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.

BACKGROUND

Supermarkets 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.

OBJECTIVE

We 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.

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. In addition, individual and purchase characteristics were assessed by means of short surveys.

RESULTS

In 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).

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.