It has to do with a group dynamic called "confidence matching," says a new study, and it's something to be aware of when you're facing tough choices.

By Amanda MacMillan
Updated June 02, 2017
Credit: Jacob Ammentorp Lund/Getty Images

Making group decisions among family, friends, or coworkers can be tough—especially when people have differing opinions, and some are more forceful about them than others.

Now, a new study in Nature Human Behavior reveals a common trap we tend to fall into with these situations: People often match their levels of confidence to the confidence levels of other people around them, even if those others have more—or less—expertise on the topic at hand.

The study serves as a reminder that just because people seem sure of themselves, it doesn’t necessarily mean they’re right. It also shows that, for better decision-making, it’s important for all of us to communicate our own level of certainty accurately, and not get swept up in “infectious” group dynamics.

To investigate decision-making behaviors in groups, researchers from Iran and the United Kingdom performed a series of six experiments involving 202 participants. In each experiment, people were asked—individually, in pairs, and in group settings—to determine which of two screens displayed a hard-to-see visual target, and to rate how sure they were of their choice.

The experiments were repeated several times, and participants received feedback about their accuracy and confidence levels. In the end, results showed that people adjusted their own confidence levels over time to match those of their fellow decision-makers. If they thought others’ confidence was higher, they tended to increase their own, and vice versa.

This works well when everyone in a group has similar experience and insight into a problem, the authors say. “Fortunately, that’s often the case,” they wrote in their paper, “as we tend to associate with friends, partners or colleagues with home we are likely to share traits.”

It can also be helpful when someone who really doesn’t know what they’re talking about nevertheless displays a lot of confidence; it can prompt others to speak up about their own opinions “in a way that better reflects their relative levels of expertise,” the authors wrote.

But when some people have more expertise than others, this confidence-matching behavior can also be harmful, they say. It “can cause miscommunication about who is more likely to be correct,” they wrote in their paper, and “is one reason why groups can fail to make good decisions.”

That was seen in the study, too. “We found that even when an expert is paired with someone who lacks expertise, both participants will align their confidence levels levels so that their opinions will carry more equal weight," said Dan Bang, PhD, a postdoctoral research associate at University College London, in a press release. (Some of the “partners” in the study were actually computer simulations, which allowed the researchers to manipulate their decision-making accuracy.)

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Bang says it can be difficult for people to express their opinions with the appropriate level of confidence relative to others in the group if they don’t know whether those people are modest or overly self-assured. People may also resort to confidence matching, whether consciously or subconsciously, as a way to avoid conflict or diffuse responsibility, he adds.

The researchers say their findings shed light on how confidence shapes public opinion, especially around hotly contested topics like climate change, politics, and the economy. The findings also highlight how groups make decisions on an everyday basis—and why, when you really do feel confident that you know what you're talking about, you might want to convince other people to follow your lead.