Stress and In-Group Preferences
Last registered on February 24, 2019


Trial Information
General Information
Stress and In-Group Preferences
Initial registration date
February 21, 2019
Last updated
February 24, 2019 7:48 PM EST

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Primary Investigator
Bocconi University
Other Primary Investigator(s)
PI Affiliation
Northwestern University
PI Affiliation
Harvard University
PI Affiliation
Princeton University
Additional Trial Information
In development
Start date
End date
Secondary IDs
We describe the analysis plan for a laboratory experiment that will examine the effects of hydrocortisone administration on in-group preferences, specifically coethnic preference. The study will be conducted with individuals living in Nairobi, Kenya who are from the Luo, Kikuyu, Luhya and Kamba ethnic groups. Using a double-blind procedure, participants are randomly administered either a placebo or an identical-looking 20 mg dose of hydrocortisone, a drug that increases the levels of the stress hormone cortisol. Participants complete several experimental tasks in which they are paired with individuals that vary in their gender, age group, and ethnicity. We outline the study design, the outcomes of interest, and the econometric strategy for the analysis.
External Link(s)
Registration Citation
Haushofer, Johannes et al. 2019. "Stress and In-Group Preferences." AEA RCT Registry. February 24.
Experimental Details
Intervention Start Date
Intervention End Date
Primary Outcomes
Primary Outcomes (end points)
The primary question of interest is whether participants display more in-group preference, and in particular coethnic preference, when they receive the hydrocortisone pill. The key outcomes of interest are behavior in the lab experiments and several survey questions. E.g. for the dictator game the outcome of interest is the amount that player 1 sends to player 2; for the choose your dictator game the outcome of interest is which player, Person A or Person B, the participant chooses as their player 1; and for the trust game, the amount sent to the other player as a player 1 and the amount returned as a player 2. The various measures and games are described in detail in the attached pre-analysis plan.
Primary Outcomes (explanation)
Secondary Outcomes
Secondary Outcomes (end points)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
Participants are randomly assigned to be in either a treatment group or control group. Participants in the treatment group receive 20 mg of oral hydrocortisone. Participants in the placebo group receive a placebo pill that is identical in appearance to the hydrocortisone pill.
Experimental Design Details
Not available
Randomization Method
Before each session begins, we generate participant IDs, each of which is randomly assigned to the treatment or placebo group. It is double blind.
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
750 treatment 750 control
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
We are aiming for a sample size of 1,500 participants. Conservative power calculations indicate that this will allow detecting effect sizes of 0.15 SDs or less.
IRB Name
Princeton University
IRB Approval Date
IRB Approval Number
Analysis Plan

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