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.

In the present research, we introduced a conceptual framework of inclusion and subsequently used this as a starting point to develop and validate a scale to measure perceptions of inclusion. Departing from existing work on inclusion and complementing this with theoretical insights from optimal distinctiveness theory and self‐determination theory, we proposed that inclusion is a hierarchical two‐dimensional concept consisting of perceptions of belonging and authenticity. In addition, we posed that in the process of inclusion, it is the group rather than the individual that has primary agency. From this conceptualization, we developed and validated the 16‐item perceived group inclusion scale (PGIS). Data from two samples supported our proposed configuration of inclusion. In addition, the PGIS appeared to be a reliable measure of inclusion and was demonstrated to possess both nomological and predictive validity. Taken together, this research contributes to the conceptual refinement of the inclusion construct and offers researchers a reliable and valid tool to conduct future inclusion research. Copyright © 2014 John Wiley & Sons, Ltd.

This article examines inductive processes of social identity formation, the bottom-up processes by which individual group members influence a social identity, integrating it with work on entitativity. Three studies tested the prediction that feelings of individual distinctiveness mediate the relation between inductive social identity formation and entitativity and that entitativity in turn predicts identification. The studies provided consistent support for this theoretical model over alternative models, using a range of different social groups and methods. Study 1 found support for the model in self-selected small groups. Study 2 supported it with a much broader set of groups that were not self-selected. Finally, Study 3 varied levels of inductive social identity formation systematically by varying group size and provided direct support for the hypothesized causal relations.

Research on in-group identification typically focuses on differences in individuals' identification at the individual level of analysis. We take a multilevel approach, examining the emergence of group influence on identification in newly formed groups. In three studies, multilevel confirmatory factor analysis confirmed two dimensions of identification-self-definition and self-investment (Leach et al., 2008)-at both the individual and the group level. As expected, the group had greater influence on individuals' identification the more group members interacted with each other. This was shown in experiments with varying amounts of real interaction (Study 1), in a longitudinal study of student project groups (Study 2), and in a longitudinal study that experimentally mimicked the development of online communities (Study 3). Together, these studies support a developmental model of identification at the group level that has implications for the understanding of social identity and small-group dynamics.

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