Author's response to reviews Title: Healthy snacks at the checkout counter: A lab and field study on the impact of shelf arrangement and assortment structure on consumer choices Authors: Ellen van Kleef (Ellen.vanKleef@wur.nl) Kai Otten (kai_otten@hotmail.com) Hans C.M. van Trijp (Hans.vanTrijp@wur.nl) Version: 4 Date: 5 November 2012 Author's response to reviews: see over
November 5, 2012 Dear Dr Silvano Gallus, Attached you find the revised paper Healthy snacks at the checkout counter: a lab and field study on the impact of shelf arrangement and assortment structure on consumer choices (manuscript ID 7456086776880802). The authors would like to thank the reviewers for their valuable comments and suggestions. To facilitate the evaluation of our revised paper, we have addressed each of the reviewers comments, and provided details of these changes in a later attached document. We have attempted to address all of the comments in the revised manuscript. Again, we believe that the paper has improved thanks to the useful suggestions. We look forward to hearing your conclusion on the paper. Yours sincerely, also on behalf of the co-authors Kai Otten and Hans van Trijp. Ellen van Kleef (Ellen.vanKleef@wur.nl) 1
Revision note paper Healthy snacks at the checkout counter: A lab and field study on the impact of shelf arrangement and assortment structure on consumer choices Reviewer's report: Reviewer: Marijn Stok The manuscript describes two studies (one lab study and one field study) investigating the results of manipulations of availability and accessibility of healthy and unhealthy snacks at the checkout counter. The study addresses a timely and important topic and does so in a sound and well-thought out manner. The potential interactive effects between availability and accessibility are an interesting issue, which has not received much attention to date. Nevertheless, there are also some issues with the manuscript that should be addressed. - Major Compulsory Revisions 1. The Abstract should reflect not only the obtained significant findings for availability, but also the non-significant findings for accessibility and for the interaction between both factors. We now also included non-significant findings in the abstract. This part of the abstract now reads as follows (page 2, results section of abstract): Regarding shelf display location of healthy snacks, no significant differences were observed. There was also no significant shelf arrangement by assortment structure interactive effect. The field study replicated these findings, in that this assortment structure led to higher sales of healthy snacks. Sales of unhealthy and total snacks were not impacted by manipulations (no main or interaction effects). 2. The hypotheses posed in the Introduction (last paragraph) discuss only the combined effect of availability and accessibility, while the results section pay most attention to main effects of these factors. This should be reflected in the hypotheses. We rewrote the hypothesis as follows (page 7, introduction, last paragraph): For both studies, it was hypothesized that the individual and combined effect of increasing the availability of healthy snacks (while at the same time not banning unhealthy snacks) and positioning them at the top of the shelf display would increase sales of these healthy options. 3. Methods, procedure and materials, first paragraph: Participants are asked to select their favourite snack. Why was the question posed like this? Isn t this something else than the snack they would be most likely to choose in the situation they had to imagine? A discussion of whether this may be of influence on the results is in order. Indeed, how a question is asked may substantially influence the answers being given. We choose for this wording of favourite snack as we assumed that given the instruction of having to imagine being at the university canteen around 4 o clock in the afternoon and selecting a favourite snack would correspond most to what typically happens in real life. Nevertheless, selecting a favourite snack instead of selecting a snack may put emphasis 2
on taste and liking more than what a study may typically purchase. Therefore, in the conclusions section we now added (page 17): Perhaps the assortment did not look like a typical snack assortment at a university canteen or the instruction being given (select favourite snack) influenced choice. 4. The Methods, measures section introduces a number of variables that are not previously discussed. Why are satisfaction, realism and mood assessed, what is their relevance? This should be included in the introduction. Moreover, it does not become clear (also not from the order of reporting in the results section) if these variables are seen as separate dependent variables of interest or if they serve as manipulation check variables to make sure that the manipulation did not influence these factors. Choice satisfaction was assessed as a separate dependent variable of interest as the idea behind nudging is that consumers are equally satisfied with their choice and do not feel pressurized to make a different choice. We now include this choice satisfaction variable in the introduction in the section about ethical concerns (page 7): Therefore, an additional aim of this study is that we also examined participants perception of their freedom in making choices and choice satisfaction. We included assortment realism and mood as a manipulation checks to examine whether these factors influenced our manipulation. We added that to the measures section (page 9): To rule out reasons why the manipulations may (not) influence choice, assortment realism and mood were measured as manipulation checks. 5. Method, field study, design, paragraph 2: could lower price of the fruits influence choice? Should this be discussed? Were the items exactly identical to those in the lab study? Were the amounts the same (12 vs 4, so 16 in total)? How were the participants choices recorded? Did participants realize their choices were recorded? Some more information about the setup should be provided to clear up these questions. In the conclusions section, we now refer to the lower price of the fruits as a limitation of the study. It reads as follows (page 17): In the field study, fruit had a lower price which may have given these products an additional benefit. Although the total number of items was similar to the lab study, the items themselves were not exactly the same as in the lab study. We now describe this more clearly in the methodology section (page 11): Although the same nutrition criteria to select healthy and unhealthy snacks were applied, due to availability not all type of snacks were similar to the snacks used in the lab study. The number of available snacks was the same: 16 in total (12 versus 4 depending on conditions). We now describe more extensively how data was collected during the field study (page 12): During the four experimental weeks, sales data were collected by staff canteen employees on a daily basis by counting the number of snacks left at the end of each day. It was not communicated to visitors that a study was going on. 3
6. Results, Study 1, paragraph 2: the assortments with 75% unhealthy snacks were considered by the participants as more realistic. Does this mean anything for the interpretability of the results? Could it not be the case that students, seeing the unrealistically high number on unhealthy snacks, responded to perceived demand characteristics to choose a healthy snack? This should be addressed in the discussion section. We agree that this finding may be related to a demand effect when participants had to make a choice during the study. We therefore now describe this in the conclusions section (page 17): Additionally, the assortments with 75% unhealthy snacks were seen as more realistic than assortments with 25% unhealthy snacks. The increased healthy choices may be due to the demand effects of the research context which may have hinted at health and food choices. 7. Results from Study 2 show that the assortments with 75% healthy snacks resulted in higher purchase of healthy snacks. The amount of unhealthy snacks did not decrease, however: in all, participants thus seem to consume more in total. If that would indeed be the case, would it then still be a good (good in terms of implications for public health) result that healthy item purchase increases so much? It would only lead to higher consumption in total, and thus a higher amount of kcal! On the other hand however, you do report that total consumption does not differ between conditions. How can that be when healthy snacks increase and unhealthy snacks remain the same? The total of that would be an increase, I would think. When I look at Figure 3, there do seem to be differences also in unhealthy snacks and total snacks. More discussion of these results is in order. We see the same trends in the field study data as the reviewer notices. Indeed, consumption of unhealthy snacks is not significantly different among conditions, but figure 4 (figure 3 in initial paper) shows that when 75% of the assortment consists out of healthy snacks, people seem more seduced to purchase a snack. Also, putting healthy snacks at lower shelves seems to make people less inclined to purchase them. Repeated measures ANOVA also shows trends towards these directions. For example, the main effect of assortment structure on sales of unhealthy snacks is marginally significant at p=0.09. However, in accordance with common practice, we decided to only consider a p-level smaller than 0.05 as statistically significant. Moreover, we corrected the analysis for number of visitors per day. Data was limited, as we now also indicate in the conclusions section (page 16). In terms of implications for public health, our perspective is that snacking is not necessarily unhealthy. Within a snack choice moment, our viewpoint is that it would be beneficial if consumers would choose low caloric or fruit snacks instead of regular, more energy dense snacks. 4
- Minor Essential Revisions 1. Degrees of freedom for ANOVA and Chi Square test results are missing. We now report degrees of freedom for ANOVA and Chi Square test results. 2. Standard deviations are missing. We now report all standard deviations 3. There are some wording and phrasing issues that should be addressed (e.g. introduction, first paragraph: how can a daily frequency increase? Does this mean that on more days, one snack is taken, or that on any given day, more snacks are taken, or something else still; introduction, second paragraph: interventions are without ban on forbidden products; introduction, fourth paragraph: No research to date combined both effects to better understand their potential; results, field study, survey, paragraph 2: that should be removed in the first sentence; etc.) We made the suggested textual changes and rewrote the sentence about snacking to clarify the research findings (page 4): Over the past decades, the number of snacking occasions per day and energy density of snacks have increased substantially [5]. 4. Method, field study, survey, paragraph 1. Did the researchers check (via a question) whether participants had indeed visited the canteen in the previous weeks? No, it has not been checked whether the participants visited the canteen in the previous weeks. - Discretionary Revisions - Minor issues not for publication 1. consistency in data reporting (P vs P vs p; F = 0.19 vs F < 1). We now consistently use a small p and always report the F-value. 2. consistency across figure 2 and 3 (same order on X-axis in both would be easier to follow) We changed of the conditions displayed in the chart. 3. consistency in headings: in the results section, the headings are Study 1 vs Field study. This should be either Study 1/Study 2 or Lab study / Field study. Study 1 is now consistently called lab study and study 2 field study. Reviewer's report Reviewer: Emely De Vet In this manuscript the authors present two experimental studies testing two different nudges simultaneously. Addressing the food environment in a subtle way, such as with the proposed nudges, is a promising and innovative strategy in promoting healthier food choices. The literature on effective nudges is still scarce, and the present manuscript provides a valuable contribution to it. I specifically appreciate the approach the authors have chosen to start with a 5
highly controlled experimental test in a laboratory setting, followed by a replication in a more ecologically valid setting, a worksite cafeteria in a hospital. Although I am very positive about this kind of work, I also noticed some issues in the manuscript that I would like to see addressed. Major compulsory revisions 1. The authors adequately address what previous studies on accessibility and availability have found, but I miss a more in-depth or theoretical analyses of why and how these nudges might work. We thank the reviewer for pointing at this lack of theoretical analysis of how nudges might work. We now elaborate on potential reasons why increased accessibility and availability of health snacks may work (introduction, page 6): The interventions in our study aim to take advantage of biases related to easy accessibility and availability. Altering the ease of access to snacks basically means that it requires less effort to obtain them. People furthermore have the tendency to go for the default option as this typically requires the least effort due to habits or even laziness [22]. Availability can influence consumer choices in various ways. More snacks healthy snacks present for purchase increases the likelihood that consumers find a snack that fits their need. Higher availability of healthy snacks leads to a larger assortment which tend to raise consumer expectations and satisfy consumers with a high need for variety [19, 23]. By enlarging the available assortment of healthy snacks, we made these snacks the implicit default. This may function as a cue that implies a consumption norm. 2. The authors simultaneously address accessibility and availability, but do not define the concepts of accessibility and availability differ, and it may thus not be clear to all readers why these are different concepts. We now explain how accessibility and availability are defined in our study (introduction, page 5 and 6): In this study, accessibility is defined as the convenience or closeness of physically obtaining a product in a shelf space. We define availability as the presence of snacks ready for immediate choice by consumers. Before discussing the studies in this field, we now start by stating that availability and accessibility have been conceptualized in various ways in food studies (introduction, page 4): In food studies, availability and accessibility has been conceptualized in various ways, such as spatial accessibility and means of transportation to stores [12]. 3. It is not clear what the exact hypotheses of the studies are. The authors make a statement about the combined effect of the two nudges, but the justification for this hypothesis seems to be missing. Also it is not clear what the authors expect from the individual nudges. In accordance with reviewer 1, we now added the combined effect of the availability and accessibility manipulation to our hypothesis. To clarify the justification of our hypothesis, we now summarize the theoretical reasons why these nudges may work in the following way (page 7): To summarize, changes in a snack assortment in terms of effort required to actually grab a product and the size of an assortment may make healthier snacks more salient, attractive, normative and convenient. For both studies, it 6
was hypothesized that the individual and combined effect of increasing the availability of healthy snacks (while at the same time not banning unhealthy snacks) and positioning them at the top of the shelf display would increase sales of these healthy options. 4. How were the food products selected? Were they pre-tested? It would be relevant to know participants ratings of healthiness and attractiveness of the products in study 1 as well. The selection of products was primarily based on the guidelines of the Netherlands Nutrition Centre. Besides that, we choose a selection of familiar snacks (e.g. snacks that are available in Dutch supermarkets, such as Mars chocolate brands). We did not pre-tested the individual foods on their perceived healthiness and attractiveness. 5. Data analysis of study 1: It is not clear why feelings of hunger were entered as a covariate. Did feelings of hunger correlate with either condition or with the dependent variable? If so, it would be good to report these correlations. If not, then hunger is not strictly needed as a control variable, and the unadjusted model could be reported. Also, I would be interested in the role of other potential covariates such as age and gender. Were these related to condition or food choice? We now checked whether randomization of respondents across conditions was successful in terms of feelings of hunger, gender and age. We now report these analyses in the results section as follows (page 10, results lab study): There were no differences in gender (χ 2 (1, N=158)=0.03, p=.87) or feelings of hunger (all Fs<1.70, all ps>0.19) across the four conditions. However, there was a trend towards an age difference across conditions (interaction between assortment structure and shelf arrangement and F(1,154)=3.71, p=.06) and therefore in the logistic regression analysis we included age as covariate to control for influence. Feelings of hunger were not different across conditions so we agree with the reviewer that this variable is hence not needed as a control variable. 6. Design of study 2: The price of fresh fruits is considerably lower than the price of other food products. This would suggest that the availability manipulation is also an accessibility manipulation, in that sense that increasing the proportion of healthy products in the assortment also increases the number of cheap, and thus more accessible, products. How may price differences have influenced the results? In the conclusions section (page 17), we now refer to the lower price of the fruits as a limitation of the study. It reads as follows: In the field study, fruit had a lower price which may have given these products an additional benefit. Minor essential revisions 1. Study 1, procedure and materials: pictures or screen shots would help to understand the on-screen choice environment. We now added a figure with a screenshot of one of the virtual shelves (new figure 1). 7
2. Please report the odds ratios and confidence intervals of the ORs in study 1 We now report the odd ratio of the significant main effect of assortment structure including its confidence interval (page 10). Discretionary revisions 1. Data- analysis study 2: I think the interaction term was also added in the repeated measures analyses, but is not reported here. We now report all interaction terms (page 15). 2. I found it quite hard to follow that the paper first describes the methods of both studies, followed by the results of both studies. I would find it more readable if the methods and results of study 1 are described first, followed by the methods and results of study 2. We changed the sequence of studies in the way the reviewer suggests. Editors remarks Also, please make the following formatting changes during revision of your manuscript. Ensuring that the manuscript meets the journal?s manuscript structure will help to speed the production process if your manuscript is accepted for publication. 1. Please change the title 'Introduction' to 'Background'. We made this change. 2. Figure titles: All figures must have a figure title listed after the references in the manuscript file. The figure file should not include the title or number (e.g. Figure 1... etc.). The figures are numbered automatically in the order in which they are uploaded. For more information, see the instructions for authors: http://www.biomedcentral.com/info/ifora/figures. We made this change. 3. Figure cropping: It is important for the final layout of the manuscript that the figures are cropped as closely as possible to minimise white space around the image. For more information, see the instructions for authors: http://www.biomedcentral.com/info/ifora/figures. 8