affect an outcome) which may, by chance, not be equally distributed across groups. For instance, the randomization may be stratified to ensure that the control and intervention groups are similar in respect of people with these factors (e.g., age or gender). However, as there is no prior evidence on which factors can affect the amount of chemicals spilled by individuals, no stratified randomization of factors was attempted. Allocation of the students to the control and intervention groups was achieved by giving a random number between 0 and 1 to each student who had given consent using the Excel RAND function, then ordering the students by this random number, with the lowest 50% allocated to the control group, and the highest 50% to the intervention group. Using a computer for the randomization process decreases the possibility of bias affecting the outcome.[24]

To implement the allocation, a list was given to the demonstrators overseeing the morning experiment with the names of the students assigned into the control and intervention groups. The control/intervention allocation list was not revealed to any students. The random allocation sequence, enrollment of participants, and assignment of participants to the intervention and control group was carried out by an author (M.S.S.).

Assessment was blinded, as demonstrators overseeing the afternoon experiment were different from the morning demonstrators and they were not given the group allocation list (they were also requested to not ask the morning demonstrators or the students whether they had received feedback during the morning session). Therefore, the demonstrators assessing how much chemical the student spilled in the afternoon did not know who received feedback in the morning.

For the primary outcome, two nonparametric statistical tools were prespecified in the trial protocol (available in the Supporting Information). As the data obtained was non-normally distributed, nonparametric statistical tools were used to measure the difference in volume spilled, with the prespecified summary statistic for the effect size being the Hodges–Lehmann estimator and associated 95% confidence intervals, and the primary inferential statistic being the Mann–Whitney U test with a prespecified confidence level of 0.05. The former is a measure of the median difference between the intervention and control groups which returns the median of all possible differences between the control and intervention groups (here, 5092 = 67 × 76) and gives a more reliable measure for non-normal data than a simple comparison of the medians of the two groups.[25,26]This approach also allows for confidence intervals to be evaluated,[27] while the latter is a two-sided test of significance for independent observations used here to examine whether providing the feedback is statistically significant.[28] The prespecified null hypothesis investigated is that providing feedback has no effect on the volume of chemical subsequently spilled by the students. The Mann–Whitney U test is typically used for ordinal outputs, so it is used here with rankings of volume spilled by the students.

No other hypotheses were prespecified or tested during this trial to avoid the need to reduce the confidence level used to adjust for the problem of multiple comparisons.[29] There were no deviations or alternations between the statistical methods proposed to be used in the trial protocol and those implemented in the trial.

Results of RCT of Effect of Feedback on Chemical Spillage

Of the 185 students in the year 1 cohort, 150 consented to take part in this trial (81% of cohort), with 75 allocated to each of the control and intervention groups. Five students did not attend the practical, while five were provided an intervention contrary to that indicated by randomization (two received feedback when they were allocated to the control group, while three allocated to the intervention group did not receive feedback).

The consent form for student participation in the randomized trial was circulated from the 24th of September 2018 until the 12th of October 2018. The trial ran from the 22nd of October until the 9th of November 2018.

The average (mean) A-level tariff of the students was 177 (approximately 3 A’s at A-level), and the male/female ratio was 55/45;[30] the average age of students was 18–19 years old. This data is not available for the control and intervention groups.

There were 67 students who received the intervention, i.e., feedback on spillage, and 76 students did not receive the intervention. This is shown in the CONSORT (consolidated standards of reporting trials) flow diagram, Figure , which is a set of benchmark guidelines designed to allow for more straightforward replication and subsequent synthesis with future findings into a combined result using a meta-analysis of more than one study on a topic.[31]

Figure 3

CONSORT flow diagram for the transparent reporting of trials (consolidated standards of reporting trials).[31]

There were 5 absences from the lab, and data was not collected for 2 participants. As prespecified in the trial protocol, results for these individuals were excluded from the study.

All calculations were performed both in Excel and SPSS.[32] The statistical analysis was performed using a per protocol approach[33] (i.e., that analysis was performed on the basis of what the students actually received), and also an intention to treat analysis (i.e., that analysis is based on which group the student was allocated to).[34] However, following interview of the demonstrators for the five students who received a different treatment from that allocated by randomization, they indicated that this was not due to any conscious decision by them but due to oversight and was thought to be random; therefore, per protocol statistics are given as the primary choice of analysis.

The volumes of chemicals spilled by the control and intervention groups are shown in Figure and are also displayed in Figure with a logarithmic vertical axis. Also included on the secondary vertical axes is the approximate percentage of the volume handled that was spilled (which was ca. 100 cm3 per student for this afternoon session).

Figure 4

Volumes of solution spilled by 67 students receiving the feedback intervention and the 76 students not receiving this feedback (ordered left to right, lowest to highest).

Figure 5

Volumes of solution, displayed with logarithmic vertical axes, spilled by 67 students receiving the feedback intervention and the 76 students not receiving this feedback (ordered left to right, lowest to highest).

For the intervention group the median spillage postintervention was 0.071 cm3; the interquartile range (IQR) was 0.018–0.161 cm3 (range 0.00–4.99 cm3). For the control group the median spillage was 0.089 cm3, IQR 0.018–1.48 cm3 (range 0.00–13.8 cm3). The median is reported due to the skewed nature of the data.

The primary hypothesis testing statistical analysis performed was the Mann–Whitney U test, which gave a p value of 0.05, on the threshold of accepting or rejecting the null hypothesis given the prespecified 95% confidence limits stated in the trial protocol.[28] There is no assumption for normality of the data for this test.[35]

The effect size was estimated using the Hodges–Lehmann estimator, which is a measure of the median difference between all the different possible pairing between control and intervention groups (67 × 76 = 5092 pairings). It does not assume normal distribution for the control and intervention data sets but does assume an asymptotic approach to normal distribution of the differences.[36]

Two approaches were used in determining the Hodges–Lehmann estimator; in one the analysis was performed using absolute differences of volume spilled between control and intervention groups, while in the second, the analysis was performed using differences of the log10(volume). Both volume and log volume analyses are presented where there is a noticeable difference between the two. It is worth noting that the analysis performed using differences of the log10(volume) spilled is equivalent to the ratio of the amount spilled by the control group over the intervention group, so it is easily expressible as a percentage change in amount spilled by giving the feedback intervention.

Furthermore, the log volume data distribution of the differences gives a symmetrical bell-shaped distribution, while the volume data does not, so since near normality of the distribution of the differences is an assumption of the Hodges–Lehmann method, analysis by log volume is cited with preference here.[25,37] This is described in more detail in the Supporting Information.

Demonstrators recorded that a small number of students spilled no chemical. By contrast, in the preliminary investigation the volume spilled was measured by an author (A.H.) after the experiment was completed so was not under the time pressure the demonstrators were under and recorded no zero spillages. Hence, it is possible that spillage measurements carried out by demonstrators may have missed very small, dilute, spillages. It is estimated that, in practice, a minimum spill amount observable by the demonstrators given their limited time would be ca. 0.001 cm3, and that value was used instead of 0 to allow a logarithm for this analysis to be obtained. To permit a sensitivity analysis on this lower limit, calculations were redone assuming a minimum value spilled a factor of 10 higher at 0.01 cm3, and it was found that the Hodges–Lehmann estimator and the confidence intervals were unaffected.

The Hodges–Lehmann estimator for the median difference between intervention and control logged volumes is −0.301, which is equivalent to those receiving the intervention spilling approximately half the volume spilled by the control students, a 50% decrease in chemical spillage due to receiving feedback. The 95% confidence interval for the Hodges–Lehmann estimator of the median difference for the logged data was 0 to −0.699, which is equivalent to those receiving the intervention spilling between the same volume spilled by the control students and 0.2 of that spilled by the control students, which alternatively represents a decrease in chemical spillage due to receiving feedback of between zero and a factor of 5.

A sensitivity analysis was also performed using both per protocol analysis and the intention to treat (ITT) method. In ITT analysis, students that were initially allocated to the intervention group but did not receive feedback were still included in the intervention group and vice versa. The ITT Hodges–Lehmann median was −0.301, with an upper limit of 0 and lower limit of −0.602 similar to the per protocol analysis (−0.301, 0, and −0.699, respectively). The p value for the Mann–Whitney test was somewhat different at 0.09 using the ITT approach. There were no important harms or unintended effects noted in either group for this trial.

Discussion

This randomized control trial measured the effect of providing feedback about spillage to undergraduate chemistry students on the amount of chemical subsequently spilled. The result showed a (Hodges–Lehmann) median decrease of 50% in chemical spillage by students receiving feedback. The Mann–Whitney test result is on the threshold of classifying this change as statistically significant, given the measured p value of 0.05 determined and a 95% confidence limit prespecified in the trial protocol, and there has been some discussion in the literature on the relative merit of quoting p values or effect sizes and corresponding confidence intervals, particularly when close to confidence limits for rejecting the null hypothesis; both are quoted here.[38−41]

Potential limitations of this RCT study include that the calculation of the Hodges–Lehmann estimator in terms of volume or log volume was not prespecified in the trial protocol. As the distribution of differences is not close to normally distributed, while the logged data is near to a normal distribution and the latter gives a relative effect size straightforwardly, analysis using logged volumes is given preference here.

Another potential limitation is that the randomization of students and the analysis of the data were done by the authors of this paper and not by an independent third party.[42] This is due to the fact that only two people were conducting the trial. An attempt to mitigate this issue was through having a prespecified protocol, and primary analysis and randomization carried out by different authors (A.M.T. and M.S.S., respectively).

Despite randomized control trials being able to reduce or eliminate selection bias,[24] some sources of bias might be present, for instance, baseline differences between control and intervention groups.[42] However, these differences were not available for the control and intervention groups, and also there is insufficient knowledge of which factors, if any, may affect chemical handling skills. There is also a possibility that members of the control group could have discussed the feedback with a member of the intervention group before the afternoon experiments, or overheard this feedback being given to someone else. This potential contamination bias could have the effect of causing the observed effect size to be underestimated, but this is difficult to avoid or quantify in the typical lab setting. A per protocol analysis has been adopted in this trial as the preferred method to report; however, it has been observed that per protocol and intention to treat analysis can give different results to an extent, and so results using both methods are reported here.[43]

These potential limitations notwithstanding, this trial was designed to be a pragmatic RCT and so seeks to be representative of possible implementation elsewhere.[44] Nothing significant was altered in the procedure for the practical for this feedback on spillage to be given. The chemicals spilled were measured by demonstrators who were already assigned to oversee this practical. This approach could be applicable to other institutions’ laboratories carrying out undergraduate volumetric analysis experiments, and it fulfills 11 out of 12 eligibility criteria for pragmatic trials (excepting intention to treat analysis).[45]

This randomized control trial is also original for the field as no other RCTs have been conducted on teaching techniques aimed at reducing the amount of chemicals the students spill. A literature review indicates limited RCTs in the field of education research,[46] including in chemistry education research on classroom-based teaching (for example, on the effect of peer-led team learning[47]) and none in the field of teaching methods to improve laboratory practical skills. The closest parallels to this study are in RCTs on other motor skills, for instance, in assessment of different approaches to teaching surgery skills,[48] assessment of different approaches to motor skill development in preschool children,[49] or school-based driver education for preventing accidents.[50]

A survey was carried out of those with U.K. university chemical safety roles to ask what percentage reduction in spillage they would consider sufficiently meaningful to make it worthwhile to adapt their lab practicals. Although there was only a low response rate of six respondents, the mean worthwhile reduction reported was 40%, so the reduction in chemical spillage of 50% found in this trial may be judged of sufficient size to be worthwhile for implementation of this technique.

The RCT result does bear some uncertainty, as the confidence intervals range from 0 to 80%. However, as there were no harms in this trial and only minimal expense was needed (except from minimum amount required to acquire the paper, ca. 1 $/£/€ and ca. 1 min per student), the benefits may be judged to likely outweigh the uncertainty for this trial and could make it applicable to other educational institutions for replication or possibly implementation as part of the undergraduate curricula.

Conclusions

A technique is reported for measuring the volume of chemical spilled during undergraduate laboratory practical classes and has been used to evaluate for the first time the distribution of spillage among a class of 64 students, showing a very wide range in volumes spilled, ca. 3 orders of magnitude. This measuring technique has been adapted into a reliable tool for laboratory demonstrators, allowing them to rapidly measure spillage during practical classes and provide individual feedback to students on possible consequences of this and future spillages.

A randomized controlled trial has been carried out on 150 consenting year 1 undergraduate chemistry students, to evaluate the effects of providing feedback to students on the volume of chemical they spilled by measuring its impact on subsequent spillage of chemical. The (Hodges–Lehmann estimator for the) median change in volume spilled due to providing feedback was a 50% lower volume spilled (95% confidence range: 0 to 80% decrease, Mann–Whitney U test, p = 0.05).

As this spills feedback was implemented in a pragmatic manner, using lab demonstrators and volumetric experiments that the students routinely carry out, and as the relative cost per student of providing feedback on spillage is comparatively low (ca. 1 $/£/€ and ca. 1 min per student), and the median reduction in spillage was potentially significant, there is merit in this spills measurement and feedback being evaluated in other institutions, either as an educational tool, or using the waiting list RCT structure described here to provide improved confidence limits on the size of the effect measured here.

This study highlights that although there have been well-discussed issues with carrying out RCTs in the chemistry education field,[51] the use of the waiting list RCT design offers a methodology to investigate the effects of educational techniques that is perceived as fairer for the participants while having the benefits of randomization for reducing bias.[52]

Another issue highlighted in chemical education research is in achieving a sufficient number of subjects for a statistically useful result to be achieved.[51] This study demonstrates that, where an educational approach is delivered to the individual, a cohort in a typical degree course at a single university can provide sufficient subjects to allow the detection of effect sizes of a meaningful magnitude, helped here by having a strong sign-up rate when seeking consent of ca. 80%, possibly benefited by using the waiting list trial design. Therefore, this format of RCT could help to address some of the issues of replication of findings, discussed recently in the chemistry education sector,[53] following well-documented concerns raised about the reproducibility of reported findings in other fields with human subjects.[54]

To assist with any potential future studies on this topic, the results from this RCT are presented, as far as possible, using the CONSORT guidelines for reporting RCTs.[31]