Prosocial motivation for COVID-19 vaccination

Last registered on September 12, 2021


Trial Information

General Information

Prosocial motivation for COVID-19 vaccination
Initial registration date
September 10, 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 12, 2021, 11:18 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)

PI Affiliation
PI Affiliation
UC Berkeley Haas

Additional Trial Information

On going
Start date
End date
Secondary IDs
Prior work
This trial is based on or builds upon one or more prior RCTs.
We test whether prosocial behavior in economic games predicts self-reported COVID-19 vaccination.
External Link(s)

Registration Citation

Charness, Gary, David Levine and Lucas Reddinger. 2021. "Prosocial motivation for COVID-19 vaccination." AEA RCT Registry. September 12.
Experimental Details


Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Prosocial behavior in economic games / whether (and when) individuals report having taken a COVID-19 vaccine dose.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We registered our study “Can targeted messages reduce COVID-19 vaccination hesitancy?” as AEARCTR-0007478 and conducted the trial in April 2021. In August 2021 we followed a sample of these respondents to collect additional participant characteristics.

We sought to attain a follow-up sample balanced between those reporting that they had taken a COVID-19 vaccine dose and those reporting that they had not. To this end, we randomly sampled half of participants who in April said that they intended to take a vaccine dose as soon as possible; we randomly sampled half of participants who were not classified as being a member of any segment of interest; we sampled the entirety of all other subjects. This provided a sample of 2441 participants from the 3668 qualified participants in April.

Of the multitude of characteristics we solicited from participants in August, we have only analyzed one. We tabulated whether (and when) respondents reported having taken a vaccine dose. Our results:

Have you taken a COVID-19 vaccine dose?
No 336 (56%)
Yes, in... 262 (44%)
April 86 (14%)
May 77 (13%)
June 41 (7%)
July 35 (6%)
August 18 (3%)
Unsure 4 (1%)
Prefer not to say 4 (1%)

We have thus achieved a sample well-balanced on our primary characteristic of interest.

We now will follow these participants yet again in an incentivized online session titled “Survey with decision-making for bonus payment.” This session will be run under a different survey account than previous sessions to eliminate any possible framing effects. Each participant is given $4 to play a variety of games that relate to pro-social preferences. We include two games to check participant comprehension. Our regression analyses will include the covariates collected in August. We will test whether pro-social behavior in our incentivized games predicts self-reported vaccination.
Experimental Design Details
Randomization Method
Randomization done in office by a computer. Only sampling is randomized, as we have no intervention.
Randomization Unit
Individual. Only sampling is randomized, as we have no intervention.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
600 individuals.
Sample size: planned number of observations
600 individuals.
Sample size (or number of clusters) by treatment arms
Our study is only observational, but uses unique sampling methods as explained in the experimental design.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Institutional Review Boards (IRBs)

IRB Name
UCSB Human Subjects Committee
IRB Approval Date
IRB Approval Number


Post Trial Information

Study Withdrawal

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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