Peer Effects in Workplace Health

Last registered on September 10, 2021


Trial Information

General Information

Peer Effects in Workplace Health
Initial registration date
September 08, 2021

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
September 10, 2021, 12:23 PM EDT

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



Primary Investigator


Other Primary Investigator(s)

Additional Trial Information

On going
Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
There exists a large literature studying peer effects in economics yet little research on how peer effects in health can occur in the workplace. This experiments aims to derive causal estimate of workplace peer effects and to study the underlying mechanisms. The setting is a large company in the US and the context is the fall vaccination campaign.
External Link(s)

Registration Citation

Barankay, Iwan. 2021. "Peer Effects in Workplace Health." AEA RCT Registry. September 10.
Experimental Details


The interventions are happening in the context of a yearly flu vaccine drive. There will be two set of interventions.
In interventions (A) we split all employees who did not opt out of communications into three groups. The first group is receives the standard message, comparable to how it was used in prior years at the company. The second group receives a message that tells them that taking vaccinations will inspire others to do the same, a passive peer effect. The third group receives a message that encourages them to get other people to get vaccinated, an active peer effect.
Concurrently we randomly select 200 people at the firm who are told that if they get vaccinated before a deadline $100 will be donated to a charity.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Primary outcome is individual level flu vaccination status (binary).
Primary Outcomes (explanation)
This variable is drawn from the company wellness program that is linked to employees health records.

Secondary Outcomes

Secondary Outcomes (end points)
Company wellness program points, LDL, Blood pressure, glucose level, ASCVD risk, medical expenses without Rx, Rx medical expenses, attrition. Sub-population analysis by race, ethinicity, job tenure, and social preferences
Secondary Outcomes (explanation)
company wellness program points, LDL, blood pressure, glucose level, ASCVD risk, medical expenses with and without Rx are derived from the companies wellness program that is linked with health records. Attrition, race, ethnicity and job tenure is based on HR data. Social preferences is based on measure from online experiments conducted during the second half of 2020.

Experimental Design

Experimental Design
Part A. Employees at the company are randomized into four groups and receive different messages encouraging them to get a flu vaccine.
This tests whether being informed of peer effects (group 2) or being encouraged to influence others (group 3) affects the flu vaccination rate compared to the control group.
Part B. 200 randomly selected employees receive a message telling them that when vaccinated an amount will be donated to a charity. The outcome of interest is the flu vaccination rate of the peers of the recepient of the message compared to those employees where the peers did not receive a message.
Experimental Design Details
Randomization Method
Part A: Ranomization with Stata's runiform routine that allocates a number of 0, 1, or 2 to each employee at the company thus allocating them to the control message, the second group or the third group.
Part B: independently from the randomization in part A 200 employees are drawn using SAS's survey select routine stratified by age, company wellness program status level, and hierarchy tier in the company.
Randomization Unit
Randomization is at the individual level.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
Sample size: planned number of observations
Sample size (or number of clusters) by treatment arms
Part A: Control (7,198), First group (7,198), Second Group (7,198), Third group (7,199)
Part B: Treatment (200)
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Measurable vaccination rate is 0.56 in the control arm. This is based on flu shot vaccination rates from the past year. With a power of 0.8 the minimum detectable effect (delta) will be an increase of 2.39 percentage points (0.5839 - 0.56) With a power of 0.9 the minimum detectable effect will be an increase of 2.71 percentage points (0.5871 - 0.56)

Institutional Review Boards (IRBs)

IRB Name
University of Pennsylania
IRB Approval Date
IRB Approval Number


Post Trial Information

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Is the intervention completed?
Data Collection Complete
Data Publication

Data Publication

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Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials