Conformity
Conformity is changing what you say or do to match a group, including when you can see the group is wrong. Solomon Asch's line-judgment studies are the founding demonstration: 123 American male students gave the wrong answer on 37 per cent of critical trials, 75 per cent went along at least once, and 5 per cent went along every time. The number that did not reach the textbooks is that roughly two thirds of responses were independent, and Asch himself read that as the more striking result.
What it is
The task was not ambiguous. Participants were shown a reference line and three comparison lines, and asked which of the three matched. Alone, people were right almost every time. In a room with confederates who confidently gave the wrong answer, they were not.
Asch ran the studies in 1951 and reported them at length in 1956. The headline figures are well known. One hundred and twenty-three American male students; wrong answers on 37 per cent of critical trials; 75 per cent of participants conforming at least once; 5 per cent conforming on every critical trial. The part that carries the meaning is the debrief. Many participants knew the correct answer perfectly well. They could see the lines. They said the wrong thing anyway, and reported doing it so as not to stand out, which makes the behaviour a transaction rather than a perceptual mistake. They were not fooled. They paid.
Then there is the number the discipline dropped. Roughly two thirds of responses across the studies were independent. Most people, most of the time, said what they saw. Asch had designed the studies expecting to demonstrate independence, and he read his own data as showing more of that than of conformity. What entered the textbooks was the inverse, taught as a lesson in how easily people fold. The finding did not change. The framing did, and the framing tells you what the discipline found interesting rather than what it found.
Both numbers describe the same event from opposite ends. A third of the time the group collected. Two thirds of the time it did not, and the person absorbed the cost of dissent instead. Reporting either half on its own produces a different claim about human beings, and the half that circulated is the pessimistic one.
The rate is also not fixed, which is the most practically useful thing anyone has established about it. Rod Bond and Peter Smith pooled 133 Asch-type line-judgment studies across 17 countries in 1996 in Psychological Bulletin, and found two moderators that matter. American conformity has declined since the 1950s, so Asch's figure describes a period as well as a species. And collectivist countries show more conformity than individualist ones, so it describes a place. A price that moves with time and culture is a price somebody is setting, which means it can in principle be renegotiated by whoever notices they are paying it.
Set beside the exclusion research, the two halves of a single exchange come into view. Ostracism prices non-membership at above d = 1.4 in a two-minute game with strangers. Asch prices membership at roughly a third of your public agreement with your own eyes. The Need to Belong literature, which is very large, covers only the first of those.