最小限のグループ パラダイムを作成します。

The minimal group paradigm is a method where researchers randomly assign participants to novel groups based on arbitrary criteria, stripping away confounds like monetary self-interest and historical conflict. This allows psychologists to isolate how social categorization alone influences intergroup behavior, revealing whether discrimination emerges purely from identifying with a group and separating the social world into 'us' versus 'them.'

Participants estimate the number of dots displayed on a screen across multiple trials. Their performance is then used to arbitrarily divide them into groups: in the neutral condition, they're labeled as under- or over-estimators based on their lowest or highest estimates; in the value condition, they're told their estimates were more or less accurate than average. This arbitrary classification establishes group membership without real differences.

Matrices present numbered choices in rows and columns, each supporting either in-group or out-group members. Participants select options that reward or punish group members. Scores range from 1 (minimum points for in-group) to 14 (maximum points), with 7.5 representing maximal fairness. Researchers analyze whether participants favor their in-group by choosing higher-scoring options when making differential choices between groups.

Results consistently show that despite arbitrary group assignments, participants demonstrate in-group favoritism when making differential choices between groups—significantly favoring their in-group members over out-group members. However, participants chose fairly when decisions involved only in-group or only out-group members, indicating that discriminatory behavior emerges specifically from intergroup comparisons rather than general unfairness.

Researchers have applied minimal groups to study empathy, finding that participants feel more empathy for in-group members in pain than out-group members. Using fMRI neuroimaging, studies show that activity in the orbitofrontal cortex mediates these biases. Notably, minimal group inductions can override racial categorizations, demonstrating that arbitrary social categorization powerfully shapes both emotional responses and neural processing of group members.

Researchers score each matrix choice from 1 to 14 and calculate average scores across choice types for each condition. One-sample t-tests determine whether individual mean scores significantly differ from 7.5, the point of fairness. This analysis reveals whether in-group favoritism in differential choices is statistically significant, confirming that discriminatory behavior emerges from social categorization rather than random variation.

The minimal group paradigm isolates the fundamental mechanisms of intergroup discrimination by removing real-world confounds. By demonstrating that arbitrary categorization alone produces in-group favoritism and discriminatory behavior, it reveals that prejudice and discrimination stem from basic social categorization processes rather than competition, conflict history, or stereotypes. This foundational insight has shaped decades of social psychology research on intergroup bias.