Collective Risk Social Dilemma and Equilibrium Reasoning

Last registered on June 23, 2026
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Pre-Trial

Trial Information

General Information

Title
Collective Risk Social Dilemma and Equilibrium Reasoning
RCT ID
AEARCTR-0018962
Initial registration date
June 22, 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
June 23, 2026, 8:50 AM EDT

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

Locations

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Primary Investigator

Name
Alice Bell
Affiliation
university of southampton
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Other Primary Investigator(s)

Additional Trial Information

Status
In development
Start date
2026-06-22
End date
2026-07-18
Keywords
Behavior, Environment & Energy, Governance
Additional Keywords
JEL code(s)
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
This study uses a lab experiment to examine whether failures of equilibrium reasoning affect support for carbon taxes in a Collective Risk Social Dilemma (CRSD) setting. Pairs of participants play a consumption-based CRSD game with a tipping point. Consumption produces a Byproduct, and exceeding the byproduct production threshold triggers a 70% probability of losing all tokens. The game is played in three variants: a baseline without tax, a game with tax that affects players equally, and a game with tax that creates inequality through redistribution.
The tax alters the game's equilibrium, making both the private and social equilibria superior. If a failure of contingent thinking (Niederle and Vespa, 2023) is present, participants may still vote against it if they fail to anticipate how opponents will adjust their behaviour under the new rules.
After experiencing both a taxed and untaxed game, participants vote for their preferred version to play in a final round, with their stated beliefs about opponent behaviour elicited after the vote. At this stage, some players undergo an intervention to correct the FCT.
The study aims to shed light on why carbon taxes may lack public support even when they improve outcomes, and whether inequality created by tax design compounds this effect.
External Link(s)

Registration Citation

Citation
Bell, Alice. 2026. "Collective Risk Social Dilemma and Equilibrium Reasoning ." AEA RCT Registry. June 23. https://doi.org/10.1257/rct.18962-1.0
Sponsors & Partners
Experimental Details

Interventions

Intervention(s)
Intervention Start Date
2026-06-22
Intervention End Date
2026-07-18

Primary Outcomes

Primary Outcomes (end points)
Presence of failure of contingent thinking (FCT), effect of FCT on vote choice, inequality effect on FCT, effect of the intervention on FCT, redistribution between players
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Payoff of the collective risk social dilemma (CRSD) game; success in avoiding the tipping point; assessment of opponents' behaviour; political, ecological, and risk preferences' effects on CRSD.
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
This experiment uses a variant of the Collective Risk Social Dilemma (CRSD) game, adapted for a consumption context following Bachler et al. (2024). Players make repeated contribution decisions over multiple rounds, facing the risk of a catastrophic loss if a threshold is exceeded. The experiment uses three variations of the game, differing in whether a tax is applied and whether that tax creates inequality between players. After experiencing multiple game variants, participants vote on which game they would like to play again. A randomly selected subset of participants receive an intervention during the voting stage designed to support reasoning about how their opponent is likely to behave. Participants then complete a questionnaire eliciting attitudes relevant to the experiment.
Experimental Design Details
Not available
Randomization Method
Treatment assignment to game variant (equal or unequal tax) is determined by systematic sequential assignment, cycling through conditions in order as participants arrive. FCT intervention assignment is determined independently for each individual by a computer-generated random draw with 50% probability.
Randomization Unit
There are two levels of randomisation. Game variant is assigned at the individual level on arrival, with participants subsequently paired within treatment by instruction completion time, making the pair the effective unit of analysis. The FCT intervention is assigned at the individual level independently, with each participant having an equal probability of assignment regardless of their partner's assignment.
Was the treatment clustered?
Yes

Experiment Characteristics

Sample size: planned number of clusters
104 pairs
Sample size: planned number of observations
208 individuals
Sample size (or number of clusters) by treatment arms
26 pairs, untaxed game followed by equal tax
26 pairs, untaxed game follwed by unequal tax
26 pairs, equal tax game follower by untaxed game
26 pairs unequal tax game followed by untaxed game

104 individuals with intervention to correct failure of contingent thinking,
104 without intervention
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials
IRB

Institutional Review Boards (IRBs)

IRB Name
University of Southampton Faculty of Social Sciences Ethics Committee
IRB Approval Date
2025-12-16
IRB Approval Number
108896
Analysis Plan

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