ZUROFF ET AL. INVOLUNTARY DEFEAT STRATEGY DEPRESSION, PERCEIVED INFERIORITY, AND INTERPERSONAL BEHAVIOR: EVIDENCE FOR THE INVOLUNTARY DEFEAT STRATEGY DAVID C. ZUROFF McGill University MARC A. FOURNIER University of Toronto, Scarborough D. S. MOSKOWITZ McGill University The social competition theory (Gilbert, 2000; Sloman, 2000) attributes depression to activation of the Involuntary Defeat Strategy (IDS), which is postulated to have evolved to forestall defeated individuals from engaging in potentially dangerous contests with superior rivals. We sought to test this theory using an event–contin- gent recording method. One hundred and thirteen employed adults completed re- cords describing their social interactions over 20 days; the records assessed perceived inferiority to the other, perceived partner dominance, perceived partner Journal of Social and Clinical Psychology, Vol. 26, No. 7, 2007, pp. 751–778 751 David C. Zuroff, Department of Psychology, McGill University, Montreal, Quebec, Canada; Marc A. Fournier, Department of Psychology, University of Toronto, Scarborough, Ontario, Canada; D. S. Moskowitz, Department of Psychology, McGill Uni- versity, Montreal, Quebec, Canada. This research was supported by grants from the Social Sciences and Humanities Re- search Council of Canada, Les Fonds pour la Formation de Chercheurs et l’Aide à la Re- cherche du Québec, and Les Fonds Québécois de la Recherche sur la Société et la Culture to the first and third authors. We express our appreciation to Ella Vanderbilt and Elizabeth Foley for their help in col- lecting the data. We also thank Allison Kelly for her careful and thoughtful reading of a preliminary version of the article. We are especially grateful to Paul Gilbert, who has been exceptionally generous in help- ing us to understand evolutionary theory and in particular the relationships between so- cial rank and depression. He also made a great many suggestions that improved the quality of this article. Correspondence can be addressed to David Zuroff at david.zuroff@mcgill.ca.