Stress and In-Group Preferences

Last registered on June 17, 2019


Trial Information

General Information

Stress and In-Group Preferences
Initial registration date
February 21, 2019

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
February 24, 2019, 7:48 PM EST

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

Last updated
June 17, 2019, 2:25 PM EDT

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



Primary Investigator

Stanford 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. June 17.
Former Citation
Haushofer, Johannes et al. 2019. "Stress and In-Group Preferences." AEA RCT Registry. June 17.
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
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.

Institutional Review Boards (IRBs)

IRB Name
Princeton University
IRB Approval Date
IRB Approval Number
Analysis Plan

There is information in this trial unavailable to the public. Use the button below to request access.

Request Information


Post Trial Information

Study Withdrawal

There is information in this trial unavailable to the public. Use the button below to request access.

Request Information


Is the intervention completed?
Data Collection Complete
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials