Plain English Summary
Background and study aims
Increasing the relative availability of healthier and more plant-based foods increases the likelihood that they are selected. The mechanisms by which this intervention has its effect are little explored. The aim of the two studies described here is to provide the first exploration of the role of perceived popularity – as a marker of descriptive social norms – as a possible mechanism underlying the effects of availability interventions.
Who can participate?
Adults over the age of 18
What does the study involve?
This study has two components that will be conducted at the same time, an online study and a lab study. Participants will be able to take part in one or the other.
Online Study: The study will be conducted online. Participants are shown eight images, each with a mix of healthier and less-healthy food or drink options on cafeteria shelves, and asked to indicate the percentage of sales they think would be of the healthier (over the less-healthy) options. These images will show either 75% healthier, 50% healthier, or 25% healthier options. The shelves in the images will either be full (i.e. have same number of units of products in each row), or emptier (i.e. have a varied number of units of products in each row, with maximum number of units equal to that in fuller shelf condition). Participants will be randomised to see one of these six options (3 availability x 2 shelf fullness). The data from the study will be used to assess whether altering the relative availability of healthier food alters the perceived popularity of these healthier foods.
Lab Study: Participants will be invited to take part in another study. After completion of this main study, and prior to debriefing, participants will be presented with a tray of food options and asked to select a snack, ostensibly as a thank you for their participation. Participants will be randomised to a particular arrangement of snacks on the tray. Trays will have either a 1:2 healthier:less-healthy snack ratio or 2:1 healthier:less-healthy snack ratio. Trays will also either be set out so that the tray appears full - suggesting greater consumption by others for options which have more units remaining – or so the tray appears emptier - suggesting greater consumption by others for options which have fewer units remaining. Participants’ selection of a healthier (over less-healthy) snack will be recorded. This study will assess the impact of manipulating perceptions of the popularity of healthier (over less-healthy) options on food selection.
What are the possible benefits and risks of participating?
Participants in the online study will be paid standard market research panel rates for participating in this study, and in the lab study will be paid for the main study they have been recruited to. There are no known risks of participating in either study.
Where is the study run from?
Behaviour and Health Research Unit, University of Cambridge (UK)
When is the study starting and how long is it expected to run for?
February 2020 to August 2020
Who is funding the study?
Wellcome Trust (UK)
Who is the main contact?
Dr Rachel Pechey
Increasing the relative availability of healthier vs. less-healthy food: Exploring the role of social norms
1. Increased availability of healthier (less-healthy) foods increases the perceived popularity of healthier (less-healthy) foods – when shelves are full
2. When shelves are emptier, decreased availability of healthier (less-healthy) foods decreases the perceived popularity of healthier (less-healthy) foods
3. Increased perceived popularity of healthier (less-healthy) foods increases selection of healthier (less-healthy) foods
4. Manipulating availability at the product-level will have a smaller impact than manipulating availability at the category-level
Increased availability of healthier (less-healthy) foods increases selection of healthier (less-healthy) foods when in line with perceived popularity (i.e. when offered a full tray), but this impact is countered when perceived popularity acts against increased availability (i.e. when tray is emptier)
Approved 14/01/2020, Cambridge Psychology Research Ethics Committee (The Administrator of the Cambridge Psychology Research Ethics Committee, School of the Biological Sciences, 17 Mill Lane, Cambridge, UK; +44 (0)1223 76689; Cheryl.Torbett@admin.cam.ac.uk), ref: Pre.2019.100
Interventional randomized controlled trial
Primary study design
Secondary study design
Randomised controlled trial
Patient information sheet
Not available in web format, please use the contact details to request a patient information sheet.
The online and lab parts of the study will be conducted simultaneously.
Online Study: Mixed design, with 3x2 between-subjects conditions (3 availability conditions x 2 shelf fullness conditions), and one within-subjects condition (manipulation level)
Participants are asked to estimate the percentage of sales – as a measure of perceived popularity – accounted for by healthier (over less-healthy) products displayed in a series of photos. For each set of food and drink options, participants will be randomised to one of six groups to see displays that contain:
Group 1: 75% healthier & 25% less-healthy options, fuller shelves;
Group 2: 50% healthier & 50% less-healthy options, fuller shelves;
Group 3: 25% healthier & 75% less-healthy options, fuller shelves;
Group 4: 75% healthier & 25% less-healthy options, emptier shelves;
Group 5: 50% healthier & 50% less-healthy options, emptier shelves;
Group 6: 25% healthier & 75% less-healthy options, emptier shelves
The primary endpoint is the perceived percentage of sales accounted for by healthier (over less-healthy) options.
Randomisation for the online study will be conducted via the inbuilt randomisation procedures on the Qualtrics platform.
Lab Study: Between-subjects design, with 4 groups (2 availability x 2 tray fullness conditions)
Participants are offered a snack food at the end of a different study. They are randomly allocated to one of four conditions, which vary in terms of the mix of healthier and less healthy foods offered and the fullness of the tray on which the snacks are offered:
Group 1: 75% healthier & 25% less-healthy options, full tray;
Group 2: 25% healthier & 75% less-healthy options, full tray;
Group 3: 75% healthier & 25% less-healthy options, half-empty tray;
Group 4: 25% healthier & 75% less-healthy options, half-empty tray.
The primary endpoint is the selection of a healthier (over less-healthy) option.
Random numbers will be generated – using Stata - to assign participant numbers to each study condition.
Primary outcome measure
Perceived percentage of sales of healthier (over less-healthy) products measured using the slider questions on the Qualtrics platform
Food selection, measured by observing the selection of food (healthier or less healthy) from the tray during the study
Secondary outcome measures
Selection of products during the study
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Adults aged over 18 years
2. Currently residing within the UK
Target number of participants
Online Study: 2,340; Lab Study: 279
Total final enrolment
Participant exclusion criteria
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
University of Cambridge
Behaviour and Health Research Unit Institute of Public Health University Forvie Site Robinson Way
Funding Body Type
private sector organisation
Funding Body Subtype
Results and Publications
Publication and dissemination plan
1. Planned submission of the main results of this study for publication in a peer-reviewed journal
2. Dissemination of the results to the public, policy makers and other researchers through targeted social media
IPD sharing statement
The data sharing plans for the current study are unknown and will be made available at a later date.
Intention to publish date
Participant level data
To be made available at a later date
Basic results (scientific)