Illusory truth effect

The illusory truth effect (also known as the illusion of truth effectvalidity effecttruth effect, or the reiteration effect) is the tendency to believe false information to be correct after repeated exposure. This phenomenon was first identified in a 1977 study at Villanova University and Temple University. When truth is assessed, people rely on whether the information is in line with their understanding or if it feels familiar.

The first condition is logical, as people compare new information with what they already know to be true. Repetition makes statements easier to process relative to new, unrepeated statements, leading people to believe that the repeated conclusion is more truthful.

The illusory truth effect has also been linked to hindsight bias, in which the recollection of confidence is skewed after the truth has been received.

In a 2015 study, researchers discovered that familiarity can overpower rationality and that repetitively hearing that a certain fact is wrong can affect the hearer's beliefs. Researchers attributed the illusory truth effect's impact on participants who knew the correct answer to begin with, but were persuaded to believe otherwise through the repetition of a falsehood, to "processing fluency".

The illusory truth effect plays a significant role in such fields as election campaignsadvertisingnews media, and political propaganda.


Although the truth effect has been demonstrated scientifically only in recent years, it is a phenomenon with which people have been familiar for millennia. One study notes that the Roman statesman Cato closed each of his speeches with a call to destroy Carthage ("Ceterum censeo Carthaginem esse delendam"), knowing that the repetition would breed agreement, and that Napoleon reportedly "said that there is only one figure in rhetoric of serious importance, namely, repetition", whereby a repeated affirmation fixes itself in the mind "in such a way that it is accepted in the end as a demonstrated truth".

Others who have taken advantage of the truth effect have included QuintilianRonald ReaganBill ClintonGeorge W. BushDonald Trump, and Marcus Antonius in Shakespeare's Julius Caesar.

Advertising that repeats unfounded claims about a product may boost sales because some viewers may come to think that they heard the claims from an objective source. The truth effect is also used in news media and is a staple of political propaganda.


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