Two observational studies examining the effect of a social norm and a health message on the purchase of vegetables in student canteen settings

Research output: Contribution to journalArticle

Authors

  • Eric Robinson
  • Paul Aveyard
  • Susan A Jebb
  • Peter Herman

External organisations

  • School of Psychology, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; Now at School of Management, University of Bath, Claverton Down, Bath, BA2 7AY, UK. Electronic address: e.i.m.collins@bath.ac.uk.
  • School of Psychology, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; Now at the Department of Psychology, Aston University, Birmingham, B4 7ET, UK. Electronic address: thomasjm@bham.ac.uk.
  • University of Liverpool
  • Nuffield Department of Primary Care Health Sciences, Radcliffe Observatory Quarter, University of Oxford, Oxford, OX2 6GG, UK. Electronic address: paul.aveyard@phc.ox.ac.uk.
  • Nuffield Department of Primary Care Health Sciences, Radcliffe Observatory Quarter, University of Oxford, Oxford, OX2 6GG, UK. Electronic address: susan.jebb@phc.ox.ac.uk.
  • Department of Psychology, University of Toronto, Toronto, Ontario, Canada, M5S 3G3. Electronic address: herman@psych.utoronto.ca.

Abstract

There is some evidence from laboratory-based studies that descriptive social-norm messages are associated with increased consumption of vegetables, but evidence of their effectiveness in real-world settings is limited. In two observational field studies taking an ecological approach, a vegetable-related social norm (e.g. "Did you know that most students here choose to eat vegetables with their meal?"), and a health message (e.g. "Did you know that students who choose to eat vegetables have a lower risk of heart disease?") were displayed in two different student canteens. Purchases were observed during three stages: baseline, intervention (when the posters were displayed) and immediate post-intervention (when the posters had been removed). Study 1 (n = 7598) observed the purchase of meals containing a portion of vegetables and Study 2 (n = 4052) observed the purchase of side portions of vegetables. In Study 1, relative to baseline, the social-norms intervention was associated with an increase in purchases of vegetables (from 63% to 68% of meals; OR = 1.24, CI = 1.03-1.49), which was sustained post-intervention (67% of meals; OR = 0.96, CI = 0.80-1.15). There was no effect of the health message (75% of meals at baseline, and 74% during the intervention; OR = 0.98, CI = 0.83-1.15). In Study 2, relative to baseline, there was an effect of both the social norm (22.9% of meals at baseline, rising to 32.5% during the intervention; OR = 1.62, CI = 1.27-2.05) and health message (rising from 43.8% at baseline to 52.8%; OR = 0.59, CI = 0.46-0.75). The increase was not sustained post-intervention for the social norm intervention (22.1%; OR = 0.59, CI = 0.46-0.75), but was sustained for the health intervention (48.1%; OR = 0.83, CI = 0.67-1.02). These results support further testing of the effectiveness of such messages in encouraging healthier eating and indicate the need for larger-scale testing at multiple sites using a randomised-controlled design.

Bibliographic note

Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Details

Original languageEnglish
Pages (from-to)122-130
Number of pages9
JournalAppetite
Volume132
Early online date1 Oct 2018
Publication statusPublished - 1 Jan 2019

Keywords

  • Social norms, Descriptive norm, Healthy eating, Vegetables, Field study