Similar results have been found in many other arenas. More than 90 percent of faculty members at one state university considered themselves above-average teachers. More than 30 percent of one company’s engineers rated themselves among the top 5 percent.

Studies like these led social scientists to conclude that people systematically exaggerate their own capabilities, that they have what researchers call “illusory superiority.”

But that’s not the whole story.

More recent studies have found examples in which people tend to underestimate their capabilities. One found that most people thought they would be worse than average at recovering from the death of a loved one . Another study reported that people thought they were worse than most at riding a unicycle. Here, they exhibit illusory inferiority.

So when are people likely to be overconfident in how they rank? And when are they underconfident?

One of us has conducted research on this topic. Spencer and his collaborators used Positly, a new platform he started that allows researchers to conduct a large number of studies rapidly. Instead of asking people where they rank on just a few skills, they asked where they ranked on 100 skills.

For each skill, participants were asked how they thought they compared with others on the platform who shared their age and gender, and lived in their area. If, on average, people thought they could outperform more than 50 percent of others at the task, that suggests systematic overconfidence. If, however, people thought they would outperform less than 50 percent, that’s evidence of underconfidence.