Psychological Review Copyright 1987 by the American Psychological Association, inc. 1987, Vol. 94, No. 3, 291-299 0033-295X/87/$00.75 Intergroup Competition for the Provision of Binary Public Goods Amnon Rapoport University of North Carolina--Chapel Hill Gary Bornstein Hebrew University of Jerusalem, Israel An experimental paradigm is proposed for investigating interpersonal conflicts under conditions of intergroup competition. The paradigm constitutes an n-person game with imperfect and incomplete information in which the n players arc divided into two groups, are each assigned monetary endow- ment, and must then decide independently and anonymously whether to keep the endowment or contribute it to the group's benefit. The group with the larger sum of contributions is provided with a monetary reward (binary public good), which is shared equally among all of its members regard- less of their decision. Two alternative models are proposed and their testable implications are de- rived and discussed. Both assume maximization of expected utility, but their assumptions about the expectations each player holds about the decisions of the remaining players are different. The ef- fects of predccisional communication arc examined and several extensions of the basic paradigm are outlined. Although the interest of social psychologists in intergroup re- lations has been growing rapidly (Billi~, 1976; Brewer, 1979; Tajfel, 1982), the experimental research in this area is still sparse, especially when compared with the vast amount of re- search on interpersonal relations (Rabbie, 1982). The difficulty of simulating complex intergroup relations in the laboratory is one reason for the field's slow development (Gerard & Miller, 1967; Rabbie, 1982). Another and perhaps more important reason appears to be the lack of an integrated theory. Thus, Rabbie (1982) wrote: Although the literature offers a number of hypotheses about inter- group relations, these hypotheses do not form an integrated theory. They are usually stated at one particular level of analysis, they are sometimes contradictory, and their supporting evidence varies widely. (p. 124) The development of an integrated theory has been especially hindered by the traditional distinction between the interper- sonal and intergroup levels of analysis. This distinction has characterized the theoretical study and experimental investiga- tion of social conflicts and competitions for many years (Tajfel, 1982). Despite recent attempts to simultaneously investigate the interpersonal and intergroup aspects of social conflicts in small groups (Brewer & Kramcr, 1986; Kramer & Brewer, 1984), the literature shows little success in closing the gap be- tween these two largely hypothetical levels of analysis. One possible way to narrow the gap is by designing and con- ducting systematic and theory-driven research of social situa- tions involving small groups, in which social conflicts occur si- multaneously at both levels of analysis. Extending the paradigm Preparation of this article was supported by grants from the Israel Foundation Trustees and the Faculty of Social Sciences at the Hebrew University of Jerusalem. Correspondence concerning this article should be addressed to Am- non Rapoport, Department of Psychology, University of North Caro- lina, Davie Hall 013A, Chapel Hill, North Carolina 27514. studied by van de Kragt, Orbell, and Dawes (1983) and building on the expected utility models proposed by Rapoport (1985, 1987) for this paradigm and its various modifications, the major purpose of our study is to propose an experimental paradigm and a psychological theory for interpersonal conflicts in small groups under conditions of intergroup competition. Specifi- cally, we will address the problem of interpersonal interaction in situations of intergroup conflicts concerning the provision of binary (step-level) public goods. The next four sections (a) discuss the problem of public good provision in intergroup con- flicts; (b) relate it to the problem of binary good provision in interpersonal settings; (c) present an experimental paradigm for studying the variables that affect the decision to contribute or not; and (d) propose two variants of an expected utility model that relate such decisions to the payoff structure, group size, and expectations each member of the two competing groups has about the decisions of the other members. In subsequent sections we investigate the effects of predecisional communica- tion on the individual decisions to contribute or not and discuss various testable implications of the models. Intergroup Competition as Public Goods Problems Intergroup conflicts are often centered on the acquisition of scarce resources (e.g., grazing land, monetary prizes) for which the groups compete. However, group competition may also oc- cur when the scarce resources have no value outside the context of the competition itself. This is the case when groups compete to achieve higher rank, enhance their prestige, or win a contest, examples of"social competition" as Turner (1975) has named it. Moreover, the study of minimal groups suggests that even when there is no explicit or institutionalized competition, groups tend to compete over positive social identity (Tajfel, 1982). Regardless of whether the scarce resources for which the groups compete are material or social and whether the ensuing conflict is designated as objective or social competition (Tajfel, 1982), the benefits associated with winning the competition are 291