Do charitable appeals in bargaining crowd out voluntary donations?

Last registered on October 01, 2021


Trial Information

General Information

Do charitable appeals in bargaining crowd out voluntary donations?
Initial registration date
September 28, 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
October 01, 2021, 3:44 PM EDT

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


Primary Investigator

University of Hamburg

Other Primary Investigator(s)

PI Affiliation
University of Hamburg

Additional Trial Information

In development
Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
We test whether charitable offers within bargaining situations crowd out voluntary donations to charity. Inspired by bundles of private
and public goods in the marketplace, we implement variants of ultimatum games that allow for voluntary donations after the initial offer has been accepted. We test whether the option of linking charitable donations to offers in the bargaining situation increase the final provision of the public good. A special focus of the analyses will lie on gender differences as men and women were found to respond differently to social information in previous research.
External Link(s)

Registration Citation

Lange, Andreas and Claudia Schwirplies. 2021. "Do charitable appeals in bargaining crowd out voluntary donations?." AEA RCT Registry. October 01.
Experimental Details


We design the experiment as an ultimatum game where we allow for donations to charity (by proposer and responder) after the offer has been accepted (ex post giving).
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
total donations (as a share of the endowment) and the total donation rate
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
bundling rate (proportion of proposers who use the bundling channel), bundled donations (as share of the endowment), donation rate (proportion of players who give ex post) for proposers and responders, gender differences for all outcome variables, gender differences in donating ex post conditional on the bundled donation d > 0 or d = 0
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
This experiment takes up the question whether linking private and public goods within bundled offers actually increases the provision of public goods or just opens a channel that fully crowds out otherwise existing voluntary donations. We run the experiment with Amazon MTurk workers. We implement variants of the ultimatum game to explore bundling and voluntary donations. In our first treatment (control), we link the standard ultimatum game with an ex post option to donate parts of the payoff to charity (UGdon). The second treatment (intervention) introduces this ex post donation option in a “prosocial ultimatum game” (PSUGdon), where the proposer can suggest a split between himself, the responder and a charitable donation. Ex post donations in UGdon and PSUGdon can be viewed as direct evidence for utility derived from the public good or warm-glow motives. The use of bundled offers in PSUGdon, on the other hand, can be driven by
strategic motivations in order to generate acceptance by responders. We are primarily interested in how this bundling channel impacts the additional voluntary donation and thus the total provision level of the public good. We also explore gender differences, especially in donations conditional on being confronted with a donation in the bargaining situation.
Experimental Design Details
Randomization Method
We randomly match proposers and responders together using a module for urn draws provided by SoSci Survey (, a tool for online surveys, which we use for implementing the decisions on Amazon MTurk.
Randomization Unit
We randomize at the individual level
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
200 individuals per role (proposer/responder) and treatment
Sample size: planned number of observations
800 individuals
Sample size (or number of clusters) by treatment arms
400 individuals per treatment
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
In a pretest, we received total donations of 0.08 (of the $10 endowment) with a donation rate of 35%. Based on Chi2-tests, the minimum detectable effect size is 0.09283 for the proportion of total donations and 0.1378 for the donation rate.

Institutional Review Boards (IRBs)

IRB Name
Alexander Szimayer
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