Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs. Compartments have been difficult to detect in empirical food webs because of incompatible approaches or insufficient methodological rigour. Here we show that a method for detecting compartments from the social networking science identified significant compartments in three of five complex, empirical food webs. Detection of compartments was influenced by food web resolution, such as interactions with weights. Because the method identifies compartmental boundaries in which interactions are concentrated, it is compatible with the definition of compartments. The method is rigorous because it maximizes an explicit function, identifies the number of non-overlapping compartments, assigns membership to compartments, and tests the statistical significance of the results. A graphical presentation reveals systemic relationships and taxa-specific positions as structured by compartments. From this graphic, we explore two scenarios of disturbance to develop a hypothesis for testing how compartmentalized interactions increase stability in food webs.

Regression coefficients cannot be interpreted as causal if the relationship can be attributed to an alternate mechanism. One may control for the alternate cause through an experiment (e.g., with random assignment to treatment and control) or by measuring a corresponding confounding variable and including it in the model. Unfortunately, there are some circumstances under which it is not possible to measure or control for the potentially confounding variable. Under these circumstances, it is helpful to assess the robustness of a statistical inference to the inclusion of a potentially confounding variable. In this article, an index is derived for quantifying the impact of a confounding variable on the inference of a regression coefficient. The index is developed for the bivariate case and then generalized to the multivariate case, and the distribution of the index is discussed. The index also is compared with existing indexes and procedures. An example is presented for the relationship between socioeconomic background and educational attainment, and a reference distribution for the index is obtained. The potential for the index to inform causal inferences is discussed, as are extensions.

Although the educational community has learned much about better educational practices, less is known about processes for implementing new practices. The standard model of diffusion suggests that people change perceptions about the value of an innovation through communication, and these perceptions then drive implementation. But implementation can be affected by more instrumental forces. In particular, members of a school share the common fate of the organization and affiliate with the common social system of the organization. Thus, they are more able to gain access to each others' expertise informally and are more likely to respond to social pressure to implement an innovation, regardless of their own perceptions of the value of the innovation. This article characterizes informal access to expertise and responses to social pressure as manifestations of social capital. Using longitudinal and network data in a study of the implementation of computer technology in six schools, the authors found that the effects of perceived social pressure and access to expertise through help and talk were at least as important as the effects of traditional constructs. By implication, change agents should attend to local social capital processes that are related to the implementation of educational innovations or reforms.

We contribute to debate about causal inferences in educational research in two ways. First, we quantify how much bias there must be in an estimate to invalidate an inference. Second, we utilize Rubin's causal model to interpret the bias necessary to invalidate an inference in terms of sample replacement. We apply our analysis to an inference of a positive effect of Open Court Curriculum on reading achievement from a randomized experiment, and an inference of a negative effect of kindergarten retention on reading achievement from an observational study. We consider details of our framework, and then discuss how our approach informs judgment of inference relative to study design. We conclude with implications for scientific discourse.

This study examines how high school boys' and girls' academic effort, in the form of math coursetaking, is influenced by members of their social contexts. The authors argue that adolescents' social contexts are defined, in part, by clusters of students (termed "local positions") who take courses that differentiate them from others. Using course transcript data from the recent Adolescent Health and Academic Achievement Study, the authors employ a new network algorithm to identify local positions in 78 high schools in the National Longitudinal Study of Adolescent Health. Incorporating the local positions into multilevel models of math coursetaking, the authors find that girls are highly responsive to the social norms in their local positions, which contributes to homogeneity within and heterogeneity between local positions.The adolescent is choosing how to invest time, and … the choices depend greatly on the social system surrounding them. (Coleman 1996, p. 346) This study examines how high school boys' and girls' academic effort, in the form of mathematics coursetaking, is influenced by their social contexts. The literature on sociology of education has established how adolescent coursetaking is influenced by schools' decisions and resource allocations (e.g., Natriello, Pallas, and Alexander 1989;Hallinan 1991;Useem 1992). Other sociologists have described education, independent of the school's function as a social institution, in terms of status attainment, arguing that adolescents and young adults are influenced by their parents' education, occupations, and aspirations (Sewell and Hauser 1976;Steelman and Powell 1991). Complementing status attainment theory, standard economic models directly address parents' motivations for investing in their children for long- (Adelman 1999). But, as implied by Coleman's quote in the epigraph above, while adolescents may be influenced by adults, including school faculty, administrators, and parents, they may also respond to their peers in making short-and longterm educational decisions (see also Sizer 1984;Crosnoe, Cavanagh, and Elder 2003; RiegleCrumb, Farkas, and Muller 2006). In this article we examine how an adolescent may be influenced in particular by the cluster of students with whom she takes courses-which we term the local position. NIH Public AccessWe focus specifically on effort in the domain of math coursetaking for four reasons. First, math has gained increasing attention in the popular press (e. Simpkins, Davis-Kean, and Eccles 2006) for its potential contributions to society. Second, math is an important gateway to other advanced courses and college entry and therefore to pursuing human capital (Sells 1973;Adelman 1999;Simpkins et al. 2006;Sadler and Tai 2007). Third, math has long been a key to the social organization of the school, as it is used to delineate academic tracks (Stevenson, Schiller, and Schneider 1994;Gamoran and Hannigan 2000;Lucas and Good 2001). Fourth, although math coursetaking has been the focus of considerable empirical study, ...