Why do some people vote for candidates who aren’t in their best interest? According to researchers from Duke University, it may come down to a voter’s self-image.

The researchers propose that there are two motivations -- policy positions and social identity -- which compete to shape which candidate someone will choose or whether they will vote at all.

Policy positions are a rational way to decide, where someone picks a president whose policies align more closely with their own. Social identity is what their vote means for their own self-image and how others see them.

The internal battle between the two could explain why some people vote for candidates who aren’t in their best interest.

"We think that treating identity as something that competes with policy helps explain why voters often select candidates whose policies go against their own interests," said co-author Scott Huettel, chair of psychology and neuroscience at Duke.

They suggest that there are three main ways identity could outweigh rational choice.

First is when the actual act of voting reinforces the voter’s self-identification, such as with other voters of that party.

"People are deciding to vote not because their vote has a material effect on their future, but because the act of voting signals something to themselves and others," Huettel said.

Huettel provides the example of the ‘Brexit’ vote.

"For many people, the vote to leave the European Union is a signal that you supported your country, you're patriotic, you're a nationalist," Huettel said. But a different identity could reinforce a vote to stay, such as in those people who identify as being a European or a citizen of the world.

Second is when someone votes because of peer pressure or to maintain their reputation.

And finally, when deciding to vote some people may place more value on the identity variables than the policy variables.