Compare methods

	Trust Game	Minimal Group Paradigm
Field	Social Psychology	Social Psychology
Family	Process / pipeline	Process / pipeline
Year of origin	1995	1971
Originator	Joyce Berg, John Dickhaut & Kevin McCabe	Henri Tajfel and colleagues
Type	Behavioral economic game as a social-psychology paradigm	Experimental paradigm for intergroup discrimination
Seminal source	Berg, J., Dickhaut, J., & McCabe, K. (1995). Trust, Reciprocity, and Social History. Games and Economic Behavior, 10(1), 122-142.	Tajfel, H., Billig, M. G., Bundy, R. P., & Flament, C. (1971). Social categorization and intergroup behaviour. European Journal of Social Psychology, 1(2), 149-178.
Aliases	Investment Game, Berg Game, Two-Player Trust Game	Minimal Group Experiment, Tajfel Matrices, Mere Categorization Paradigm
Related	3	3
Summary	The trust game, introduced by Berg, Dickhaut, and McCabe in 1995 (and often called the investment game), is a two-player exchange that operationalizes interpersonal trust and reciprocity in money. An investor receives an endowment and may send any portion to an anonymous trustee; the experimenter multiplies the transfer (typically tripling it); the trustee then decides how much, if any, to return. Standard game theory with purely self-interested players predicts the investor should send nothing because a selfish trustee returns nothing -- yet investors reliably send substantial amounts and trustees reliably return some, contradicting the narrow self-interest prediction. Because the amount sent cleanly measures trust and the amount returned measures trustworthiness, the paradigm became a workhorse in social psychology, behavioral economics, and neuroscience for studying social preferences and cooperation between strangers.	The minimal group paradigm is an experimental procedure, introduced by Henri Tajfel and colleagues in 1971, that strips intergroup conflict down to its barest possible cause: mere categorization. Participants are sorted into two groups on a trivial or random basis (for example, an alleged preference for one painter over another, or a coin toss), never meet other members, gain nothing personally, and then allocate points between anonymous in-group and out-group members using structured reward matrices. The striking and repeatedly replicated finding is that people favor their own group even when the category is meaningless and favoritism brings them no material gain. The paradigm became the empirical cornerstone of social identity theory, demonstrating that the cognitive act of dividing the social world into 'us' and 'them' is itself sufficient to produce discrimination.