Illinois Workplace Wellness Study

Last registered on March 28, 2022


Trial Information

General Information

Illinois Workplace Wellness Study
Initial registration date
July 11, 2016

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 11, 2016, 11:23 AM EDT

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

Last updated
March 28, 2022, 5:01 PM EDT

Last updated is the most recent time when changes to the trial's registration were published.


Primary Investigator

University of Chicago

Other Primary Investigator(s)

PI Affiliation
University of Illinois at Urbana-Champaign
PI Affiliation
University of Illinois at Urbana-Champaign
PI Affiliation
University of Illinois at Urbana-Champaign

Additional Trial Information

Start date
End date
Secondary IDs
NIH R01AG050701
Prior work
This trial does not extend or rely on any prior RCTs.
Workplace wellness programs have become a $6 billion industry and are widely touted as a way to improve employee well-being, reduce health care costs by promoting prevention, and increase workplace productivity. Yet, there is little rigorous evidence available to support these claims, partly because the voluntary nature of these programs means that participants may differ from nonparticipants for reasons unrelated to the causal effects of the wellness program. We will implement a randomized control trial to identify the effects of incentives on wellness program participation, produce causal estimates of the effect of wellness programs on health outcomes, determine what kinds of employees benefit from wellness programs the most, and test for the presence of peer effects in wellness participation.
External Link(s)

Registration Citation

Jones, Damon et al. 2022. "Illinois Workplace Wellness Study." AEA RCT Registry. March 28.
Former Citation
Jones, Damon et al. 2022. "Illinois Workplace Wellness Study." AEA RCT Registry. March 28.
Sponsors & Partners


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Experimental Details


Our treatment consists of a baseline survey among all control and treatment group members. Treatment group members will then be offered the opportunity to participate in a biometric screening and health risk assessment (biometric screening + HRA), and -- conditional on completing an biometric screening + HRA -- up to two, semester-long wellness programs (e.g. walking challenge, active living class, smoking cessation hotline). Treatment group members will be offered varying levels of cash reward for completing the biometric screening + HRA ($0, $100, $200), and an additional cash reward for completing each wellness activity ($25, $75), for a total of 6 treatment cells. An additional treatment group will feature a clustered treatment, based on self-reported peer groups measured in the baseline survey. Follow-up surveys and biometric screenings will be administered one year later, among a subset of control and treatment group members.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
(1) biometric screening and HRA completion; (2) wellness activity participation and completion; (3) health utilization based on medical claims data; (3) absenteeism based on human resources (HR) data; (4) biometric health screening data; (5) health risk assessment data; (6) self-reported health status on baseline survey; (7) self-reported health status on follow-up survey; (8) expectations of health status prior to screening
Primary Outcomes (explanation)
Medical claims data: total costs, costs to employer, inpatient visits, outpatient visits, ER visits, diagnosis codes
Biometric data: height, weight, waist circumference, resting blood pressure, total cholesterol, total cholesterol ratio, HDL cholesterol, LDL cholesterol, triglycerides, glucose levels
Health Risk Assessment data: self-reported wellness, health status, nutrition, healthy activities, desire to improve health, preventative health measures
Baseline Survey data: self-reported health status, healthy activities, preventative health measures
Health expectations: expected weight, height, cholesterol, glucose, blood pressure, body mass index

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We will draw a sample of all benefit-eligible employees at the university (approximately 12,000). An invitation will be sent to each employee, asking them to participate in a baseline survey. Employees will receive a gift card of $30 for completing the survey. Respondents to the baseline survey will comprise our core sample.

The core sample will be divided randomly into either a control group, or one of 4 treatment groups, Treatments A - D. Treatment groups A, B and C will receive a cash incentive of $0, $100, and $200, respectively, for completing the biometric screening + HRA. Within each group, half of the members will also be offered $25 for each of up to two, semester-long wellness activities that are completed during the year. The other half will be offered $75 for completing up to two, semester-long wellness activities during the school year.

The final treatment group, D, will feature a clustered design. The baseline survey will elicit information about workplace social networks. We will use standard methods to map those networks among those employees that do respond to the baseline survey. Provided that we are able identify a sufficient number of non-overlapping, local neighborhoods, we will systematically assign a share of neighborhood members to either the control group or the treatments of groups A, B and C with equal probability. Treatment group D will feature a higher share of control group members in a given social network than members of treatment groups A, B and C.

Upon completion of the baseline survey and treatment group assignment, employees will be invited to schedule a biometric screening. Once the biometric screening is completed, an online HRA will be made available for participants. Following completion of the HRA, participants will be allowed to enroll in up to two wellness activities.

One year later, members of the control and treatment groups will be invited to complete an additional follow-up survey and biometric survey. Incentives will be increased in the follow-up period in order to minimize attrition. Participants will be offered either $25 or $35 dollars for completing the follow-up survey, and either $150 or $250 for completing a follow-up biometric screening. In order to minimize attrition, these incentives may be modified based on information gained from the first year of the experiment.

Our ability to implement the peer-effects design, i.e. treatment group D, depends on the structure of social networks in our data. We cannot observe these prior to collecting baseline survey data. Once we have done so, we will be able to do preliminary power analysis. In the event that including a peer effects group significantly reduces our statistical power, we will eliminate treatment group D, and focus on an individual level design.
Experimental Design Details
Randomization Method
Randomization will be done on an office computer using Stata's pseudo-random number generator with a preset seed of 11.
Randomization Unit
Our peer effects design will randomize treatment at the self-reported social network level.
For the rest, treatment will be randomized at the individual level, and stratified by age, gender, and employee class.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
no peer effect design: 6,000 employees
peer effect design: 5,600 employee/social networks
Sample size: planned number of observations
6,000 employees
Sample size (or number of clusters) by treatment arms
no-peer effect design: 2,700 employees control; 1,100 employees treatment group A; 1,100 employees treatment group B; 1,100 employees treatment group C
peer effect design: 2,300 employees control; 900 employees treatment group A; 900 employees treatment group B; 900 employees treatment group C; 200 social networks treatment group D
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Participation MDE: - 5.7 percentage points (baseline 50% participation) when comparing groups B + C to group A - 6.6 percentage points if we are separately comparing group B to group A, and group C to group A. Selection Regression MDE: approximately 3.8 percentage points, for an attribute that is held by 40% of the population. Short-Run Effects Regression MDE: - 0.61 for BMI (mean = 26.3%, SD = 3.9%) - 1.21 for Systolic blood pressure (mean = 120, SD = 7.5) - 0.97 for diastolic blood pressure (mean 80, SD = 6) - 0.23 for absenteeism (mean = 4, SD = 2)

Institutional Review Boards (IRBs)

IRB Name
Social and Behavioral Sciences Institutional Review Board at the University of Chicago
IRB Approval Date
IRB Approval Number
IRB Number: 16-0728
IRB Name
NBER Institutional Review Board
IRB Approval Date
IRB Approval Number
IRB# 15_105
IRB Name
Office for the Protection of Research Subjects, University of Illinois at Urbana-Champaign
IRB Approval Date
IRB Approval Number
IRB Protocol Number: 16456
Analysis Plan

Analysis Plan Documents

Analysis Plan

MD5: 08e821579d15fff3b2da7649973cc09f

SHA1: a8f2316f39a6b8e56c908bfc3cc5ce23f116e0e3

Uploaded At: March 28, 2022


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Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
April 26, 2018, 12:00 +00:00
Data Collection Complete
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Workplace wellness programs cover over 50 million U.S. workers and are intended to reduce medical spending, increase productivity, and improve well-being. Yet limited evidence exists to support these claims. We designed and implemented a comprehensive workplace wellness program for a large employer and randomly assigned program eligibility and financial incentives at the individual level for nearly 5,000 employees. We find strong patterns of selection: during the year prior to the intervention, program participants had lower medical expenditures and healthier behaviors than nonparticipants. The program persistently increased health screening rates, but we do not find significant causal effects of treatment on total medical expenditures, other health behaviors, employee productivity, or self-reported health status after more than two years. Our 95% confidence intervals rule out 84% of previous estimates on medical spending and absenteeism.
Damon Jones, David Molitor, Julian Reif, What do Workplace Wellness Programs do? Evidence from the Illinois Workplace Wellness Study, The Quarterly Journal of Economics, , qjz023,

Reports & Other Materials