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Encouraging Healthy Nutrition Purchases in an Online Grocery Setting using Experimental Economics.
Last registered on July 02, 2018

Pre-Trial

Trial Information
General Information
Title
Encouraging Healthy Nutrition Purchases in an Online Grocery Setting using Experimental Economics.
RCT ID
AEARCTR-0002325
Initial registration date
October 06, 2017
Last updated
July 02, 2018 9:26 PM EDT
Location(s)
Region
Primary Investigator
Affiliation
Duke-NUS Medical School
Other Primary Investigator(s)
Additional Trial Information
Status
Completed
Start date
2017-10-09
End date
2018-05-01
Secondary IDs
Abstract
The important role that diet plays in health and disease is well established, as is its association with rising rates of obesity—a phenomenon of increasing concern in Singapore. Changes in lifestyle patterns, including a movement towards a more western-style diet with an emphasis on pre-packaged and fast food, have contributed to the upward trend in weight. This study aims to test two competing approaches for calorie labelling in efforts to reduce total calories purchased. In Arm 1 (termed across category labelling) a low calorie logo will be displayed on the 20% of products on the web store that are lowest in calories per serving. Arm 2 will display this logo on the 20% of products that are lowest in calories per serving within each product category (termed within category labelling). Arm 3 is the Control condition which will not display any logo on any products.

For our primary outcome, we hypothesize that the proportion of labelled products (or those that would have been labelled if not in control arm) purchased in each intervention arm will be greater than in control.

For secondary hypotheses we expect the following ordering across the three (Control, Within category, Across category) arms:
1. total calories (adjusted for household size): C > A > W
2. calories per serving: C > A > W
3. calories per dollar spent: W > A > C
4. total dollars spent (adjusted for household size) : W > A > C


External Link(s)
Registration Citation
Citation
Finkelstein, Eric . 2018. "Encouraging Healthy Nutrition Purchases in an Online Grocery Setting using Experimental Economics.." AEA RCT Registry. July 02. https://doi.org/10.1257/rct.2325-3.0.
Former Citation
Finkelstein, Eric . 2018. "Encouraging Healthy Nutrition Purchases in an Online Grocery Setting using Experimental Economics.." AEA RCT Registry. July 02. http://www.socialscienceregistry.org/trials/2325/history/31429.
Sponsors & Partners

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Experimental Details
Interventions
Intervention(s)
This study relies on a fully functional and customizable web grocery store with over 1,800 products. For the Control condition, the participants will not be exposed to the lower calorie logo when they shop. For Intervention 1 (Across Category Labelling), the participant will see the lower calorie logo applied to the 20% of foods with the lowest calories per serving across all food categories. For intervention 2 (Within Category Labelling), the participant will see the lower calorie logo applied to the 20% of foods with the lowest calories per serving within each food category.
Intervention Start Date
2017-10-09
Intervention End Date
2018-04-27
Primary Outcomes
Primary Outcomes (end points)
- Proportion of products that are designated as labelled in the interventions
Primary Outcomes (explanation)
Secondary Outcomes
Secondary Outcomes (end points)
1. Total calories (adjusted for household size)
2. Calories per serving
3. Calories per dollar spent
4. Total dollars spent (adjusted for household size)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
Overview of website: For this study an online grocery store was developed that contains over 1800 products commonly purchased in local supermarkets. The products available for purchase include foods from many different categories such as dairy products, snacks, processed meats and soft drinks. The web-based grocery store was designed to mirror an actual web-based grocery store in look and feel. All products include a picture of the item, current retail price, the Lower Calorie logo (where applicable), and other package size and nutrition information currently required for products in Singapore. The online grocery store features a grocery cart that shows the items purchased. The NUS Online Collection Facility payment system has been integrated with the online grocery store for participants to make payments for purchased foods.

Study design: This will be a crossover study design with all participants exposed once to 3 shopping conditions (1xControl, 1xIntervention 1 (I1), 1x Intervention 2(I2)) in random order. The total study duration for each participant is 3 weeks, with each participant spending 1 week in each shopping condition.

For the Control condition the participants will not be exposed to the lower calorie logo. For Intervention 1 (Across), the participant will see the lower calorie logo applied to foods with the lowest calories per serving across all food categories. For intervention 2, the participant will see the lower calorie logo applied to the 20% of foods with the lowest calories per serving within each food category. These foods will be tagged with the ‘Lower Calorie’ logo.

Participants will be asked to shop once a week during each of the 3 weeks of the study, and will therefore shop for a total of 3 times during the study. This will include 1 shop within each shopping condition (control, I1, and I2). Participants will purchase and receive at least 1 and up to 3 of their grocery orders. This ensures that purchases will be an accurate reflection of their actual shopping experience.

Since there are 3 shopping conditions (Control, I1, and I2) and the specific weeks that the participant’s shopping trips will be pre-determined for purchase (but unknown to participants), each participant will be randomly assigned at baseline to 1 of 6 groups that vary the sequence of shopping conditions.

For each shop there will be a minimum spend of SGD50 and a maximum spend of SGD250.
A minimum spend ensures that participants complete a typical weekly grocery order. A maximum spend is to make the study more manageable given foods will need to be reordered and delivered. The grocery orders that participants purchase will be ordered by Duke-NUS using RedMart, a popular online grocery store in Singapore, and RedMart will deliver the grocery items. The store was created using products currently available on the RedMart website to allow us to repurchase from a single location.

At the end of the study participants who have completed all 3 shops as instructed will receive a $75 RedMart e-Voucher worth $75 payment that can be redeemed against any products on RedMart.
Experimental Design Details
Randomization Method
Simple randomization.
Randomization Unit
Individual.
Was the treatment clustered?
No
Experiment Characteristics
Sample size: planned number of clusters
168 individuals. No clustering but each individuals will shop 3 times, once for each arm.
Sample size: planned number of observations
168 x 3 = 504
Sample size (or number of clusters) by treatment arms
This will be a crossover study design with all participants exposed once to all 3 shopping conditions (1xControl, 1xIntervention 1 (I1), 1x Intervention 2(I2)) . We have calculated the sample size of a 3 (interventions) x 3 (periods) cross-over design. Participants will be block-randomized into 1 of 6 allocation sequence possible, with a block size of 6.

We have used the sample size calculator from Harvard (http://hedwig.mgh.harvard.edu/sample_size/js/js_crossover_quant.html) and applied the following options:

- 0.025 of significance level to make two comparisons at the 5% level of statistical significance
- 90 % of statistical power
- Relative effect size (difference in means divided by standard deviation) of 0.3 (small)
- Selected the standard deviation of the difference between the two values for the same patient as we will analyze a model in differences
- 20% attrition rate
Rounding up to the closest multiple of 6 to keep the design exactly balanced suggests that we need a sample size of 168 completes.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
IRB
INSTITUTIONAL REVIEW BOARDS (IRBs)
IRB Name
National University of Singapore (NUS) Institutional Review Board
IRB Approval Date
2017-04-10
IRB Approval Number
N-17-011
Post-Trial
Post Trial Information
Study Withdrawal
Intervention
Is the intervention completed?
Yes
Intervention Completion Date
April 27, 2018, 12:00 AM +00:00
Is data collection complete?
Yes
Data Collection Completion Date
April 27, 2018, 12:00 AM +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
146 Individuals
Was attrition correlated with treatment status?
No
Final Sample Size: Total Number of Observations
437 sales orders
Final Sample Size (or Number of Clusters) by Treatment Arms
146 observations from control, 146 observations from intervention arm I, 145 observations from intervention arm II.
Data Publication
Data Publication
Is public data available?
No

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Program Files
Program Files
No
Reports, Papers & Other Materials
Relevant Paper(s)
REPORTS & OTHER MATERIALS