An integrative social identity model of collective action (SIMCA) is developed that incorporates 3 socio-psychological perspectives on collective action. Three meta-analyses synthesized a total of 182 effects of perceived injustice, efficacy, and identity on collective action (corresponding to these sociopsychological perspectives). Results showed that, in isolation, all 3 predictors had medium-sized (and causal) effects. Moreover, results showed the importance of social identity in predicting collective action by supporting SIMCA's key predictions that (a) affective injustice and politicized identity produced stronger effects than those of non-affective injustice and non-politicized identity; (b) identity predicted collective action against both incidental and structural disadvantages, whereas injustice and efficacy predicted collective action against incidental disadvantages better than against structural disadvantages; (c) all 3 predictors had unique medium-sized effects on collective action when controlling for betweenpredictor covariance; and (d) identity bridged the injustice and efficacy explanations of collective action. Results also showed more support for SIMCA than for alternative models reflecting previous attempts at theoretical integration. The authors discuss key implications for theory, practice, future research, and further integration of social and psychological perspectives on collective action. Keywords: collective action, injustice, efficacy, social identityWhat is it that mobilizes people to participate in social protest? This has been a key question in social science from the foundation of its various disciplines, and numerous explanations have been explored. Research has examined social movements, social groups, and experimental groups, embedded in different social contexts, and studied with different methods and measures. Although qualitative reviews of this literature are abundant (e.g., Kelly & Breinlinger, 1996;Klandermans, 1997Klandermans, , 2004Marx & Wood, 1975;McPhail, 1971;Stürmer & Simon, 2004a), there is at present no quantitative research synthesis of the literature that focuses on multiple predictors of collective action and their interrelations. This is unfortunate for several reasons.First, although the literature on this topic is large and multifaceted there is substantial scope for theoretical integration (e.g., Klandermans, 1997Klandermans, , 2004. Indeed, given recent calls for greater integration in this domain, a quantitative synthesis that evaluates and integrates these theoretical advances would seem both timely and valuable. Second, a quantitative research synthesis of psychological predictors of collective action is of interest to disciplines including psychology, sociology, political science, and economics. In such a multidisciplinary arena, a key challenge is to bridge subjective (psychological) and social (structural) perspectives on when, why, and how people engage in social protest. This challenge is underlined by several recent efforts in the literature to a...

In 2 meta-analyses, we examined the relationship between perceived discrimination and psychological well-being and tested a number of moderators of that relationship. In Meta-Analysis 1 (328 independent effect sizes, N = 144,246), we examined correlational data measuring both perceived discrimination and psychological well-being (e.g., self-esteem, depression, anxiety, psychological distress, life satisfaction). Using a random-effects model, the mean weighted effect size was significantly negative, indicating harm (r = -.23). Effect sizes were larger for disadvantaged groups (r = -.24) compared to advantaged groups (r = -.10), larger for children compared to adults, larger for perceptions of personal discrimination compared to group discrimination, and weaker for racism and sexism compared to other stigmas. The negative relationship was significant across different operationalizations of well-being but was somewhat weaker for positive outcomes (e.g., self-esteem, positive affect) than for negative outcomes (e.g., depression, anxiety, negative affect). Importantly, the effect size was significantly negative even in longitudinal studies that controlled for prior levels of well-being (r = -.15). In Meta-Analysis 2 (54 independent effect sizes, N = 2,640), we examined experimental data from studies manipulating perceptions of discrimination and measuring well-being. We found that the effect of discrimination on well-being was significantly negative for studies that manipulated general perceptions of discrimination (d = -.25), but effects did not differ from 0 when attributions to discrimination for a specific negative event were compared to personal attributions (d = .06). Overall, results support the idea that the pervasiveness of perceived discrimination is fundamental to its harmful effects on psychological well-being.

The social environment comprising communities, families, neighbourhoods, work teams, and various other forms of social group is not simply an external feature of the world that provides a context for individual behaviour. Instead these groups impact on the psychology of individuals through their capacity to be internalised as part of a person's social identity. If groups provide individuals with a sense of meaning, purpose, and belonging (i.e. a positive sense of social identity) they tend to have positive psychological consequences. The impact of these identity processes on health and well-being is explored in the contributions to this special issue. In this editorial, we discuss these contributions in light of five central themes that have emerged from research to date. These themes address the relationship between social identity and (a) symptom appraisal and response, (b) health-related norms and behaviour, (c) social support, (d) coping, and (e) clinical outcomes. The special issue as a whole points to the capacity for a social identity approach to enrich academic understanding in these areas and to play a key role in shaping health-related policy and practice.

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This paper introduces a single-item social identification measure (SISI) that involves rating one's agreement with the statement 'I identify with my group (or category)' followed by a 7-point scale. Three studies provide evidence of the validity (convergent, divergent, and test-retest) of SISI with a broad range of social groups. Overall, the estimated reliability of SISI is good. To address the broader issue of single-item measure reliability, a meta-analysis of 16 widely used single-item measures is reported. The reliability of single-item scales ranges from low to reasonably high. Compared with this field, reliability of the SISI is high. In general, short measures struggle to achieve acceptable reliability because the constructs they assess are broad and heterogeneous. In the case of social identification, however, the construct appears to be sufficiently homogeneous to be adequately operationalized with a single item.

Two longitudinal studies considered the role of social identity factors in predicting well-being after students' transition to university. The transition (assessed before starting university and after 2 months at university) had a detrimental effect on well-being, but identification as a university student improved well-being. Both studies showed that the social context in which the change occurred either facilitated or hindered university identification. Specifically, perceived compatibility between old and new identities and having multiple group memberships (which were each influenced by social class background, Study 2) both increased likelihood of identification with the new group. These predictive relationships remained statistically reliable when controlling for other factors relevant to the transition. The results suggest that life transitions are difficult partly because they entail changes in group membership. Both studies also demonstrate that identification with a new group can help buffer individuals from the negative well-being consequences of change.

The authors examined the relation between perceptions of intergroup distinctiveness and intergroup differentiation in a meta-analysis. They tested the social identity theory prediction that low intergroup distinctiveness underlies differentiation (the "reactive distinctiveness" hypothesis) for effects on behavioral and judgmental differentiation. In addition, they examined the moderating power of 4 variables that H. Tajfel and J. C. Turner (1979) predicted would influence differentiation (group identification, relevance of the dimension of comparison, relevance of the outgroup. and nature of intergroup relations). Analysis of 60 tests revealed that the overall effect of distinctiveness on differentiation was not significantly different from 0, but reactive distinctiveness was found on behavioral differentiation measures, whereas reflective distinctiveness was found on judgmental differentiation measures. Only group identification was a reliable moderator. High identifiers showed reactive distinctiveness, whereas low identifiers showed reflective distinctiveness.

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