The Psychology Today Website states
Repeat a lie often enough and people will come to believe it.
The Illusory Truth Effect
Many of us are familiar with the quotation, “Repeat a lie often enough and people will eventually come to believe it.”
Not ironically, the adage — often attributed to the infamous Nazi Joseph Goebbels — is true and has been validated by decades of research on what psychology calls the “illusory truth effect.” First described in a 1977 study by Temple University psychologist Dr. Lynn Hasher and her colleagues, the illusory truth effect occurs when repeating a statement increases the belief that it’s true even when the statement is actually false.1
Subsequent research has expanded what we know about the illusory truth effect. For example, the effect doesn’t only occur through repetition but can happen through any process that increases familiarity with a statement or the ease by which it’s processed by the brain (what psychologists in this context refer to as a statement’s “fluency”). For example, the perceived truth of written statements can be increased by presenting them in bold, high-contrast fonts2 or when aphorisms are expressed as a rhyme.3
According to a 2010 meta-analytic review of the truth effect (which applies to both true and false statements),4 while the perceived credibility of a statement’s source increases perceptions of truth as we might expect, the truth effect persists even when sources are thought to be unreliable and especially when the source of the statement is unclear. In other words, while we typically evaluate a statement’s truth based on the trustworthiness of the source, repeated exposure to both information and misinformation increases the sense that it’s true, regardless of the source’s credibility.
The illusory truth effect tends to be strongest when statements are related to a subject about which we believe ourselves to be knowledgeable,5 and when statements are ambiguous such that they aren’t obviously true or false at first glance.4 It can also occur with statements (and newspaper headlines) that are framed as questions (e.g. “Is President Obama a Muslim?”), something called the “innuendo effect.”6
But one of the most striking features of the illusory truth effect is that it can occur despite prior knowledge that a statement is false7 as well as in the presence of real “fake news” headlines that are “entirely fabricated…stories that, given some reflection, people probably know are untrue.”8 It can even occur despite exposure to “fake news” headlines that run against one’s party affiliation. For example, repeated exposure to a headline like “Obama Was Going to Castro’s Funeral—Until Trump Told Him This” increases perceptions of truth not only for Republicans but Democrats as well.8 And so, the illusory truth effect occurs even when we know, or want to know, better.
In summary, psychology research has shown that any process that increases familiarity with false information — through repeated exposure or otherwise — can increase our perception that the information is true. This illusory truth effect can occur despite being aware that the source of a statement is unreliable, despite previously knowing that the information is false, and despite it contradicting our own political affiliation’s “party line.”
References
1. Hasher L, Goldstein D, Topping T. Frequency and the conference of referential validity. Journal of Verbal Learning and Verbal Behavior 1977; 16:107-112.
2. Reber R, Schwarz N. Effects of perceptual fluency on judgments of truth. Consciousness and Cognition: An International Journal 1999; 8:338-342.
3. McGlone MS, Tofighbakhsh J. Birds of a feather flock conjointly (?): Rhyme as reason in aphorisms. Psychological Science 2000; 11:424-428.
4. Dechene A, Stahl C, Hansen J, Wanke M. The truth about the truth: a meta-analytic review of the truth effect. Personality and Social Psychology Review 2919; 14:238-257.
5. Arkes HR, Hackett C, Boehm L. The generality of the relation between familiarity and judged validity. Journal of Behavioral Decision Making 1989; 2:81-94.
6. Wegner DM, Wenzlaff R, Kerker RM, Beattie AE. Incrimination through innuendo: can media questions become public answers? Journal of Personality and Social Psychology 1981; 40:5:822-832.
7. Fazio LK, Brashier NM, Payne BK, Marsh EJ. Knowledge does not protect against illusory truth. Journal of Experimental Psychology: General 2015; 144:993-1002.
8. Pennycook G, Cannon TD, Rand DG. Prior exposure increases perceived accuracy of fake news. Journal of Experimental Psychology: General 2018; 147:1865-1880.