Social norm nudges in shopping trolleys to promote vegetable purchases: A quasi-experimental study in a supermarket in a deprived urban area in the Netherlands

Marlijn Huitink,Maartje P Poelman,Emma Van Den Eynde,Jacob C Seidell,S Coosje Dijkstra

doi:10.1016/j.appet.2020.104655

Marlijn Huitink, Maartje P Poelman + Show 3 more

Open Access

https://doi.org/10.1016/j.appet.2020.104655

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Abstract

BackgroundSupermarkets are a key point of purchase for groceries and can therefore have a considerable influence on eating behaviours. Evidence suggests that descriptive social norm nudges in shopping trolleys can be effective in stimulating vegetable purchases in supermarkets. ObjectiveWe investigated the effect of a combination of two nudging strategies in shopping trolleys – a social norm about vegetable purchases and a designated place to put vegetables – on the amount of vegetables purchased in a supermarket in a deprived urban area in the Netherlands. DesignA quasi-experimental study was conducted with two conditions: 1) intervention days on which the shopping trolleys in the supermarket had a green nudge inlay indicating a place for vegetables and a social norm message and 2) control days on which the regular shopping trolleys (no inlay or social norm) were used in the supermarket. During both the intervention and control days, vegetable purchases were measured by means of the cash receipts collected from customers at the checkouts. In addition, individual and purchase characteristics were assessed by means of short surveys. ResultsIn total, 244 customers participated in the study. Ordinal logistic regression analyses showed that customers on the intervention days (n = 123) were in a higher tertile for grams of vegetables purchased compared to the customers on the control days (OR: 1.66, 95% CI: 1.03–2.69, p = 0.03), especially those who bought groceries for less than three days (OR: 3.24, 95% CI: 1.43–7.35, p = 0.003). Sensitivity analyses also showed that intervention customers who noticed the green inlay were even more likely to purchase more vegetables (OR: 1.86, 95% CI: 1.06–3.25, p = 0.02). ConclusionsThis quasi-experimental study showed that a nudge inlay in shopping trolleys communicating a social norm on vegetable purchases and indicating a distinct place to put vegetables in the trolley increased vegetable purchases among supermarket customers.

Highlights

Inadequate vegetable consumption is of considerable public health concern
To the best of our knowledge, these previous studies were conducted in supermarkets in neighbourhoods with a middle or high socioeconomic position (SEP), whereas it seems especially important to promote vegetable purchases among people from low-SEP groups, since they have a lower vegetable intake compared to people from higher SEP groups (Gallo et al, 2012; Giskes, Turrell, Van Lenthe, Brug, & Mackenbach, 2006). These previous studies used the amount of money spent on fruit and vegetables as an outcome measure, so it is not clear whether the customers purchased a larger amount of fruit and vegetables or whether they purchased fruit and vegetables that were more expensive. The aim of this quasi-experimental study was to investigate the effect of a combination of two single nudges in shopping trolleys – a social norm message about vegetable purchases and a designated place to put vegetables – on the amount of vegetables purchased in a supermarket in a deprived urban area in the Netherlands
We considered the number of grams of vegetables purchased and the number of items of vegetables purchased as dependent variables, while the condition was the independent variable

Summary

Introduction

Inadequate vegetable consumption is of considerable public health concern. A diet low in vegetables is associated with an increased risk of overweight and obesity, as well as chronic diseases such as type 2 diabetes, cardiovascular disease and certain types of cancers (Boeing et al, 2012; Key, 2011; Sotos-Prieto et al, 2017). Design: A quasi-experimental study was conducted with two conditions: 1) intervention days on which the shopping trolleys in the supermarket had a green nudge inlay indicating a place for vegetables and a social norm message and 2) control days on which the regular shopping trolleys (no inlay or social norm) were used in the supermarket. During both the intervention and control days, vegetable purchases were measured by means of the cash receipts collected from customers at the checkouts. Conclusions: This quasi-experimental study showed that a nudge inlay in shopping trolleys communicating a social norm on vegetable purchases and indicating a distinct place to put vegetables in the trolley increased vegetable purchases among supermarket customers

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