In Plato's Republic, a Socratic dialogue concerning the definition of justice, Socrates states, "As for me, all I know is that I know nothing." Thousands of years later in the modern scientific age, we would do well to adopt that sort of thinking. New research shows that the more people think they know about a topic, the more likely they are to state facts that are completely false — a process called "overclaiming," according to the study, published in Psychological Science.

For the study, researchers designed a series of experiments to assess people's claims to knowledge, with the goal of seeing how people perceived their own knowledge. In one set of experiments, for example, researchers tested whether participants who believed they were experts in personal finance would be more likely to claim they knew about "fake" financial terms.

One hundred participants were asked to rate their knowledge of personal finance in addition to noting how familiar they were with 15 financial terms. Most of these terms were real, such as inflation and home equity. But there were also made-up terms, such as "pre-rated stocks" and "annualized credit," which were intended to blend in with the rest. As the researchers predicted, those who believed they knew the most about finance were the most likely to claim they knew what the fake terms were.

"The more people believed they knew about finances in general, the more likely they were to overclaim knowledge of the fictitious financial terms," said Stav Atir, study author and psychological scientist at Cornell University, in a statement. "The same pattern emerged for other domains, including biology, literature, philosophy, and geography."

In a separate experiment, one set of 49 participants were warned that some terms on the list weren't real. Yet, despite being aware there was a trick in the experiment, those who believed they were experts were still more likely to claim familiarity with the fake terms.

Then, in another experiment, the researchers used a geography test to prove people were claiming knowledge of fake terms because of their own perceived expertise. The participants were randomly assigned an easy quiz on iconic American cities, a difficult quiz on obscure cities, or no quiz at all. They found that participants who finished the easy quiz were most likely to feel like experts, and they even reported being more knowledgeable than those in the other groups.

These participants moved on to another test in which they were asked to rate their familiarity with cities and regions from a list, which contained both real and a few fake names. Of course, the more well-known cities were recognized, but less well-known cities and regions weren't recognized. What's more, those who claimed they were more self-confident in their geographical knowledge were more likely to claim to be knowledgeable about non-existent places, such as Cashmere, Ore.

Part of being knowledgeable is recognizing not knowing something exposes new opportunities for learning. When you overclaim, it means you can't recognize the limit of your understanding, and this may result in unwanted consequences when it comes to making decisions about finances and politics. This research shows that it is not just ignorance that clouds judgment, it is also the illusion of knowing.

Source: Atir S, Rosenzsweig E, Dunning D. When Knowledge Knows No Bounds: Self-Perceived Expertise Predicts Claims of Impossible Knowledge. Psychological Science. 2015.