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. You usually assume that if people put in effort to repeat a statement, this reflects the truth of the statement. This tendency-also called the truth effect-is a bias （偏见） that can lead you to draw incorrect conclusions.
To what degree are people aware of the truth effect? This question was addressed in a paper in the journal Cognition early this year.
In the critical study in this paper, participants did two sessions. In one session, they read about a hypothetical （虚构的） study in which they were exposed to some statements and then were asked whether both statements they had heard before as well as these new statements were true. They were asked to predict the proportion （比例） 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 statements in the hypothetical study again and then judging the truth of altogether 40 statements, half of which were from the hypothetical study 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 prediction. First, participants tended to underestimate the size of the truth effect for everyone. T hat is, while they 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 more significantly underpredicted the truth effect for themselves compared to that for other people.
This study is particularly important in light of the amount of misinformation present in social media. Many people have the power to influence public opinion about important 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 （直觉） about what is true and to look up important information prior to using it to make important judgments and decisions.
