NUDGES IN EXERCISE COMMITMENT CONTRACTS

Last registered on July 20, 2015
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Pre-Trial

Trial Information

General Information

Title
NUDGES IN EXERCISE COMMITMENT CONTRACTS
RCT ID
AEARCTR-0000784
Initial registration date
July 20, 2015

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
July 20, 2015, 1:53 PM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Locations

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, Alan Garber and Jeremy Goldhaber-Fiebert. 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

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Intervention

Is the intervention completed?
No
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, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials