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NUDGES IN EXERCISE COMMITMENT CONTRACTS
Last registered on July 20, 2015
View Trial History

Pre-Trial

Trial Information
General Information
Title
NUDGES IN EXERCISE COMMITMENT CONTRACTS
RCT ID
AEARCTR-0000784
Initial registration date
July 20, 2015
Last updated
July 20, 2015 1:53 PM EDT
Location(s)
Country
United States of America
Region
Primary Investigator
Name
Jay Bhattacharya
Affiliation
Stanford University
Contact Primary Investigator
Other Primary Investigator(s)
PI Name
Jeremy Goldhaber-Fiebert
PI Affiliation
Stanford University
Contact Investigator
PI Name
Alan Garber
PI Affiliation
Harvard University
Contact Investigator
Additional Trial Information
Status
Completed
Start date
2010-10-01
End date
2012-04-30
Keywords
Health
Additional Keywords
behavioral economics, physical activity, nudges, commitment contract
JEL code(s)
D6, I1, I12
Secondary IDs
Abstract
We consider the welfare consequences of nudges and other behavioral economic devices to encourage exercise habit formation. We analyze a randomized trial of nudged exercise commitment contracts in the context of a time-inconsistent intertemporal utility maximization model of the demand for exercise. The trial follows more than 4,000 people seeking to make exercise commitments. Each person was randomly nudged towards making longer (20 weeks) or shorter (8 weeks) exercise commitment contracts.

Our empirical analysis shows that people who are interested in exercise commitment contracts choose longer contracts when nudged to do so, and are then more likely to meet their pre-stated exercise goals. People are also more likely to enroll in a subsequent commitment contract after the original expires if they receive a nudge for a longer duration initial contract. Our theoretical analysis of the welfare implications of these effects shows conditions under which nudges can reduce utility even when they succeed in the goal of promoting habitual exercise.
External Link(s)
Registration Citation
Citation
Bhattacharya, Jay, Alan Garber and Jeremy Goldhaber-Fiebert. 2015. "NUDGES IN EXERCISE COMMITMENT CONTRACTS." AEA RCT Registry. July 20. https://doi.org/10.1257/rct.784-1.0.
Former Citation
Bhattacharya, Jay et al. 2015. "NUDGES IN EXERCISE COMMITMENT CONTRACTS." AEA RCT Registry. July 20. https://www.socialscienceregistry.org/trials/784/history/4820.
Sponsors & Partners
Experimental Details
Interventions
Intervention(s)
In the experiment, we randomly assign the user to an 8, 12, or 20-week default duration for the contract, which can be modified with a simple mouse click. The user also chooses a contracted exercise frequency. We do not randomize the default frequency seen by the user. Next, the user designates the financial penalty for every failed week, which can take a value of zero or any positive number of dollars. Finally, the user can designate a referee to confirm whether she or he has successfully completed each week of exercise.

For each user-initiated contract (signed or not), we collect information on the date, the randomized nudge, the choices made about contract features (duration, frequency, penalties, referee, etc.), whether the contract was signed, and if the contract was signed, the user’s weekly exercise performance. Each week that was not a success resulted in a deduction from the user’s credit card for the contracted penalty amount. Additionally, we collect baseline information about each user’s age, sex, and country (determined by their IP address) along with any prior contracts with stickK.com.
Intervention Start Date
2010-10-01
Intervention End Date
2012-04-30
Primary Outcomes
Primary Outcomes (end points)
(1) Likelihood of signing a commitment contract
(2) Changes in chosen contract features
(3) Likelihood of exercising successfully during the contract
(4) Likelihood of signing a subsequent commitment contract
Primary Outcomes (explanation)
N/A
Secondary Outcomes
Secondary Outcomes (end points)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
In the experiment, we randomly assign the user to an 8, 12, or 20-week default duration for the contract, which can be modified with a simple mouse click. The user also chooses a contracted exercise frequency. We do not randomize the default frequency seen by the user. Next, the user designates the financial penalty for every failed week, which can take a value of zero or any positive number of dollars. Finally, the user can designate a referee to confirm whether she or he has successfully completed each week of exercise.

For each user-initiated contract (signed or not), we collect information on the date, the randomized nudge, the choices made about contract features (duration, frequency, penalties, referee, etc.), whether the contract was signed, and if the contract was signed, the user’s weekly exercise performance. Each week that was not a success resulted in a deduction from the user’s credit card for the contracted penalty amount. Additionally, we collect baseline information about each user’s age, sex, and country (determined by their IP address) along with any prior contracts with stickK.com.
Experimental Design Details
Randomization Method
Randomization done by computer
Randomization Unit
Individual session on stickK.com
Was the treatment clustered?
No
Experiment Characteristics
Sample size: planned number of clusters
N/A
Sample size: planned number of observations
8809 contracts
Sample size (or number of clusters) by treatment arms
2952 in 8-week nudge arm
2981 in 12-week nudge arm
2876 in 20-week nudge arm
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
N/A
Supporting Documents and Materials
IRB
INSTITUTIONAL REVIEW BOARDS (IRBs)
IRB Name
Stanford University
IRB Approval Date
2009-10-22
IRB Approval Number
03H08
Analysis Plan
Post-Trial
Post Trial Information
Study Withdrawal
Intervention
Is the intervention completed?
No
Is data collection complete?
Yes
Data Collection Completion Date
Final Sample Size: Number of Clusters (Unit of Randomization)
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
Final Sample Size (or Number of Clusters) by Treatment Arms
Data Publication
Data Publication
Is public data available?
No
Program Files
Program Files
Reports and Papers
Preliminary Reports
Relevant Papers