Do social norms play a role in explaining the impact on food selection of increasing the proportion of healthier food available?

ISRCTN ISRCTN10512908
DOI https://doi.org/10.1186/ISRCTN10512908
Secondary identifying numbers Pre.2019.100
Submission date
24/01/2020
Registration date
31/01/2020
Last edited
07/01/2021
Recruitment status
No longer recruiting
Overall study status
Completed
Condition category
Other
Prospectively registered
Protocol
Statistical analysis plan
Results
Individual participant data
Record updated in last year

Plain English summary of protocol

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
rachel.pechey@phc.ox.ac.uk
(updated 07/01/2021, previously: rachel.pechey@medschl.cam.ac.uk)

Contact information

Dr Rachel Pechey
Scientific

Nuffield Department of Primary Care Health Sciences
University of Oxford
Radcliffe Primary Care Building
Radcliffe Observatory Quarter
Woodstock Rd
Oxford
OX2 6GG
United Kingdom

ORCiD logoORCID ID 0000-0002-6558-388X
Email rachel.pechey@phc.ox.ac.uk

Study information

Study designInterventional randomized controlled trial
Primary study designInterventional
Secondary study designRandomised controlled trial
Study setting(s)Other
Study typePrevention
Participant information sheet Not available in web format, please use the contact details to request a patient information sheet.
Scientific titleIncreasing the relative availability of healthier vs. less-healthy food: Exploring the role of social norms
Study objectivesOnline Study:
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

Lab Study:
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)
Ethics approval(s)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
Health condition(s) or problem(s) studiedUnhealthy diet
InterventionThe 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)
Online Study:
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)
Lab Study:
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.
Intervention typeBehavioural
Primary outcome measureOnline Study:
Perceived percentage of sales of healthier (over less-healthy) products measured using the slider questions on the Qualtrics platform

Lab Study:
Food selection, measured by observing the selection of food (healthier or less healthy) from the tray during the study
Secondary outcome measuresOnline study:
Selection of products during the study
Overall study start date01/12/2019
Completion date31/08/2020

Eligibility

Participant type(s)Healthy volunteer
Age groupAdult
Lower age limit18 Years
SexBoth
Target number of participantsOnline Study: 2,340; Lab Study: 279
Total final enrolment2480
Key inclusion criteria1. Adults aged over 18 years
2. Currently residing within the UK
Key exclusion criteriaNone
Date of first enrolment03/02/2020
Date of final enrolment16/03/2020

Locations

Countries of recruitment

  • England
  • United Kingdom

Study participating centre

University of Cambridge
Behaviour and Health Research Unit
Institute of Public Health
University Forvie Site
Robinson Way
Cambridge
CB2 0SR
United Kingdom

Sponsor information

University of Cambridge
University/education

Trinity Lane
Cambridge
CB2 1TN
England
United Kingdom

Phone +44 (0)1223 333543
Email research_governance@medschl.cam.ac.uk
Website http://www.cam.ac.uk/
ROR logo "ROR" https://ror.org/013meh722

Funders

Funder type

Charity

Wellcome Trust
Private sector organisation / International organizations
Location
United Kingdom

Results and Publications

Intention to publish date31/12/2020
Individual participant data (IPD) Intention to shareNo
IPD sharing plan summaryData sharing statement to be made available at a later date
Publication and dissemination plan1. 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 planThe data sharing plans for the current study are unknown and will be made available at a later date.

Editorial Notes

07/01/2021: The following changes were made to the trial record:
1. The contact details were updated.
2. The plain English summary was updated to reflect these changes.
11/05/2020: The following changes have been made:
1. Recruitment is no longer suspended.
2. The recruitment end date has been changed from 30/06/2020 to 16/03/2020.
3. The final enrolment number has been added.
09/04/2020: Due to current public health guidance, recruitment for this study has been paused.
28/01/2020: Trial’s existence confirmed by Cambridge Psychology Research Ethics Committee.