- The truth effect refers to the tendency to believe things that have been repeated.
- The truth effect is a highly reliable phenomenon
- People are particularly likely to underestimate the size of this effect for themselves.
Research spanning several decades demonstrates that you are more likely to think the information that is repeated to be true than the information you hear only once. This happens when you actually hear the information several times, and also when you believe that the information is going to be repeated. You assume that if people are going to put in effort to repeat a statement, this reflects the truth of the statement.
Simply repeating some piece of information does not actually make it true, but this tendency—also called the truth effect—is a bias that can lead you to draw the wrong conclusions. An important step in counteracting the negative influence of biases in thinking is to be aware of them.
To what degree are people aware of the truth effect? This question was addressed in a paper in the journal Cognition slated to appear in early 2024 by Simone Mattavelli, Jeremy Bena, Olivier Corneille, and Christian Unkelbach.
In the critical study in this paper, participants did two sessions. In one session, they read about a hypothetical study in which people were exposed to trivia statements (Vatican City is the smallest country in the world) and then were asked whether both statements they had heard before as well as new statements were true. They were asked to predict the proportion of each statement that would be judged as true. They did this both as a prediction of other people’s performance as well as a prediction of how they would do in this study.
At another session a few days later, participants actually performed this study, reading a set of 20 trivia statements and then judging the truth of 40 statements, half of which were the ones they saw earlier and the other half of which were new.
This study did replicate the well-known truth effect. People were more likely to judge statements they had seen before as true than statements that were new. Two interesting findings emerged from the predictions. First, participants tended to underestimate the size of the truth effect for everyone. That is, while people did expect some difference in judgments between the statements seen before and those that were new, they thought this difference would be smaller than it actually was. Second, participants were more wrong when predicting their own performance compared to predicting the performance of another person. That is, people more significantly underpredicted the truth effect for themselves compared to that for other people.
The important thing to take from this study is that we all need to be educated: being exposed to a piece of information can have a significant impact on our sense that the information is true and that hearing this information repeatedly can increase this sense. We also need to be aware of our susceptibility to this bias.
This work is particularly important in light of the amount of misinformation present in social media. Many people are vested in influencing public opinion about political and economic matters. Flooding social media feeds with misinformation will lead people to believe this information is true just because it is stated. Recognizing that we are all susceptible to this influence of repeated information should lead us to mistrust our intuition about what is true and to look up important information prior to using it to make important judgments and decisions.
Dechêne, A., Stahl, C., Hansen, J., & Wänke, M. (2010). The Truth About the Truth: A Meta-Analytic Review of the Truth Effect. Personality and Social Psychology Review, 14(2), 238-257.
Simone Mattavelli, Jérémy Béna, Olivier Corneille, & Christian Unkelbach (2024). People underestimate the influence of repetition on truth judgments (and more so for themselves than for others), Cognition, 242, 105651.