The short- and long-term impact of an incentive intervention on healthier eating: A quasi-experiment in primary- and secondary-school cafeterias in Brazil

Abstract

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.Participants Students 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.