The third-person effect hypothesis states that a person exposed to a persuasive communication in the mass media sees it as having a greater effect on others than on himself or herself (Davison, 1983). This is known as the perceptual hypothesis, but there is also a behavioral hypothesis predicting that perceiving others as more vulnerable increases support for restrictions on mass media.
The third-person effect hypothesis also argues that people are compelled themselves to take action after being exposed to a persuasive message but this action might not be due to the message itself but to the anticipation of the reaction of others. This action is unpredictable and it might be either in conformity with the message or counter to it.
Usually, the effects considered are about general media influence, but valence of the message also affects the effect size. Messages with undesirable consequences of persuasion increase the effect size and messages with desirable consequences decrease or even reverse the effect, as in someone believing that they are more able than others to follow a promoted healthy diet.
A meta-analysis of the perceptual hypothesis estimated the overall effect size to be large (r=.50) and stronger among college students (Paul, Salwen & Dupagne, 2000). A number of scholars have speculated that "experts" are particularly likely to overemphasize the effects of the media on others (Diamond, 1978).
The third-person effect, specially its behavioral hypothesis, is important to issues of censorship. Censors seldom admit to having been adversely affected by the information they prohibit even if they have been exposed to it numerous times. Usually, they claim, it is the general public that needs to be protected, not them (Davison, 1983).