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Diverse Committees

Last registered on February 10, 2020


Trial Information

General Information

Diverse Committees
Initial registration date
February 10, 2020

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 10, 2020, 10:49 AM EST

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


Primary Investigator

Uni Essex

Other Primary Investigator(s)

PI Affiliation
Kings College London
PI Affiliation
University of Essex

Additional Trial Information

In development
Start date
End date
Secondary IDs
A popular argument in favour of diversity in committees is that different groups might have access to different information. Hence, by omitting some groups this information might be lost to the committee.

We study committee decision making when there is possible correlation between the information held by members of the same group. If people fail to properly account for this correlation, then decision making in homogeneous (non-diverse) committees might be substantially worse. We provide theoretical predictions for four scenarios differing by whether information of members of the same group is correlated or not and whether members of different groups have identical preferences over outcomes or not and then test these using a laboratory experiment.
External Link(s)

Registration Citation

Hughes, Niall, Friederike Mengel and Zia Ul Hassan Khan. 2020. "Diverse Committees." AEA RCT Registry. February 10.
Experimental Details


Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
(i) Committee decisions (dummy indicating whether committee decision was correct); (ii) individual guesses (dummy indicating whether they were correct)
Primary Outcomes (explanation)
Our primary question is whether heterogenous committees make better decisions than homogenous committes measured by the variables indicated above.

Secondary Outcomes

Secondary Outcomes (end points)
Expected payoffs of committee members of different types.
Secondary Outcomes (explanation)
When preferences are different, then “correct” decisions (in the sense of matching the state) might not be the same as (ex ante) “preferred” decisions. Hence for this case we will also look at the expected payoffs of committee members.

Experimental Design

Experimental Design
Participants in our experiment are randomly assigned to either of two groups, S or T. They answer a pre-experimental questionnaire, play 12 rounds of the game described below and then answer a post-experimental questionnaire.
In each round of the experiment participants will (i) receive a signal, (ii) discuss (via a chat window) with their committee members and (iii) vote in committees of three participants about which of two urns (yellow or purple) was selected at the beginning of the round.
Treatments differ according to whether the signal received at stage (i) is correlated among members of the same group or not. They also differ by the payments received when voting correctly. In some treatments both groups prefer the purple state. In some treatments preferences are not aligned with one group preferring the purple state and one group the yellow state.
Experimental Design Details

Randomization Method
participants register for sessions without knowing what session is about. assignment of sessions to treatments is done in the office by computer.
Randomization Unit
experimental session
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
32 sessions.
Sample size: planned number of observations
864 individuals.
Sample size (or number of clusters) by treatment arms
8 sessions per treatment.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
As there are no prior studies with effect sizes on which to base our choice of sample size we proceeded as follows. We conducted two sessions (54 participants) of the treatment with correlated information and identical preferences across the two groups. In these two sessions we detected an effect size of 0.107 for the committee level variable and 0.083 for the individual level variable. We then conducted a power analysis using these effect sizes. Our chosen sample of 216 participants per treatment across 8 clusters allows us to detect a committee level effect of 0.107 with 78.47% power (at the 5% level) and the individual level effect of 0.083 with 88.45% power again at the 5% level. As show up for experimental sessions can be unpredictable, we cannot commit to the exact sample size of 216 participants per treatment. Instead, we propose to proceed running sessions until the threshold of 216 participants has been reached. If we achieve the same show up as in the initial sessions this would mean running 8 sessions (clusters) per treatment.

Institutional Review Boards (IRBs)

IRB Name
University of Essex Social Sciences Ethics Subcommittee
IRB Approval Date
IRB Approval Number
Analysis Plan

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Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
October 14, 2021, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
October 14, 2021, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
225 participants in treatments AL-IND and AL-CORR, 219 participants in MIS-IND and 222 participants in MIS-CORR.
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
Final Sample Size (or Number of Clusters) by Treatment Arms
225 participants in treatments AL-IND and AL-CORR, 219 participants in MIS-IND and 222 participants in MIS-CORR
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Hughes, Niall and Khan, Zia UH and Mengel, Friederike, Diversity in Committees (June 29, 2023). Available at SSRN: or

Reports & Other Materials