Prevalence-Induced Concept Change in Human Judgment

Abstract

Why do social problems seem so intractable? In a series of experiments, I show that people often respond to decreases in the prevalence of a stimulus by “expanding their concept” of it. When blue dots became rare, participants began to see purple dots as blue; when threatening faces became rare, participants began to see neutral faces as threatening; and when unethical requests became rare, participants began to see innocuous requests as unethical. This prevalence-induced concept change occurred even when participants were forewarned about it and even when they were instructed and paid to resist it. I then present a computational model suggesting that this phenomenon is driven by a range-frequency compromise in judgment. One reason social problems may seem so intractable is that a reduction in their prevalence can lead people to see more of them.