Trust Game

Background

The Trust Game is a classic socio-economic decision game to investigate interpersonal trust and reciprocity in an investment setting. It was originally introduced by Joyce Berg and colleagues in 1995 as the 'investment game' but the scientific community gradually changed its name to 'trust game' instead.

The Trust Game models situations in which two people must cooperate to increase their initial earnings, even though one person could take advantage of the other without consequences. The basic setup is as follows: two people play an 'investment' game and are randomly assigned to the role of playerA (makes the first decision) and playerB (makes the second decision). Both players get the same start capital ($10). PlayerA is asked to send some of their money to playerB ('invest') - the amount sent is always trippled by the game host. PlayerB must then decide how much money to return to playerA.

By sending some or all of the money, playerA has to trust that playerB will eventually return some money, otherwise playerA loses money and the investment made does not pay off. By returning some money, playerB has to reciprocate playerA's trust and share the gains (as they only got more money - the initial share plus the investment growth- because playerA trusted them).

Classic mathematical game theory predicts that people act selfishly and thus playerB should never share any of winnings. Likewise, anticipating this behavior, playerA should not share any money with playerB to begin with. Actual results challenge this view: people consistently trust and reciprocate with a win-win mentality, so that both players usually end up increasing their initial earnings.

The Millisecond Trust Game is not a true multi player game but simulates the behavior of coplayers with computer algorithms to pretend that participants play against real people. The default setting, assigns the 'true' participant roleA and plays only one game. Test administrators can easily change these settings and play more games (in which roles alternate), set the starting role of the participant and manipulate the reciprocity and trusting 'personality' of the computer confederate.

Task Procedure

Instructions tell participants that they will play a money game and explain the basic game rules. Participants are not informed that only one game will be played. The computer then pretends to find another player on the game network and assigns the participant 'roleA' ('trust'). The participant has then to decide how much of the initial start money ($10) to 'invest' by sharing it with playerB. An animation simulates the tripling of the money from participant to playerB. Once playerB receives the investment, it is up to playerB to decide how much of their money to share with playerA. Once the final share has been returned to playerA, the game ends (default setting).

What it Measures

The Trust Game is a measure of interpersonal trust and reciprocity

Psychological domains

• Social Norms: The unwritten, informal rules that define what is considered acceptable within a specific group
• Self-Interest: The drive to maximize one's own gains, even at the expense of others or regardless of social consequences
• Risk Assessment: Calculating the cognitive risk of betrayal versus the financial reward of cooperation
• Reciprocal Altruism: Evolutionary drive to help others with the expectation that the favor would be returned

Main Performance Metrics

• Proportion Invested: the proportion of the total earnings that are shared (and then tripled) with co-player; main measure of trust
• Proportion Returned: the proportion of the total earnings that are returned to co-player; main measure of reciprocity

Psychiatric Conditions

Research has identified significant behavior differences in the following groups when tested with the Trust Game:

• Borderline Personality Disorder (BPD)
• Schizophrenia
• Major Depression (MDD)
• Psychopathy
• Autism Spectrum Disorder (ASD)
• Frontotemporal Dementia

References

Search Google Scholar for peer-reviewed, published research using the Inquisit Trust Game.

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Berg, J., Dickhaut, J., & McCabe, K. (1995). Trust, reciprocity, and social history. Games and Economic Behavior, 10(1), 122–142.

Croson, Rachel, and Nancy Buchan. 1999. "Gender and Culture: International Experimental Evidence from Trust Games." American Economic Review, 89 (2): 386-391.

Chetty, Rinelle & Hofmeyr, Andre & Kincaid, Harold & Monroe, Brian, 2021. "The Trust Game Does Not (Only) Measure Trust: The Risk-Trust Confound Revisited," Journal of Behavioral and Experimental Economics (formerly The Journal of Socio-Economics), Elsevier, vol. 90(C).