Having strong, biased opinions may say more about your own individual way of behaving in group situations than it does about your level of identification with the values or ideals of any particular group, new research suggests.

This behavioural trait – which researchers call 'groupiness' – could mean that individuals will consistently demonstrate 'groupy' behaviour across different kinds of social situations, with their thoughts and actions influenced by simply being in a group setting, whereas 'non-groupy' people aren't affected in the same way.

"It's not the political group that matters, it's whether an individual just generally seems to like being in a group," says economist and lead researcher Rachel Kranton from Duke University.

"Some people are 'groupy' – they join a political party, for example. And if you put those people in any arbitrary setting, they'll act in a more biased way than somebody who has the same political opinions, but doesn't join a political party."

In an experiment with 141 people, participants were surveyed on their political affiliations, which identified them as self-declared Democrats or Republicans, or as subjects who leaned more Democrat or Republican in terms of their political beliefs (called Independents, for the purposes of the study).

They also took part in a survey that asked them a number of seemingly neutral questions about their aesthetic preferences in relation to a series of artworks, choosing favourites among similar-looking paintings or different lines of poetry.

After these exercises, the participants took part in tests where they were placed in groups - either based around political affiliations (Democrats or Republicans), or more neutral categorisations reflecting their answers about which artworks they preferred. In a third test, the groups were random.

While in these groups, the participants ran through an income allocation exercise, in which they could choose to allocate various amounts of money to themselves, to fellow group members, or to members of the other group.

The researchers expected to find bias in terms of these income allocations based around political mindsets, with people giving themselves more money, along with people who shared their political persuasion. But they also found something else.

"We compare Democrats with D-Independents and find that party members do show more in-group bias; on average, their choices led to higher income for in-group participants," the authors explain in their study.

"Yet, these party-member participants also show more in-group bias in a second nonpolitical setting. Hence, identification with the group is not necessarily the driver of in-group bias, and the analysis reveals a set of subjects who consistently shows in-group bias, while another does not."

According to the data, there exists a subpopulation of 'groupy' people and a subpopulation of 'non-groupy' people – actions of the former type are influenced by being in group settings, in which case they are more likely to demonstrate bias against others outside their group.

By contrast, the latter type, non-groupy individuals, don't display this kind of tendency, and are more likely to act the same way, regardless of whether or not they're in a group setting. These non-groupy individuals also seem to make faster decisions than groupy people, the team found.

"We don't know if non-groupy people are faster generally," Kranton says.

"It could be they're making decisions faster because they're not paying attention to whether somebody is in their group or not each time they have to make a decision."

Of course, as illuminating as the discovery of this apparent trait is, we need a lot more research to be sure we've identified something discrete here.

After all, this is a pretty small study all told, and the researchers acknowledge the need to conduct the same kind of experiments with participants in several settings, to support the foundations of their groupiness concept, and to try to identify what it is that predisposes people to this kind of groupy or non-groupy mindset.

"There's some feature of a person that causes them to be sensitive to these group divisions and use them in their behaviour across at least two very different contexts," one of the team, Duke University psychologist Scott Huettel, explains.

"We didn't test every possible way in which people differentiate themselves; we can't show you that all group-minded identities behave this way. But this is a compelling first step."

The findings are reported in PNAS.