North Wales Clinical Psychology Programme, School of Psychology, Bangor University, Wales, United Kingdom.
Soc Sci Med. 2020 Aug;258:113016. doi: 10.1016/j.socscimed.2020.113016. Epub 2020 May 29.
The group density effect, where a group member's psychiatric risk is associated with the proportion of the local population their group comprises, demonstrates the importance of minority group status to mental health. Previous research, focusing on ethnicity, has been correlational, but newly-formed identities provide opportunities for natural experiments, with greater scope for causal inference. This study examines whether such a group density effect can be found for the novel Brexit identities of 'leaver' and 'remainer' following the UK's divisive 2016 referendum on EU membership. Mixed effects models were fitted to the Understanding Society panel survey series (N = 25,555, 19,767 for analyses controlling for pre-referendum mental health data), predicting mental health as a function of individual opinion on EU membership and local referendum results. These interacted such that those holding the local majority opinion had better mental health (Odds ratio (OR):875 [0.766- 0.9995]), compared to those in the minority. This result survived adjustment for individual and area-level economic circumstances (OR:866 [0.758-0.989]), and, strikingly, pre-referendum mental health (OR: 0.841 [0.709-0.998]), as well as a number of other potential confounding variables. The results provide evidence for rapidly forming group density effects based on de novo identities, and suggest that identity may be a causal mechanism for group density effects more broadly. They also speak to the extent of polarisation in the Brexit-era UK, and its public health consequences.
群体密度效应表明，群体成员的精神健康风险与他们所在群体在当地人口中的比例有关，这凸显了少数群体地位对精神健康的重要性。之前的研究主要关注种族，但新形成的身份为自然实验提供了机会，从而更有可能进行因果推断。本研究考察了在英国 2016 年关于欧盟成员资格的分裂公投后，是否可以找到“脱欧派”和“留欧派”这两个新的英国脱欧身份的群体密度效应。使用混合效应模型对“理解社会”小组调查系列（N=25555，分析中控制了公投前的心理健康数据，有 19767 人）进行了拟合，根据个人对欧盟成员资格的看法和当地公投结果预测心理健康状况。这些结果相互作用，使得那些持有当地多数派观点的人心理健康状况更好（优势比（OR）：875[0.766-0.9995]），而那些持少数派观点的人则不然。这一结果在调整了个人和地区经济环境（OR：866[0.758-0.989]）以及令人惊讶的是，在公投前的心理健康状况（OR：0.841[0.709-0.998]）后仍然成立，以及其他一些潜在的混杂变量。这些结果为基于新形成的身份的快速形成的群体密度效应提供了证据，并表明身份可能是更广泛的群体密度效应的一个因果机制。它们还反映了英国脱欧时代的两极化程度及其对公共卫生的影响。
