Why are some more peer than others? Evidence from a longitudinal study of social networks and individual academic performance
Highlights
► Analysis of peer effects in educational settings. ► Longitudinal data on academic performance, friendship, and advice relations among MBA students. ► Process of peer selection modelled by actor-oriented models. ► Social influence operates similarly for friendship and advice networks. ► High performers are less likely to initiating ties, to be chosen as friends but are sought after as advisors.
Introduction
Peer influence exists whenever individual behavior is affected by social interactions which are not constrained by pre-assigned roles and social positions (Leifer, 1988). As such the sociological relevance of peer influence is very general. Deviant behavior, opinion formation, generation of research ideas, and the emergence of status hierarchies are all examples of processes for which peer influence is likely to play a central role (Marsden and Friedkin, 1993; Mark et al., 2009; Rawlings and McFarland, 2011, Vásquez, 2010). In this paper we focus on educational settings where the effects of peer influence are viewed as consequences of interactions between students, and where the behavioral outcome of interest is the level of individual academic achievement (Burke and Sass, 2008, Frank et al., 2008, Winston and Zimmerman, 2003).
The existence and possible implications of peer effects in educational settings have been objects of cross-disciplinary debate at least since the influential “Coleman Report” which was among the first studies to suggest that individual academic attainment could depend on the average attainment of school peers (Coleman et al., 1966). Building on this early work, more recent research routinely considers the quality of academic peers at least as important an element of the social context as the quality of school resources (Jackson, 2009, Robertson and Symons, 2003). As a consequence of these developments, interest in models of peer influence has been steadily increasing (e.g., Hanushek et al., 2003, Sacerdote, 2001, Wentzel and Caldwell, 1997, Winston and Zimmerman, 2003). Despite extensive research, however, no agreement is yet in sight either about the existence and importance of peer influence, or about the most appropriate way to ascertain its behavioral consequences. Disagreement seems to be organized around two main empirical problems that, while widely acknowledged, remain unresolved.
The first problem is endogenous sorting arising from the fact that: “When individuals choose their peer groups, high ability students may sort themselves into peer groups with other high ability students. With ability only partially observable, positive estimates of peer effects may result even when no peer effects are present because of a positive correlation between the student’s unobserved ability and the observed ability of his peers” (Arcidiacono et al., 2009, p. 2). If peer group membership and individual attainment are simultaneously determined, then the level of individual attainment may be both an outcome of peer influence, as well as a basis for the formation of network ties between peers (Manski, 1993). Azoulay et al. (2009) consider this situation as an outcome of partially deliberate matching, or individual association decisions based on a limited number of contextually meaningful dimensions. By introducing in the classroom differentiation based on evaluation and ranking, the level of individual academic attainment affects which students are more likely to become “peers” (Tuma and Hallinan, 1979). When this happens, a dynamic feedback process links the possible consequences of social networks (social influence) to their antecedents (social selection). Thus it seems that models of peer effects not only have to identify the distinct contributions of social influence and social selection on individual behavior, but also have to account for the emergence of social organization (Coleman, 1988). In this study we develop a longitudinal approach to this problem based on assumptions that are directly testable given appropriate data. While analysis of longitudinal data is not unusual in sociological studies of peer effects in schools and other contexts (Duncan et al., 1968; Kandel, 1978), in this paper we go beyond existing work by emphasizing: (i) the local dependencies that social networks entail; (ii) how such dependencies change over time and across social relational settings, and (iii) the co-evolution of social structure and individual behavior.
The second problem concerns how, exactly, “peers” are selected, i.e., the role of agency in constructing the social conduits through which peer influence flows. Much of the economic literature on peer effects in education attempts to deal with the problem of endogenous sorting by experimental or quasi-experimental random assignment of students to peer groups (such as, for example, classmates or roommates) while ignoring the self-selection of friends and other peers representing both the sociologically relevant referents, as well as the subjectively meaningful sources of social influence (Imberman et al., 2009, Sacerdote, 2001, Zimmerman, 2003). Randomization alleviates endogeneity problems by treating peer selection as a research design issue, rather than as a sociological problem that requires modeling. Perhaps not surprisingly, the definition of peer groups by analytic convenience rather than sociological relevance often leads to a failure to find reliable evidence of peer effects (Foster, 2006). This study differs from prior attempts in that we define peers as those considered contextually relevant by the focal student (like, e.g., Lubbers et al., 2006). While this is not the first study of peer effects on academic achievement based on the direct observation of connectedness between students (Babcock, 2008), we are not aware of studies that have (i) analyzed data on complete networks of interaction between students; (ii) specified how patterns of local dependence entailed by these networks affect processes of social selection, and (iii) examined how peer effects may be both the outcome of, and the input to network ties.
We analyze data that we collected on individual academic attainment and interpersonal friendship and advice relations within a cohort of 75 students enrolled in a full-time Master in Business Administration (MBA) program. The cohort represents a complete intake of students and we followed it over the first 12 months of the program dedicated to coursework. Observations were recorded at three distinct occasions according to a panel design. Because educational institutions are both testing grounds for individual attainment as well as agents of socialization (Parsons, 1959), they represent ideal settings for examining how social structure and individual behavior affect one another and co-evolve. The data analysis is based on a family of stochastic models for network dynamics expressing social influence among peers, while at the same time incorporating a wide variety of mechanisms of social selection underlying the endogenous sorting of students into peer groups (Snijders et al., 2010, Steglich et al., 2010).
Section snippets
Peer effects under partially deliberate matching
Studies in the sociology and economics of schooling tend to agree that academic attainment is systematically affected by the interaction of school-based, personal, and social resources (Coleman et al., 1982, Hastings et al., 2006, Lazear, 2001, Sørensen, 1970). According to Coleman (1988, p. S104): “[A]n important form of social capital is the potential for information that inheres in social relations.” Identification of the effects of social capital on the basis of observed social relations
Representing and modeling change
According to Coleman (1988), social capital “[C]omes about through changes in the relations among persons that facilitate action [as] social capital exists in the relations among persons” (1988: S100–101. First emphasis added). How may this process of change be represented? Our strategy involves the specification of stochastic agent-based models expressing empirically observed changes in social relations and individual performance as time-aggregated outcomes of a series of individual decisions (
Setting
We followed a cohort of 75 students enrolled in a full-time residential MBA program offered by an elite Italian university. The program attracts students oriented toward managerial careers in private and public companies, consulting and service firms, and in the financial industry. Students come from a variety of backgrounds and are selected into the program on the basis of past academic success and professional achievement. The program requires full-time attendance and consists of a set of 28
Results
We start by presenting a qualitative interpretation of the estimates. Then we narrow the focus of the analysis and provide a post hoc numerical interpretation of the parameters of major theoretical interest. Table 5a reports the estimates of parameters in Eq. (1) specifying individual performance as a function of individual attributes and academic performance of network associates (or “peers”). Parameters are unstandardized, therefore the estimates for different parameters are not directly
Discussion and conclusions
A major line of contemporary sociological research builds on a theoretical framework which “[A]ccepts the principle of […] purposive action and attempts to show how that principle, in conjunction with particular social contexts, can account not only for the action of individuals […] but also for the development of social organization” (Coleman, 1988, p. S96). In this paper we have contributed to the refinement of this framework by providing a model linking the “action of individuals” to
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