By Matthew Warren

Political partisanship can be a major driving force behind many thoughts and behaviours, affecting obvious things like who to vote for, but also more tangential outcomes, such as how you interpret scientific evidence (liberals and conservatives alike tend to see evidence as more credible when it supports their ideological viewpoint).

But the situation is more complicated than that, as people’s actions are not always consistent with their political identity. What determines why about 8 per cent of Republicans voted for Hillary Clinton in the 2016 US presidential election, for example, rather than Donald Trump?

According to a paper published recently in Cognition, the answer may lie in how central an individual’s political affiliation is in the tangled web of features that make up their self-concept. A person’s identity contains a range of features, from characteristics like gender and age to political beliefs and moral principles. One feature can be caused by another: for example, someone might believe that they are an honest person as a direct result of the fact that they are also Christian. Previous research has suggested that the more “causally central” a feature is – that is, the more of these kinds of links that it has – the more fundamental it is to a person’s identity.

Stephanie Chen at London Business School and Oleg Urminsky at the University of Chicago wondered whether a person may be more likely to act in ways consistent with their political beliefs if they see their political identity as “causally central” to their self-concept, and they investigated this in an American and then a British context.

The pair first gave 243 American participants an online survey designed to measure aspects of their self-identity on the day before the 2016 presidential elections, including questions about their demographics and their political views, such as which political party they were affiliated with and their position on various issues like gun control and taxes.

The participants then answered a series of questions about how these various features of their identity related to each other – for example whether “being a Republican” or “being male” had an influence on other aspects of their personal identity. They repeated this process for each of the 20 features, providing a complete map of which bits of self-identity they felt were causally related. Finally, the day after the election, participants were asked which candidate they voted for, and how much they approved of the candidate their party had nominated.

Unsurprisingly, 89 per cent of Democrats and 71 per cent of Republicans voted for Hillary Clinton and Donald Trump, respectively. But the association between political affiliation and voting behaviour was not uniform: participants were more likely to have voted for their own party’s candidate if they saw their politics as more causally central to their self-concept.

Interestingly, this association held even when the researchers took into account how satisfied participants were with their own party’s candidate. “This result suggests that even among people who disapproved of their party’s candidate, those for whom political party was more causally central [in their self-concept] were more likely to nevertheless vote with their party”, write the researchers.

And this principle is not just limited to party affiliation – or unique to the United States. In a second study, 243 UK participants who identified as British or English completed a similar survey. But rather than looking at party affiliation, the researchers were interested in the centrality of national identity to people’s self-concept and how this related to their voting behaviour – this time in the Brexit referendum.

The authors found that people whose national identity (either their Britishness or Englishness) was central to their self-concept were more likely to have voted for Brexit.

The research sheds light on how political identity affects some people’s behaviour more than others, say the authors. But this research focused on outcomes directly relevant to a person’s political affiliations. It remains to be seen whether the “centrality” of people’s political beliefs in their identity also influences more downstream cognitive processes, such as how objectively they can appraise evidence that supports their political viewpoints.

—The role of causal beliefs in political identity and voting

Image: Protestor ‘Million Dollar Lex’ attends pro Brexit rally in Parliament Square on March 29, 2019 in London, England, the day that the UK was due to leave the EU. (Photo by Leon Neal/Getty Images)

Matthew Warren (@MattbWarren) is Staff Writer at BPS Research Digest