Votes are cast based on rational decisions, right? Not necessarily – we may not be as in control of our preferences as we like to think, writes Zaria Gorvett.

It hits the moment you board the train – that unmistakeable tang of stale urine. You take a seat. The passenger opposite sneezes across the aisle. As you move out of the way, your foot lands in a gooey clot of chewing gum. Disgusted yet? How you react may say more about you than you might realise – it may even reveal your political leanings.

It’s not the only thing that can influence your politics without your knowledge. Whenever an election looms, voters must spend months wrestling with policies, politicians, and ideologies. As voting day arrives, it’s time for some rational calculations at the ballot box. Or is it?

We may not be as in control of our own vote as we like to think, according to many psychologists. Education, healthcare, and the economy all matter, but voter choices can also be swayed by factors ranging from how easily disgusted and fearful people are, to how they react to the weather and sports results.

Subtle sway

It’s well known that our conscious decisions are routinely influenced by unconscious thought-processes, emotions and prejudices. Jon Krosnick, political science professor at Stanford University, has devoted his career to the phenomenon. “What we know now from 50 years of psychology is you can divide the brain into two parts,” he explains. “In fact, all decision-making is unconscious.”

Krosnick argues that during televised debates, although voters are listening to the candidates, other factors can have as much, if not more, impact on voters’ decisions. For example, he and colleagues found that in the 2008 US presidential election, many voters were more influenced by the ethnicity of the candidates – Barack Obama and John McCain – than they may have realised themselves. People with higher scores of implicit racial prejudice – which is unconsciously-held – were less likely to vote for Obama.

Yoel Inbar, a psychology professor at the University of Toronto, studies another hidden way we may be influenced – by things that trigger feelings of disgust. Inbar placed test participants on a ‘disgust scale’, asking them to rate their agreement with stomach-wrenching statements and situations, such as “you discover that a friend of yours changes underwear only once a week.” Subjects were then quizzed on their political ideology.

He found that the more easily disgusted tend to be politically conservative. “We have good data on basically every world region except sub-Saharan Africa. And we see a pretty consistent relationship”, Inbar says.

Inbar believes the political and moral associations with disgust and disease can be explained by some prehistoric biology. As people started to spend more time in large social groups, they developed a set of behaviours that would minimise the risk of catching disease, what psychologists call the ‘behavioural immune system’.

Other research suggests that how you feel on the day may have an influence too.  One study found that making people think about disease can encourage them to think negatively about racial differences. Similarly, a US study in 2014 found that people who felt unwell were more likely to favour attractive candidates than their less physically appealing opponents.

“The attitudes that flow from the behavioural immune system are things we tend to think of as socially conservative,” says Inbar. “They are about avoiding groups that you are not familiar with, about adhering to traditional social practices, and they are also about sexual restrictedness. Disgust is the emotion that really says ‘hey don’t do that, stay away from that, that’s dangerous for you’.”

Intriguingly, in another experiment, Inbar and colleagues found that priming people to feel disgust – using bad smells in a room – made them temporarily more likely to shun certain minority groups, such as homosexual men.

The implication is that political campaigning and media commentary using disgust triggers – for example, saying policies ‘stink’ – may have a deeper influence on some people than first appears. A few years ago, one US politician took this to an extreme by infusing campaign leaflets with the smell of garbage.

Strong fear

A study into the impact of 'fear sensitivity' on political ideology suggests similar conclusions. A group of 46 people from Nebraska were asked about their views on a range of political issues, from the Iraq war to capital punishment. Those with strong opinions were invited to continue to part two.

Next the volunteers were subjected to a series of threatening images, such as a frightened man with a spider on his face, and were startled with loud noises while they were assessed for physiological responses to fear, such as how conductive their skin was. The researchers found that the more easily startled people in the group tended to have more right-wing views, a result which fits with an emerging pattern of conservatives as more sensitive to negative aspects of the environment.

So perhaps political rhetoric that provokes fear – emphasising the risks of terrorism, economic instability and so on – can have a subtle but powerful effect on some groups of people when it is used to try and sway votes.

Go negative

Other subconscious biases are already exploited by political campaigns. One such effect is the so-called ‘negativity bias’, a well-documented tendency of people to preferentially remember negative information, and allow negative emotions to dominate decision-making.

Krosnick’s research suggests that when politicians emphasise the negative qualities of their opponent, it can increase turnout of their supporters. Back in the 1990s, he studied how people’s feelings towards politicians affected their likelihood of turning up to vote. As you would expect, he found that liking both candidates equally affords little motivation to vote. But even if a voter likes them unequally, they still aren’t very interested. Dislike, on the other hand, is a much more compelling reason to cast one’s ballot. “If you dislike at least one of the two candidates, then you really are motivated to participate – so in other words it’s really disliking a candidate that motivates turnout,” says Krosnick.

Decisions based on negative emotions can also work the other way. A growing body of evidence shows that voters unconsciously punish politicians when things don’t go their way – even issues entirely unconnected to politics.

Such fickle voting habits are most vividly illustrated in the contest between Al Gore and George W Bush in 2000. The election followed a series of severe droughts and floods, which left political scientists Larry Bartels and Christopher Achen wondering: would voters blame their bad luck on the incumbent Democrats? An analysis of voting and weather patterns across 54 states showed that their share was up to 3.6% lower than it normally would have been. Or as the authors put it "2.8 million people voted against Al Gore in 2000 because their states were too dry or too wet".

Such retributions are not unique to the weather – the effect stretches to football results, too. A US study of electoral outcomes over 44 years found that local college games up to 10 days before had an impact, with surprising results bestowing the most favour on incumbent politicians.

If voting patterns can come from unconscious biases, does that decrease their validity? “It’s an interesting question”, says Inbar. “[If] I can explain why you like ice cream, are you then wrong to like ice cream? On an individual basis, I don’t think so.”

Yet it’s clearly worth being aware of the factors that may trigger your hidden biases the next time you place your vote in the ballot box.

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What the candidates actually say has little impact on voters’ decisions