Minimum Contribution Mechanism

Last registered on March 27, 2023


Trial Information

General Information

Minimum Contribution Mechanism
Initial registration date
November 23, 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
November 29, 2021, 8:19 AM EST

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

Last updated
March 27, 2023, 4:22 PM EDT

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


Primary Investigator


Other Primary Investigator(s)

Additional Trial Information

On going
Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
This study examines a public goods mechanism
External Link(s)

Registration Citation

Neligh, Nathaniel. 2023. "Minimum Contribution Mechanism." AEA RCT Registry. March 27.
Experimental Details


Participants will engage in several public goods games with different mechanisms
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Contributions under each mechanism
Mechanism Efficiency
Primary Outcomes (explanation)
Efficiency taken in the strong sense (maximizing sum of payoffs)

Secondary Outcomes

Secondary Outcomes (end points)
Beliefs about mechanism efficiency
Secondary Outcomes (explanation)
Which mechanism do people expect to have higher payoffs in?

Experimental Design

Experimental Design
Participants will engage in several public goods games with different mechanisms
Experimental Design Details
This experiment will be done with the standard UTK economics laboratory population. Participants who
have previously engaged with public goods games will be excluded to avoid contamination of the pool.
This protocol involves an experiment where players play public goods games on an online survey

99 Online Players will be given a link to a Qualtric survey which they will complete on their own.

200 In person players will come to the UTK experimental economics lab accross approximately 10 sessions. They will see the experiment already open on screen when they are seated.

During the experiment, a player will play a sequence of public goods game. In these games, players are
matched in groups of 3 and given a budget. Each player is asked to offer some of their budget to a public
good. The public good produces tokens based on total contributions and then distributes them between
players. Contributing a token is generally good for the group since the public good generally creates more
tokens than it takes in, but contributing is bad for the individual, since they don’t get all of the benefit
their contribution creates.
A player will play 6 games throughout the experiment. These games differ in how the offers made by
players are converted into contributions and in whether the budgets are homogenous or not.
In half the rounds, budgets will be the same for all players while in the other half they will be different. At
the beginning of the experiment, a player is assigned a position that they will keep throughout the
experiment. A player’s position will dictate what budget they will receive in rounds where the budgets are
There are 3 distinct mechanisms used in the experiment to convert offers into contributions. The
voluntary contribution mechanism converts offers directly into contributions. The provision point
mechanism converts offers into contributions only if total offers exceed a certain amount. The novel
minimum contribution mechanism has every player contribute an amount equal to the lowest offer made.

Note that there is no feedback between rounds and no real-time interaction. Instead payoffs are
generated by matching players randomly into groups after the fact (at the end of the session for in person participants). This prevents issues with getting many participants online and playing at the same time and makes it harder for players to converge to an equilibrium when coordination issues are present.

Analysis will focus on comparing how the efficiency of outcomes and total offers compare between
mechanisms in differing budget conditions. This experiment is primarily concerned with comparing the
performance of the provision point and minimum contribution mechanisms with the voluntary contribution
mechanism acting as a type of control. Currently, the provision point mechanism is commonly used in
public goods situations, so any improvement could be valuable.
Based on the theory, the minimum contribution mechanism should perform better, and its advantage
should be greater in conditions of heterogeneous budget constraints.
Randomization Method
By computer online or in person
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
300 people
Sample size: planned number of observations
300 people
Sample size (or number of clusters) by treatment arms
100 people per position
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials

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Institutional Review Boards (IRBs)

IRB Name
Univeristy of Tennessee Knoxville Institutional Review Board
IRB Approval Date
IRB Approval Number
UTK IRB-21-06573-XM


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
February 28, 2022, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
February 28, 2022, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
99 individuals
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
594 contribution choices
Final Sample Size (or Number of Clusters) by Treatment Arms
Within Subjects Design
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials