Developmental Psychology 1999, Vol. 35, No. 5, 1179-1188 Copyright 1999 by the American Psychological Association, Inc. 0012-1649/99/S3.00 It Takes Two to Fight: A Test of Relational Factors and a Method for Assessing Aggressive Dyads John D. Coie Duke University Antonius H. N. Cillessen University of Connecticut Kenneth A. Dodge Vanderbilt University Julie A. Hubbard University of Delaware David Schwartz University of Southern California Elizabeth A. Lemerise Western Kentucky University Helen Bateman Vanderbilt University Observations of aggressive interactions in boys' laboratory play groups were used to evaluate the relative importance of relational and individual factors in accounting for aggressive acts. A classroom peer-rating method for identifying mutually aggressive dyads was validated in 11 5-session play groups, composed of 2 mutually aggressive boys and 4 randomly selected male classmates from 11 predominately African American 3rd-grade classrooms. When the social relations model was used, relationship effects ac- counted for equally as much of the variance in total aggression and proactive aggression as either actor or target effects. Mutually aggressive dyads displayed twice as much total aggression as randomly selected dyads. Members of mutually aggressive dyads attributed greater hostile intentions toward each other than did randomly selected dyads, which may serve to explain their greater aggression toward each other. The importance of studying relational factors, including social histories and social-cognitive processes, is discussed. The study of human aggression has usually been dominated by a focus on individual aggressiveness, without adequate recognition of the significance of interpersonal relationships in the occurrence of aggression. This may in part be due to the exceptional stability and cross-situational consistency of individual aggressiveness. The estimates of stability calculated in Olweus's (1978) review of this literature are as high as for any other individual characteristic (r = .76 for 1-year and .60 for 10-year intervals). Huesmann, Eron, John D. Coie, Department of Psychology, Duke University; Antonius H. N. Cillessen, Department of Psychology, University of Connecticut; Kenneth A. Dodge, Department of Psychology and Human Development, Vanderbilt University; Julie A. Hubbard, Department of Psychology, Uni- versity of Delaware; David Schwartz, Department of Psychology, Univer- sity of Southern California; Elizabeth A. Lemerise, Department of Psy- chology, Western Kentucky University; Helen Bateman, Learning Technology Center, Vanderbilt University. Kenneth A. Dodge is now at the Sanford Institute of Public Policy, Duke University. This research was supported by National Institute of Mental Health (NIMH) Grant R01 38765 and NIMH Research Scientist Awards K05 MH00797 and K05 MH 01027. We are grateful to David Kenny and Robert Terry for statistical consultation. Correspondence concerning this article should be addressed to John D. Coie, Department of Psychology, Duke University, Box 90085, Durham, North Carolina 27708-0085. Lefkowitz, and Walder (1984) obtained a correlation of .58 for peer-rated aggression from Ages 8 to 30. Cairns and Cairns (1994) have reported comparable stability in aggressiveness for males and females. Likewise, there is now a reasonably coherent develop- mental account of the factors contributing to chronic aggressive- ness across childhood and adolescence (e.g., Coie & Dodge, 1998; Patterson, 1993; Patterson, Reid, & Dishion, 1992). Nonetheless, despite the importance of individual factors in the prevalence of violence and aggression in human interactions, there is reason to consider the role of relational or dyadic factors in the occurrence of aggression among individuals. Most of the homi- cides in the United States, for example, occur during arguments between relatives or acquaintances (Kellerman & Reay, 1986). One possible explanation for this fact is that acquaintances and relatives interact more frequently than strangers and thus have greater opportunity for misunderstandings and conflicts that would lead to aggressive acts. Closely related to this explanation is a second one—namely, that this greater frequency of social interac- tion can lead to expectations between individuals that serve to lower the threshold of incentive for aggressive actions by one person toward the other. For example, two individuals who have had a history of misunderstandings might be more apt to draw hostile inferences about the intentions of the other in some situa- tions than they would in similar situations with a total stranger or with another acquaintance. 1179 This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.