Social norm nudges in supermarket trolleys to promote vegetable purchases

ISRCTN ISRCTN39440735
DOI https://doi.org/10.1186/ISRCTN39440735
Secondary identifying numbers None
Submission date
05/09/2018
Registration date
13/09/2018
Last edited
27/07/2020
Recruitment status
No longer recruiting
Overall study status
Completed
Condition category
Nutritional, Metabolic, Endocrine
Prospectively registered
Protocol
Statistical analysis plan
Results
Individual participant data

Plain English summary of protocol

Background and study aims
Low vegetable consumption is a considerable health problem worldwide. A diet low in vegetables is associated with an increased risk of becoming overweight or obese, and other health related chronic diseases. Supermarkets have a major influence on daily food intake, because most foods are purchased in supermarkets. Therefore, supermarkets can be a suitable setting for health interventions to stimulate vegetable purchases. Nudging is an effective strategy to stimulate vegetable purchases. Nudging is simply defined as changes in the environment to alter people’s behavior in a predictable way, without forbidding any options. In this study we investigated the effectiveness of two nudging strategies in supermarket trolleys to stimulate vegetable purchases among supermarket customers.

Who can participate?
Supermarket customers with a shopping trolley and a cash receipt can participate in this study.

What does the study involve?
The intervention in this study consists of a green inlay in shopping trolleys with social norm messages about vegetable purchases of other customers of the supermarket. This will cover the bottom half of each trolley, indicating a place to put vegetables. The intervention days of the study are the days on which the green inlay will be used in the shopping trolleys, and the control days will be the days where there are no inlays (regular shopping trolleys). Cash receipts will be collected and surveys will be conducted among customers after they have paid for their groceries.

What are the possible benefits and risks of participating?
There are no known benefits or risks to participants taking part in this study.

Where is the study run from?
Vrije Universiteit Amsterdam (The Netherlands)

When is the study starting and how long is it expected to run for?
January 2017 to June 2018

Who is funding the study?
Vrije Universiteit Amsterdam (The Netherlands)

Who is the main contact?
Marlijn Huitink
m.huitink@vu.nl

Contact information

Mrs Marlijn Huitink
Scientific

De Boelelaan 1085
Amsterdam
1081 HV
New Zealand

ORCiD logoORCID ID 0000-0002-5303-9668

Study information

Study designInterventional non-randomised study
Primary study designInterventional
Secondary study designNon randomised study
Study setting(s)Other
Study typeOther
Participant information sheet No participant information sheet available
Scientific titleSocial norm nudges in shopping trolleys to promote vegetable purchases: a supermarket experiment in a deprived urban area in the Netherlands
Study objectivesWe investigated the effectiveness of two nudging strategies in shopping trolleys on the amount of vegetables purchased in a Dutch supermarket in a disadvantaged urban area. The nudges are as follows:
1. A place for vegetables
2. Social norm communication
Ethics approval(s)The study was conducted according to the ethical standards declared in the Helsinki declaration of 1975, as revised in 2000. Active verbal informed consent was given by all customers. The Medical Ethics Committee of the Vrije Universiteit Amsterdam confirmed that this study does not apply to the Medical Research Involving Human Subjects Act (WMO), due to the nature of the measurements (sales data and anonymous questionnaires distributed among adults). Therefore, approval was waived.
Health condition(s) or problem(s) studiedVegetable sales
InterventionThe intervention consisted of three green inlays, indicating the space where customers can place their vegetables, each with a different social norm message about vegetable purchases of other customers from the participating supermarket. Customers on the intervention days received a shopping trolley with a green inlay with one of the three different social norm messages. The intervention was tested during two days (Friday evening and Saturday morning). The control days used the usual shopping trolleys with no green inlay. Cash receipts were collected and surveys conducted among customers after they had paid for their groceries.
Intervention typeBehavioural
Primary outcome measureVegetables purchased (in grams and in items), assessed at the end of each study day over the two-week study period using:
1. Examination of cash receipts
2. Surveys with customers after they had paid for their groceries
Secondary outcome measuresThe following were assessed using oral surveys in the supermarket after customers had paid for their groceries over the two-week study period:
1. Customer characteristics:
1.1. Sex
1.2. Age category
1.3. Highest obtained education
2. Customer grocery behaviour characteristics:
2.1. Number of persons and days for which groceries were purchases
2.2. Use of a shopping list or not
2.3. Place customers purchased vegetables most often
2.4. If customers thought that they purchased less, more or the same amount of vegetables during this shopping trip as they usually would
Overall study start date01/01/2017
Completion date01/06/2018

Eligibility

Participant type(s)All
Age groupAll
SexBoth
Target number of participants244
Total final enrolment244
Key inclusion criteriaSupermarket customers in Amsterdam with a shopping trolley and a cash receipt
Key exclusion criteria1. Not willing to consent to having photograph of cash receipt taken
2. Purchased groceries for more than 12 persons for one day
Date of first enrolment12/05/2018
Date of final enrolment20/05/2018

Locations

Countries of recruitment

  • Netherlands

Study participating centre

Vrije Universiteit Amsterdam
De Boelelaan 1085
Amsterdam
1081 HV
Netherlands

Sponsor information

Vrije Universiteit Amsterdam
University/education

De Boelelaan 1085
Amsterdam
1081 HV
Netherlands

Website https://www.vu.nl/nl/
ROR logo "ROR" https://ror.org/008xxew50

Funders

Funder type

Not defined

Vrije Universiteit Amsterdam

No information available

Results and Publications

Intention to publish date11/09/2018
Individual participant data (IPD) Intention to shareNo
IPD sharing plan summaryNot expected to be made available
Publication and dissemination planPublication of a research article with submission planned in 2018
IPD sharing planThe data sharing plans for the current study are unknown and will be made available at a later date

Study outputs

Output type Details Date created Date added Peer reviewed? Patient-facing?
Results article results 01/08/2020 27/07/2020 Yes No

Editorial Notes

27/07/2020: The following changes have been made:
1. Publication reference added.
2. The final enrolment number has been added from the reference.