This study examines the relationships between inter-firm relationship management variables and performance in industrial markets where a small number of buyers select from a large number of suppliers, in order to identify the characteristics of relationship management variables in the supply chain. To identify the attributes of relationship management variables, conflict factors were used as input variables in Data Envelopment Analysis (DEA) to classify firms into "efficient groups with low conflict with partner firms and high performance" and "inefficient groups with high conflict with partner firms and low performance," and the stratified effects of dependency, relational norms, relational commitment, trust, power, and contractual factors were examined. Furthermore, by classifying these characteristics into buyer firms and supplier firms, the study compared "the characteristics of relationship management variables of buyers and suppliers that manage conflict efficiently" with "the characteristics of relationship management variables of buyers and suppliers that manage conflict inefficiently," thereby re-examining the divergent findings presented in prior research on relationships in the supply chain. In a social context where there is considerable interest in the power dynamics between dominant and subordinate parties, the study examined whether the exercise of influence (power) by buyer firms that hold a power advantage over their counterparts is effective in terms of overall supply chain optimization—that is, in terms of performance for all members.