Subsidizing Quantity Donations: Matches, Rebates, and Discounts Compared

Last registered on November 20, 2018


Trial Information

General Information

Subsidizing Quantity Donations: Matches, Rebates, and Discounts Compared
Initial registration date
November 19, 2018

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
November 19, 2018, 10:54 PM EST

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

Last updated
November 20, 2018, 6:21 AM EST

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



Primary Investigator

Heidelberg University

Other Primary Investigator(s)

PI Affiliation
Monash University
PI Affiliation
Texas A&M University
PI Affiliation
Heidelberg University

Additional Trial Information

Start date
End date
Secondary IDs
We define a class of donations termed quantity donations and present evidence from an online field experiment on whether well-known results from the literature on subsidizing charitable giving generalize to this class. In the quantity donation, donors choose how many units of a charitable good to fund, rather than the amount of money to give. With this small modification, we find that rebate and matching subsidies are equally effective in raising funds, which contrasts the common result of matches being superior. This outcome masks a higher likelihood of giving under rebates and larger donations under matches. A third subsidy type framed as discount off the per-unit price of the charitable good is just as effective. Our findings challenge the generalizability of established results on subsidy instruments and emphasize the role of small changes in the donation environment.
External Link(s)

Registration Citation

Diederich, Johannes et al. 2018. "Subsidizing Quantity Donations: Matches, Rebates, and Discounts Compared." AEA RCT Registry. November 20.
Former Citation
Diederich, Johannes et al. 2018. "Subsidizing Quantity Donations: Matches, Rebates, and Discounts Compared." AEA RCT Registry. November 20.
Experimental Details


Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Charity receipts, i.e. average number of units of the charitable good that can be provided by the charity from the average donation per subject
Primary Outcomes (explanation)
Outcome variable 1: Average number of nutritional packages selected by individuals, without accounting for any subsequent subsidy (checkbook giving). Outcome variables 2-4 directly follow from this. Outcome variable 2 translates subjects' choices (variable 1) into out-of-pocket expenses, which correspond to the notion of checkbook giving in a standard expenditure donation experiment. Hence, variable 2 is variable 1 evaluated at the nominal price at which the package was offered to subjects, that is, $0.50 in all rebate and match treatments and $0.33 ($0.25) in the price discount treatment with low (high) subsidy rate. Variable 3 is individual net expenses after rebates have been accounted for. Variable 4 is the contributions of nutritional packages including the match (charity receipts in number of packages), i.e. the number of packages the charity will be able to fund from the received donations. Variable 5: If variable 4 is multiplied by $0.50, the result corresponds to the charity receipts in dollars, a common focus in expenditure donation experiments. Variable 6: average charity receipts conditional on being a donor (intensive margin of giving). Variable 7: the fraction of donors, i.e.~subjects who give at least one package (extensive margin of giving).

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We adapt the real-donation dictator game introduced by Eckel and Grossman (1996) and subsequently applied to compare subsidy types (Eckel and Grossman, 2003; Davis and Millner, 2005; Davis, 2006; Eckel and Grossman, 2006a,b). In the standard version of the game, subjects decide how much of their endowment to hold and how much to pass to a charity. This choice corresponds to an expenditure donation. In our variant of the game, subjects decide how many units of the charitable good to fund at a given price, using their endowment. This choice corresponds to a quantity donation.

Our variant of the game requires a charitable good or service that is easily quantifiable. We approached a relief organization which makes extensive use of quantity donation calls in fundraising campaigns. Among their activities, we chose the treatment of malnourished children in a certain area of South Sudan as this service offered practical units and prices for our experiment. The children are treated in two ``bush clinics'' operated by the relief organization. Treating one child for one month using a special nutritional paste and high energy cookies requires a donation of $15. We divided this number into practical units of nutritional packages per child and day which implies a price (required donation) of $0.50 per package. In the donation task of the online experiment, subjects were introduced to the charity, the charitable good, and its marginal provision cost to the charity.

There are one baseline condition and six interventions. In the control condition, no subsidy was applied. Subjects were endowed with $2 and chose how many units of the charitable good to fund at a price of $0.50. The six treatment conditions were derived by applying the three subsidy types at two different levels each. We framed the rebate conditions as a 50\% (33\%) rebate, so that $0.25 ($0.17) per unit provided would be added to the final reward. Match conditions were framed as a match of each (every two) unit(s) the subject provides at no additional costs. Discount conditions were framed as a possibility of providing units for $0.25 ($0.33) apiece. For all subsidy types, subjects were informed that the subsidy is provided by ``a third party", subjects facing the discount subsidy learned that the reduced price results from a third party funding the remaining cost of $0.25 ($0.17) per package. The two subsidy levels imply effective prices of $0.33 and $0.25. Note however that for the 1:2 match, the effective price per package is not constant, since only every second unit provided by the subject induces an additional subsidy payment.

Treatment conditions were administered in both a between-subjects (BS) and a within-subjects (WS) design to two different subject samples. In the BS design, subjects were introduced to a specific subsidy condition or the control and had to choose the desired number of units from a drop-down menu. In the WS design, all seven conditions were listed in random order and subjects entered, for each condition, an integer number indicating their desired number of units. Subjects were informed that one of the conditions would be randomly selected through a lottery and implemented.

We recruited subjects from an online labor market, Amazon's Mechanical Turk (AMT), restricted to US residents. In the posted task, interested workers were informed that they would earn $2 for answering a 20-minutes academic survey on several topics. Donations were mentioned as one of the topics, but the real-donation dictator game was not particularly salient compared to other survey elements, so it is unlikely that subjects considered the donation task as the main subject of investigation. Interested workers followed a link which directed them to the survey containing the experiment.
Experimental Design Details
Randomization Method
Randomization is done by the survey system (Qualtrics)
Randomization Unit
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
Planned about 140 subjects in within-subject design, about 450 subjects in between-subject design, roughly equal splic across the 7 treatment cells (control plus six interventions).
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Institutional Review Boards (IRBs)

IRB Name
IRB Approval Date
IRB Approval Number


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
October 04, 2015, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
October 04, 2015, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
718 subjects (complete observations out of 759 recruited subjects)
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
718 subjects (complete observations out of 759 recruited subjects)
Final Sample Size (or Number of Clusters) by Treatment Arms
113 subjects in within-subject design, 558 subjects in between-subject design. Treatment cells in between-subject design: 83, 71, 85, 90, 58, 80, and 91 subjects.
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials