Psychol. Sci. http://doi.org/cbsb

The role that institutional decisions play in effecting social change is a question with a long history, but evidence that such decisions play a role in shifting personal attitudes is mixed. Attitudes, however, are not the only determinants of behaviour. Perceptions of social norms — what most others in a group believe or do — are also consequential.

In new research, Tankard and Paluck asked whether perceptions of social norms and personal attitudes changed as a result of the June 2015 US Supreme Court ruling in favour of same-sex marriage. In an experiment carried out before the ruling and a five-wave longitudinal time-series study in the few months before and after the ruling, Tankard and Paluck found that perceived norms shifted towards increased support for gay marriage and gay people in response to the actual ruling (time-series study) or a hypothetical favourable ruling (experiment). Although a positive effect on attitudes was only obtained in the experiment, the shift in perceived norms was robust across the two data sets, as well as a third replication data set.

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The study provides evidence for a substantial effect of a landmark US Supreme Court ruling on public perceptions of support for gay marriage. A crucial outstanding question is how this shift in perceived norms might ultimately affect individual and collective behaviours.