In-group bias
Also known as: In-group favoritism
We favor, trust, and reward people we count as part of our group.
What it means
In-group bias is the tendency to evaluate, trust, cooperate with, and allocate resources to members of one's own group more favorably than to outsiders. Strikingly, Tajfel's minimal-group experiments showed it emerges even when group membership is assigned on a trivial, arbitrary basis with no history, contact, or material stake — merely being labeled as 'us' versus 'them' is enough to skew behavior. Social Identity Theory explains the mechanism: people derive part of their self-concept from group memberships and are motivated to see their groups (and therefore themselves) positively, so favoring the in-group becomes a route to self-esteem. An important nuance is that in-group favoritism and out-group hostility are dissociable — much discrimination operates by helping one's own group rather than actively harming others — and the strength of the bias varies with how central the identity is and how much groups compete. It matters because it is a root of prejudice, nepotism, in-group lending and hiring, political tribalism, and team rivalry, while also, more benignly, underpinning loyalty, solidarity, and cooperation within groups.
Examples
In minimal-group studies, people allocate more money to anonymous strangers merely assigned to their own meaningless 'group' than to those in the other.
A hiring manager lifts one CV to the top of the pile because the candidate went to her old university. She harms nobody; she just quietly helps one of her own.
In a well-known field study, football fans helped a stranger who stumbled far more readily when he wore their own club's shirt than a rival's. The shirt was the only difference.
First described in Henri Tajfel (1971); Social Identity Theory.