Objective: To assess the short- and long-term effectiveness of a lottery incentive intervention to promote the purchase of healthy products in school cafeterias.
Design: A quasi-experiment in which students' purchases in intervention schools were analysed in a pre-post analysis and also compared with a control school in a difference-in-differences model. A hierarchical linear model assessed the mean number of promoted healthy products purchased daily per participant before (twenty-six weekdays), during (nine weekdays) and after (twenty-eight weekdays) the intervention period. Sex, age and prior purchasing behaviour served as covariates.
Setting: Convenience sample of school cafeterias using a debit-card payment method that allowed for the assessment of students' purchasing behaviour.ParticipantsStudents who used the pre-paid card to buy snacks at the school cafeteria. A total of 352 students (208 in intervention schools and 144 in control school) were included in the final analyses.
Results: The incentives programme significantly increased the purchase of promoted healthy products during (v. before) the intervention period in intervention schools (P<0·001), especially among younger children (P=0·036). Among the students who purchased the promoted healthier products during the intervention, there was an increase in total number of purchased products (healthy non-promoted, but also of less healthy products). Sex and past consumption behaviour did not influence the response to incentives in the short term. On average, no long-term effect was observed.
Conclusions: Long-term and negative spillover effects must be taken into consideration for a complete understanding of the effects of incentives on healthier eating.
Keywords: Eating habits; Healthy eating; Incentives; Quasi-experimental design; Schoolchildren.