In psychology, the false-consensus effect or false-consensus bias is a cognitive bias whereby a person tends to overestimate how many people agree with him or her. There is a tendency for people to assume that their own opinions, beliefs, preferences, values, and habits are “normal” and that others also think the same way that they do. This cognitive bias tends to lead to the perception of a consensus that does not exist, a “false consensus”. This false consensus is significant because it increases self-esteem. The need to be “normal” and fit in with other people is underlined by a desire to conform and be liked by others in a social environment.

Within the realm of personality psychology, the false-consensus effect does not have significant effects. This is because the false-consensus effect relies heavily on the social environment and how a person interprets this environment. Instead of looking at situational attributions, personality psychology evaluates a person with dispositional attributions, making the false-consensus effect relatively irrelevant in that domain. Therefore, a person’s personality potentially could affect the degree to which the person relies on false-consensus effect, but not the existence of such a trait.

The false-consensus effect is not necessarily restricted to cases where people believe that their values are shared by the majority. The false-consensus effect is also evidenced when people overestimate the extent to which their particular belief is correlated with the belief of others. Thus, fundamentalists do not necessarily believe that the majority of people share their views, but their estimates of the number of people who share their point of view will tend to exceed the actual number.

This bias is especially prevalent in group settings where one thinks the collective opinion of their own group matches that of the larger population. Since the members of a group reach a consensus and rarely encounter those who dispute it, they tend to believe that everybody thinks the same way.

Additionally, when confronted with evidence that a consensus does not exist, people often assume that those who do not agree with them are defective in some way. There is no single cause for this cognitive bias; the availability heuristic, self-serving bias, and naïve realism have been suggested as at least partial underlying factors.

The false-consensus effect can be contrasted with pluralistic ignorance, an error in which people privately disapprove but publicly support what seems to be the majority view (regarding a norm or belief), when the majority in fact shares their (private) disapproval. While the false-consensus effect leads people to wrongly believe that the majority agrees with them (when the majority, in fact, openly disagrees with them), the pluralistic ignorance effect leads people to wrongly believe that they disagree with the majority (when the majority, in fact, covertly agrees with them). Pluralistic ignorance might, for example, lead a student to engage in binge drinking because of the mistaken belief that most other students approve of it, while in reality most other students disapprove, but behave in the same way because they share the same mistaken (but collectively self-sustaining) belief. In a parallel example of the false-consensus effect, a student who likes binge drinking would believe that a majority also likes it, while in reality most others dislike it and openly say so.