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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