Pilot Randomized Controlled Trial Testing the Influence of Front-Of-Pack Sugar Warning Labels on Food Demand
Last registered on January 18, 2019

Pre-Trial

Trial Information
General Information
Title
Pilot Randomized Controlled Trial Testing the Influence of Front-Of-Pack Sugar Warning Labels on Food Demand
RCT ID
AEARCTR-0003800
Initial registration date
January 17, 2019
Last updated
January 18, 2019 3:26 AM EST
Location(s)
Region
Primary Investigator
Affiliation
Duke-NUS Medical School
Other Primary Investigator(s)
Additional Trial Information
Status
Completed
Start date
2017-08-01
End date
2017-08-31
Secondary IDs
Abstract
This pilot study aims to test two competing approaches of front-of-pack labelling for sugar content. We developed an online grocery store containing over 1,800 food and beverages commonly purchased at local supermarkets to test the effects of these labels on consumer choice. This web store was designed to mirror an actual online grocery store in appearance. The study was designed as a Randomized Controlled Trial (RCT) where consumers were randomized and asked to hypothetically shop in one of three versions of an online grocery store; 1) no FOP label (control), 2) a graphical high-in-sugar label shaped like a stop sign, or 3) a text-based warning label. For the intervention arms (Arms 2 and 3), the labels will be displayed below images of “high-in-sugar” products. A food item is classified as a “high-in-sugar” product if it is among the top 20% of products—within its product category—with the highest sugar percentage (defined as amount of sugar per 100 g). A beverage is classified as a “high-in-sugar” product if it contains at least 10 g per 100 ml (i.e. 10%) of sugar. Given the strongly worded language similar to tobacco warning labels that are used in the text-based health warning label, we hypothesized that the proportion of labelled (or targeted for labelling in Control Arm) products among respondents would be the largest in Control and smallest in the warning label condition (primary outcome). We hypothesized a similar ordering for secondary outcomes, including total sugar purchased, sugar (g) per dollar spent, and total spending.

The pilot study is a part of the larger project titled: Multiphase Evaluation of Healthier Choice Symbol (HCS) Logo (Project Number: NMRC/HSRG/0060/2016). Following the completion of this pilot study, the procedures and results of the pilot will also be used to refine and develop a larger scale Randomized-Controlled Trial (RCT).
External Link(s)
Registration Citation
Citation
Finkelstein, Eric. 2019. "Pilot Randomized Controlled Trial Testing the Influence of Front-Of-Pack Sugar Warning Labels on Food Demand." AEA RCT Registry. January 18. https://www.socialscienceregistry.org/trials/3800/history/40310
Experimental Details
Interventions
Intervention(s)
In this study, we use an experimental web-based grocery store to pilot test two different theory- and evidence-based ‘FOP’ warning labels aimed to reduce purchases of high-in-sugar products. The first label we consider is an English language version similar to the one used in Chile that shows a black stop sign (Arm termed SS) with the words high-in-sugar in the center. The second label we consider is a text-based health warning label (Arm termed TW), which is similar to labels considered in several municipalities in the US and also resembles the warning label on cigarettes, but without the accompanying graphics.

We identified products to receive a warning label based on the percentage of sugar as compared to other products within the food category. We chose a within category approach to mirror the approach taken for the HCS program. A food product is classified as high-in-sugar if it is among the top 20% of products with the highest sugar content per 100 g within the food category. A beverage is classified as high-in-sugar if it contains at least 10 g per 100 ml (i.e. 10%) of sugar. Using this approach, 20% of food within each food category and 27% of beverages were defined as high-in-sugar and received the corresponding label for the SS and TW arms.
Intervention Start Date
2017-08-01
Intervention End Date
2017-08-31
Primary Outcomes
Primary Outcomes (end points)
The primary outcome of interest is the proportion of high in sugar products purchased.
Primary Outcomes (explanation)
Secondary Outcomes
Secondary Outcomes (end points)
The following secondary outcomes are measured:
• Total sugar purchased (in g) per shopping trip,
• Sugar purchased per dollar spent (in grams per $),
• Total spending (in $) given that high-in-sugar products tend to be less expensive, and
• Total expenditure on high-in-sugar products ($).
Secondary Outcomes (explanation)
• Total sugar purchased (in g) per shopping trip is calculated as the sum of all sugar purchased in the participants' sales orders
• Sugar purchased per dollar spent (in grams per $) is the amount of sugar purchased for every dollar spent
• Total spending (in $) is calculated as the sum cost of all products purchased in the sales order
• Total expenditure on high-in-sugar products ($) is calculated as the sum cost of all products targeted for labelling in the sales order.
Experimental Design
Experimental Design
For this pilot trial, an online grocery store (named NUSMart) was developed that contains over 1,800 food and beverages commonly purchased at local supermarkets. The products available for purchase include food and beverages from various categories such as dairy products, snacks, processed meats, and soft drinks. This web-based grocery store was designed to mirror an actual web-based grocery store in look and feel. All products include a picture(s) of the item, current retail price, the high in sugar or warning label (where applicable), and other package size and nutrition information currently required for food and beverages sold in Singapore. The online grocery store also features a grocery cart that shows the items purchased and the ability to add and remove items accordingly.

Participants completed all study-related procedures online. Prospective participants were directed, by a survey company, to the study website (https://nusmart.duke-nus.edu.sg/pilot-diet/) and asked to read and complete an online information sheet & consent form. Only potential participants from their existing database who are Singapore Residents aged 21 and above had access to the study. If a participant declines to give his or her consent, the applicant was informed that he/she is not eligible to join the study.

Each participant was then randomly assigned to see only one of the three versions of the website, where the difference was the presence (or absence) of a label graphically displayed on select products, and the type of label seen: either a stop-sign label (Arm 2) or Text-based health warning label (Arm 3).

While participants were made aware that there are three versions of NUSMart and that they would be experiencing only one, the exact details of the arms were not revealed to ensure validity of results.

Participants were randomly assigned into one of the three arms:
Arm 1: no-label control
Arm 2: high in sugar label
Arm 3: text-based health warning label

For the control condition (Arm 1), the participants will not be exposed to any logo. For the two intervention arms (Arms 2 and 3), participants saw a label below the images of “high-in-sugar” products. A food item is classified as a “high-in-sugar” product if it is among the top 20% of products—within its product category—with the highest sugar percentage (defined as amount of sugar per 100 g). A beverage is classified as a “high-in-sugar” product if it contains at least 10 g per 100 ml (i.e. 10%) of sugar.

Participants were requested to shop as they would normally shop in a typical grocery shopping experience for their families and spend a minimum of 50 Singapore dollars and maximum of 250 Singapore dollars. Participants were not charged and did not receive any groceries. Each participant was asked to shop only once and took 10–30 minutes to complete the shopping session.
Experimental Design Details
Randomization Method
Randomization done in office by a computer program.
Randomization Unit
Individual.
Was the treatment clustered?
No
Experiment Characteristics
Sample size: planned number of clusters
510 individuals.
Sample size: planned number of observations
510 observations.
Sample size (or number of clusters) by treatment arms
170 per arm.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
We powered the study to detect differences of at least 3 percentage points across arms in terms of the percentage of high in sugar products purchased. Assuming a common group standard deviation of 0.83 (based on unpublished data from ongoing studies), an alpha of 0.05 and power of 0.8, and adjusted for multiple comparisons, a sample of 170 participants per arm was required to test our hypotheses.
IRB
INSTITUTIONAL REVIEW BOARDS (IRBs)
IRB Name
National University of Singapore (NUS) Institutional Review Board
IRB Approval Date
2017-07-19
IRB Approval Number
S-17-172
Post-Trial
Post Trial Information
Study Withdrawal
Intervention
Is the intervention completed?
Yes
Intervention Completion Date
August 31, 2017, 12:00 AM +00:00
Is data collection complete?
Yes
Data Collection Completion Date
August 31, 2017, 12:00 AM +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
512 individuals.
Was attrition correlated with treatment status?
No
Final Sample Size: Total Number of Observations
512 individual observations.
Final Sample Size (or Number of Clusters) by Treatment Arms
175 arm 1 (control), 167 arm 2 (high-in-sugar stop sign), 170 arm 3 (Text-based health warning label).
Data Publication
Data Publication
Is public data available?
No

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Program Files
Program Files
No
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Preliminary Reports
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