"I judge repeated information as being more likely to be true than new information."
The repetition of a piece of information can increase its perceived credibility, compared to a new piece of information. We tend to (irrationally) reinforce our belief in information if it is presented to us multiple times. When we are not familiar with a topic, and where the situation is ambiguous, it is normal to look for clues to judge the truth or falsity of a piece of information. The source of the information, or the context wherein the information is received, can be good external markers to evaluate the truth or falsity in a given situation. However, repetition itself should not serve as a signal of truth, since it does not add anything new to the conversation in terms of credibility. For this reason, the repetition bias is also called the “illusory truth effect” .
Many studies have shown that the belief in false statements tends to increase when they are heard more than once. In March of 2018, Donald Trump falsely announced to the media that the construction of a wall had begun at the southern border of the United States. This false information was repeated more than 200 times by the president in the following two years. If one single repetition can increase the belief in this type of claim, it is easy to see that it is an inexpensive political strategy for the parties which have a vast public platform, and fairly noxious for democracy, insofar as repetition by itself is enough to convince the population and influence political behaviors.
The main explanation put forward for this bias is related to the ease with which our brain processes repeated information . When a piece of information is repeated, it becomes more familiar, which pushes us to believe that it is likely to be true. Researchers have shown that this is the case even when the information is implausible, or when we know that it is false . Another hypothesis is that we interpret repetition as a clue that the information comes from multiple sources, which increases the belief in that piece of information.
The effects of repetition on belief is a crucial issue in an age where information is more and more accessible, and because clues such as the source and context of a piece of information are not always readily available. A large proportion of the population takes its information from social media and online media, where the content can be repeatedly shared. In this respect, it is easy to see how interested parties can use repetition to increase the credibility of a piece of false information. The repetition bias can have significant impacts on behaviors relating to voting or health, for instance. This effect could even render information from satirical sites more credible. As such, repeatedly sharing information on Facebook which we judge to be false could be unconsciously making our friends more likely to believe that information.
Thoughts on how to act in light of this bias
The repetition bias is thought to be exacerbated when we are not paying attention to the information; concentrating could help reduce its impact.
Reading the entirety of an article when time permits, rather than just the title.
Finding information about the information in question, even when we judge it as being true (what is the source; was it written by journalists?).
How is this bias measured?
The classic way of measuring the repetition bias consists in an experiment which is divided in two phases. In phase 1, the participants must read 20 statements about topics with which they are not familiar, and judge to which extent they believe each sentence to be true or false. In phase 2, the participants again read 20 statements, 10 of which are taken from phase 1 (and therefore repeated), 10 of which are new. The researchers compare the judgements given for each statement in phases 1 and 2 for the 10 repeated items. If the belief in the statements has increased the second time they are read, there is a repetition bias.
This bias is discussed in the scientific literature:
This bias has social or individual repercussions:
This bias is empirically demonstrated:
 Dechêne, Alice, Christoph Stahl, Joachim Hansen & Michaela Wänke (2010). The truth about the truth: A meta-analytic review of the truth effect. Personality and Social Psychology Review 14(2): 238-257. (Meta-analysis)
 Begg, Ian Maynard, Ann Anas & Suzanne Farinacci (1992). Dissociation of processes in belief : Source recollection, statement familiarity and the illusion of truth. Journal of Experimental Psychology : General 121(4): 446-458.
 Fazio, Lisa K., Nadia M. Brashier, Keith B. Payne & Elizabeth J. Marsh (2015). Knowledge does not protect against illusory truth. Journal of Experimental Psychology : General 144(5) : 993-1002.
Individual level, Availability heuristic, Need for cognitive closure
Continued misinformation effect
Mere exposure effect
Implied truth effect
Cloé Gratton is a PhD candidate in psychology at the Université du Québec à Montréal. She is affiliated to the Laboratoire des processus de raisonnement. She is also co-founder of Shortcuts.