Collective protest movements are assumed to gain momentum when people see others joining. However, research on the impact of descriptive participation norms is scarce and has produced inconsistent results, partially because experimental manipulation of descriptive norms is difficult in real-world contexts. In two experiments (N = 235/330) we successfully manipulated descriptive norms of participating in protests of the Portuguese housing movement using a self-persuasion-technique. Participants were told that members of a relevant reference group (i.e., young people in Experiment 1 and Portuguese people in Experiment 2) participate more (vs. less) in the housing movement than other groups. After that participants were asked to explain why that is the case. Based on the Social Identity Model of Collective Action (SIMCA) we predicted that high-participation norms increase own intentions to engage in general, conventional (i.e., normative), non-normative and even violent collective protest actions, and that this effect should be mediated by the SIMCA factors of collective action, that is, increased politicized identification (i.e., with the movement), moralization, perceived injustice and collective efficacy. Results in both studies show the predicted positive indirect effect on all forms of collective protest when considering joint mediation by all four SIMCA factors. However, there was no total effect of descriptive norms on intentions to participate in the protests. Moreover, in Experiment 1 there was even a negative direct effect of high participation norms when the indirect effects via the SIMCA factors were controlled. These results speak for an ambivalent role of descriptive norms: When perceiving others participating in the movement, people may indeed be more inclined to participate due to increased politicized identification, moralization, perceived injustice and efficacy. However, they may also be affected by substitutability considerations (e.g., free-riding on others’ engagement) as has been found in some previous studies. Additionally, specific mediations (i.e., indirect effects via single SIMCA factors while statistically controlling the others) differed between studies. Norm effects were mediated by politicized identification with the movement’s activists in Experiment 1 and moralization of housing difficulties, in Experiment 2. These differential effects can be explained by distinct characteristics of the reference groups used for the norms manipulation, that is, young people versus Portuguese, respectively. Thus, while SIMCA-factors may generally predict collective action as claimed in SIMCA, their relative importance seems to be context dependent and vary across social identities. Interestingly, the result that injustice and efficacy were less important predictors of collective action than politicized identity and morality partially contradicts the more recent proposal of a dual-chamber version of SIMCA (Agostini & van Zomeren, 2021). It is also inconsistent with participants’ responses to the open question in the self-persuasion task, which often attributed high participation to injustice and low participation to lack of efficacy. We conclude that both participants’ reasoning and researchers’ intuitions may often be inaccurate when trying to capture people’s motivations for (non-)participation in collective action. Agostini, M. & van Zomeren, M. (2021) Toward a Comprehensive and Potentially Cross-Cultural Model of Why People Engage in Collective Action. Psychological Bulletin, 147(7), 667–700. DOI: 10.1037/bul0000256

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Collective action,SIMCA,Descriptive Norms