Inequality and Moral Universalism

Last registered on April 23, 2026

Pre-Trial

Trial Information

General Information

Title
Inequality and Moral Universalism
RCT ID
AEARCTR-0018372
Initial registration date
April 14, 2026

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
April 23, 2026, 9:18 AM EDT

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

Locations

Region

Primary Investigator

Affiliation
Maastricht University

Other Primary Investigator(s)

PI Affiliation
College of William & Mary

Additional Trial Information

Status
In development
Start date
2026-04-15
End date
2026-12-31
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
In a new experiment, we conduct a controlled laboratory study to examine the relationship between different forms of inequality, namely inequality of outcomes and inequality of opportunities, and moral universalism. The study also investigates the mechanisms through which these forms of inequality may influence moral universalism. Specifically, we test whether positional competition, rank-related anxiety, and trust underlie the effect of inequality on moral universalism. The study is implemented in a controlled laboratory setting with incentivized tasks.
External Link(s)

Registration Citation

Citation
Martorano, Bruno and Laura Metzger. 2026. "Inequality and Moral Universalism." AEA RCT Registry. April 23. https://doi.org/10.1257/rct.18372-1.0
Experimental Details

Interventions

Intervention(s)
The aim of the study is to examine the relationship between inequality and moral universalism. The intervention consists of experimentally varying exposure to inequality in a controlled laboratory setting. Participants are randomly assigned to one of three conditions: inequality of outcomes, inequality of opportunities, or a control condition with equal pay. In the inequality of outcomes condition, participants are randomly assigned a low (2 EUR) or high (8 EUR) bonus. In the inequality of opportunities condition, bonus allocation depends on gender. In the control condition, all participants receive the same bonus. Following the intervention, participants complete a series of incentivized tasks designed to measure behavioral responses to inequality and to capture potential mechanisms, including positional competition, rank-related concerns, and generalized trust.
Intervention Start Date
2026-04-16
Intervention End Date
2026-06-30

Primary Outcomes

Primary Outcomes (end points)
We will estimate the impact of different types of inequality on moral universalism, as well as on two behavioral outcomes: willingness to sign a petition and participation in a volunteering task aimed at reducing inequality.
Primary Outcomes (explanation)
- Moral Universalism. We measure universalism taking inspiration from Cappelen et al. (2025) and Enke et al. (2024). Specifically, we ask participants a hypothetical question. "Suppose you have earned 1,000 EUR, but must give it away to two other people. You cannot keep any of the money to yourself. In all decisions, assume that both people have the same everyday standard of living. You can allocate the money between both people any way you wish?". The same question is repeated for several ingroup-members such as: (i) their family, (ii) a friend, (iii) a neighbour, (iv) someone who shares their religious beliefs, or (v) ethnic background, and (vi) a random stranger from their country.
To measure the effect of inequality on moral universalism, we construct an index by averaging participants’ allocations across all in-group categories and then inverting the resulting score. The final index ranges from 0 to 1000, where higher values indicate greater moral universalism and lower values indicate stronger in-group favouritism. The reason for creating an index is that the six variables are correlated with one another; treating them as independent hypotheses would overstate the effective number of tests, as they capture closely related dimensions of a common moral orientation. Using the index helps to increase precision and reduce noise by reducing the risk of spurious inference due to multiple testing.
- Petition. As a behavioral outcome, participants are given the opportunity to sign a petition advocating for increased action against inequality. The outcome is a binary indicator equal to one if the participant chooses to sign the petition and zero otherwise. This design allows us to examine whether exposure to inequality differentially affects support for policies targeting distinct domains of inequality.
- Volunteering exercise. Lasty, participants are invited to a volunteering exercise, where they can spend additional time (not be remunerated), to perform an effort task with the purpose of gaining additional money to support the activity of a well-established charity that fights to reduce inequality in all its forms. Specifically, they are presented with a series of small tasks. In each task, they are asked to select a specific number using a slider. For each page they completed accurately, they donate 0.1 EUR to the charity selected. They can complete up to 3 tasks in total, and they are asked before each one whether they would like to continue. Participation is completely voluntary, and they can stop at any time by clicking "No". We consider two alternative outcomes: a binary variable equal to one if the participant agrees to participate, and zero otherwise; and a continuous variable capturing performance in the task.

Secondary Outcomes

Secondary Outcomes (end points)
We will examine whether positional competition, rank-related anxiety, and trust mediate the effect of inequality on moral universalism.
Secondary Outcomes (explanation)
To measure individual competitiveness, participants perform a standard effort task in which they are rewarded for correctly counting zeros in a line of numbers under time pressure. The outcomes of this task (i.e., the number of correct lines) are also used to measure two key mechanisms: positional competition and anxiety.
- Positional competition. Participants choose how to allocate two correct lines between an in-group recipient (same gender and ranking group) and an out-group recipient (different session and separate ranking). The outcome is a binary variable equal to one if the participant allocates to the out-group recipient, indicating greater sensitivity to ranking pressure. This measure is complemented by a second task. Participants choose between two options in a hypothetical group task with friends: (i) helping everyone, which improves group outcomes but may worsen their relative rank, or (ii) helping only themselves. The outcome is a binary variable equal to one if the participant chooses “Help only yourself,” indicating a lower willingness to help others when rank incentives are present.
- Rank-related anxiety. Participants can spend 0.50 EUR to reduce the number of correct lines of a randomly selected top-performing participant in their session, which may improve their relative rank. The outcome is a binary variable equal to one if the participant chooses to reduce another participant’s performance.
- Generalized trust. Participants allocate a fixed number of points between different in-group members (e.g., family, friends, or individuals sharing similar characteristics) and a random stranger from their country. The outcome is a continuous measure capturing the allocation to the stranger relative to in-group members, with higher values indicating greater generalized trust.

Experimental Design

Experimental Design
Participants are randomly assigned to one of three conditions: inequality of outcomes, inequality of opportunities, or a control condition with equal pay. In the inequality of outcomes condition, participants receive a randomly assigned bonus of 2 EUR or 8 EUR. In the inequality of opportunities condition, bonuses differ by gender. In the control condition, all participants receive the same bonus.
Participants then complete a competitiveness task, followed by a number of tasks designed to measure the proposed mechanisms: positional competition, rank-related anxiety, and trust. Finally, participants respond to a set of questions designed to measure moral universalism.
Experimental Design Details
Not available
Randomization Method
We will be using the built-in randomizer of Qualtrics, the survey software we are using for the experiment.
Randomization Unit
Observation unit, i.e. our unit of analysis: individual survey participants
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
The design is not clustered, it is implemented at the individual-level.
Sample size: planned number of observations
We plan to collect data of 360 participants (120 participants per condition). This pool consists primarily of undergraduate and graduate students who voluntarily register to participate in behavioral and economic experiments.
Sample size (or number of clusters) by treatment arms
360 participants, with 120 participants assigned to each condition: inequality of outcomes, inequality of opportunities, and equality.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
IRB

Institutional Review Boards (IRBs)

IRB Name
Ethical Review Committee Inner City Faculties, Maastricht University
IRB Approval Date
2026-03-04
IRB Approval Number
ERCIC_814_03_03_2026_Martorano
Analysis Plan

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