Political Behavior, Vol. 22, No. 4, 2000 TRUSTING AND JOINING? An Empirical Test of the Reciprocal Nature of Social Capital Michele P. Claibourn and Paul S. Martin Thisarticletestsakeyhypothesisofthesocialcapitalliterature:voluntarymemberships and generalized trust reproduce one another. Panel data from the Michigan Socializa- tion Studies from 1965 to 1982 are used to test the contemporaneous and lagged effects of interpersonal trust on joining groups and the contemporaneous and lagged effects of joining groups on interpersonal trust. We find no evidence supporting the hypothesis that interpersonal trust encourages group memberships and only limited evidence suggesting that belonging to groups makes individuals more trusting. Key words: social capital; voluntary associations; interpersonal trust. INTRODUCTION In recent years both nonprofit foundations and government agencies have encouraged the proliferation of voluntary associations as a means of generating social capital, thought to provide resources that improve governance and gov- ernment accountability to citizens (Brehm and Rahn, 1997; Putnam, 1995, 2000). Despite the growing push to build social capital as public policy, and the ever-growing literature, there is still much uncertainty about the mecha- nisms that foster social capital and the effects of social capital on democracies. This article focuses on further understanding the mechanisms that reproduce social capital, specifically, the extent to which voluntary associations produce interpersonal trust, a form of social capital, and vice versa. Social capital originated as an ethically neutral resource produced as a by- product of social relationships (Coleman, 1988). Social capital as a resource available to individuals can take multiple forms, including norms, information, Michele P. Claibourn, University of Wisconsin at Madison; Paul S. Martin, University of Okla- homa, Department of Political Science, 455 W. Lindsey, Room 205, Norman, Oklahoma 73019 (psmartin@ou.edu). 267 0190-9320/00/1200-0267$18.00/0  2000 Plenum Publishing Corporation