Reciprocity-Norm Similarity and Cooperative Investment Within Friendships

Abstract

Cooperation among non-kin is sustained through repeated interactions and expectations of future reciprocity. The present study examined whether perceived similarity in reciprocity norms was associated with helping within established friendships and whether this association varied with helping cost. Participants were 255 Japanese adults who identified a same-gender friend living nearby and rated their perceived similarity to that friend in reciprocity norms, other moral concerns, physical appearance, tastes, and values. They also reported past low- and medium-cost help provided to and received from the friend and anticipated helping in hypothetical high-cost situations. Primary analyses controlling for relationship characteristics indicated that reciprocity-norm similarity was significantly associated with the provision of low-cost help (emotional support), but not with medium- or high-cost helping or help received. Exploratory FDR-adjusted analyses indicated that similarities in physical appearance and tastes were associated with helping in some higher-cost contexts. These findings suggest that perceived similarity in reciprocity norms may signal compatibility in cooperative decision rules and guide low-cost cooperative investment within established friendships.