What motives increase prosocial behavior? An experiment on blood donation

Last registered on March 18, 2025
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Pre-Trial

Trial Information

General Information

Title
What motives increase prosocial behavior? An experiment on blood donation
RCT ID
AEARCTR-0015541
Initial registration date
March 11, 2025

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
March 18, 2025, 10:16 AM EDT

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

Locations

Country
Italy
Region
Sardinia

Primary Investigator

Name
Gabriele Ballicu
Affiliation
University of Cagliari
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Other Primary Investigator(s)

PI Name
Vittorio Pelligra
PI Affiliation
University of Cagliari
Contact Investigator

Additional Trial Information

Status
Completed
Start date
2023-05-24
End date
2023-06-13
Keywords
Behavior, Health
Additional Keywords
field experiment, blood donation, frame
JEL code(s)
C93, D64, H41, I18
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
Although numerous surveys have explored why people donate blood, no research has compared the strength of these motivations with actual donation rates. To fill this gap, we conducted a field experiment with 24,839 college students, sending them messages targeting different motivations (social norms, empathy, guilt, and self-interest motives). We tracked both their willingness to donate and their actual donations, and found a consistent gap between intention and action. In addition, responses varied significantly depending on the messages received. These findings have important policy implications, informing targeted advertising campaigns and helping to identify the right audiences for blood donation initiatives.
External Link(s)
the study was preregistered also on OSF

Registration Citation

Citation
Ballicu, Gabriele and Vittorio Pelligra. 2025. "What motives increase prosocial behavior? An experiment on blood donation." AEA RCT Registry. March 18. https://doi.org/10.1257/rct.15541-1.0
Sponsors & Partners

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Experimental Details

Interventions

Intervention(s)
We have five treatments of the online questionnaire (run between subjects), each with a standard structure of questions (regarding demographic and blood information, as well as questions about attitudes and beliefs on blood donation). Afterward, we ask the subjects if they want to donate blood during the blood drive (this serves as the proxy for intention to donate). This last message differs across groups:

A simple message (T0) that asks participants to be contacted by a voluntary blood donation association.
A norm-framed message (T1) that incorporates the effect of social, descriptive, and moral norms, combined with reciprocity.
A burden-to-not-donate framed message (T2) that combines reluctant altruism with guilty-regret emotion and inequality aversion.
An empathy-framed message (T3) that uses the identifying victim effect, with a story of two people (a male and a female) needing blood donations.
A hedonistic-framed message (T4) with self-interested motives (such as a free day from work, scholarships, free medical check-ups, and health benefits).
Intervention (Hidden)
Intervention Start Date
2023-05-24
Intervention End Date
2023-06-13

Primary Outcomes

Primary Outcomes (end points)
Blood donation (tracked with a code)
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Intention to donate (answer in the questionnaire)
Beliefs on incentives about blood donation (answer in the questionnaire)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
Subjects receive an email explaining the importance of gathering information and opinions about blood donation, especially to improve blood donation organizations in the region. Another email follows with a survey that offers a potential financial reward upon completion. We explain that they can participate in a survey, which takes about five minutes, conducted in collaboration with AVIS (the largest blood bank organization in Italy), to analyze public opinions on blood donation. We also remind them about the possibility of winning a monetary prize and that they can book a day to donate blood.

We make it clear that it is essential to remember the unique code generated after completing the survey. However, we emphasize that the probability of winning the prize is entirely independent of the decision to donate blood, as participants will be randomly assigned to receive the prize. The only requirement to win the prize is completing the questionnaire, which is crucial to prevent biasing people's behavior by motivating them to donate due to a "lottery incentive."

To encourage participation, we incentivize completion to increase the sample size. We award 20 prizes of 100 euros ten days after the blood drives, selecting twenty randomly from those who complete the survey. To prevent people from filling out the questionnaire multiple times to increase their chances of winning or obtaining more codes, they must log in with their institutional email to enter the lottery. Personal and questionnaire data are collected on separate sites and stored in distinct datasets to protect participants' privacy and anonymity and to avoid any potential experimental demand effects.
Experimental Design Details
Randomization Method
Randomization done by LimeSurvey
Randomization Unit
Unit of observation for this study is at the individual level.
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
No cluster for treatment
Sample size: planned number of observations
At least 2000 subjects
Sample size (or number of clusters) by treatment arms
at least 400 subjects per group
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials

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IRB

Institutional Review Boards (IRBs)

IRB Name
ethics committee of the University of Cagliari
IRB Approval Date
2023-06-01
IRB Approval Number
Prot. n. 0112536 of 01/06/2023 - [Classif. II/9]
Analysis Plan

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Post-Trial

Post Trial Information

Study Withdrawal

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Intervention

Is the intervention completed?
Yes
Intervention Completion Date
June 13, 2023, 12:00 +00:00
Data Collection Complete
Yes
Data Collection Completion Date
June 13, 2023, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
Was attrition correlated with treatment status?
No
Final Sample Size: Total Number of Observations
6,762 students (3,872 valid after data cleaning)
Final Sample Size (or Number of Clusters) by Treatment Arms
760 control, 749 T1, 809 T2, 779 T3, 775 T4
Data Publication

Data Publication

Is public data available?
No

Program Files

Program Files
No
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials