The marketing term “effective frequency” refers to the idea that a consumer has to see or hear an ad a number of times before its message hits home. Essentially, the more you say something, the more it sticks in－and possibly on－people’s heads. It doesn’t even have to be true－and that’s the problem. What advertisers call “effective frequency,” psychologists call the “illusory truth effect”: the more you hear something, the easier it is for your brain to process, which makes it feel true, regardless of its basis in fact.\n“Each time, it takes fewer resources to understand,” says Lisa Fazio, a psychology professor at Vanderbilt University. “That ease of processing gives it the weight of a gut feeling.” That feeling of truth allows misconceptions to sneak into our knowledge base, where they masquerade as facts. One example Fazio and her research team give is the belief that vitamin C can prevent colds, which many people have taken as a fact but is actually a misconception simply because it is long repeated.\nEven in the absence of endless repetition, we’re more likely to believe what we hear than to question it objectively, thanks to another psychological principle: confirmation bias.\n“In general, human beings, after hearing any claim, behave like naive scientists and tend to look for information that confirms the initial conjecture,” says Ajay Kalra, a marketing professor at Rice’s Jones Graduate School of Business. “In an interesting experiment, a group of consumers was told a leather jacket, Brand A, was very good. When they later examined several brands, they tended to spend more time looking at Brand A and evaluating it more highly than other brands.”\nThe same principle applies to a coffee company’s claim that its coffee is the “richest” in the world. “Confirmation bias typically applies to situations where information is ambiguous and hard to refute,” he explains. “The more often you hear a message, the more the confirmatory bias likely comes into play.”\nIt’s no wonder that many of us fall for false claims on social media, especially when we see them tweeted and retweeted again and again. How can we fight back? There are ways to lessen the influence of repeated claims. One of the best: don’t rely on a single source for information. Read stories from multiple news outlets and listen to a variety of opinions. Commit to staying open-minded, and consult with friends and colleagues whose perspectives differ. Take a second to consider how you know something is true. In this way, you can stymie the effects of repetition. It’s a great thing to do on social media: before you share something, take that second and pause. Otherwise, you risk becoming part of the echo chamber that keeps falsehoods circulating.