Two observational studies examining the effect of a social norm and a health message on the purchase of vegetables in student canteen settings
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- 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: firstname.lastname@example.org.
- 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: email@example.com.
- University of Liverpool
- Nuffield Department of Primary Care Health Sciences, Radcliffe Observatory Quarter, University of Oxford, Oxford, OX2 6GG, UK. Electronic address: firstname.lastname@example.org.
- Nuffield Department of Primary Care Health Sciences, Radcliffe Observatory Quarter, University of Oxford, Oxford, OX2 6GG, UK. Electronic address: email@example.com.
- Department of Psychology, University of Toronto, Toronto, Ontario, Canada, M5S 3G3. Electronic address: firstname.lastname@example.org.
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.
|Number of pages||9|
|Early online date||1 Oct 2018|
|Publication status||Published - 1 Jan 2019|
- Social norms, Descriptive norm, Healthy eating, Vegetables, Field study