Not knowing what we don't know leads to bad decision making, says Cornell study

David Dunning

Dozens of studies agree: Most people overrate their own abilities. This tendency can have severe consequences: young adults making poor decisions about college and careers, pilots flying into storms and overconfident doctors making erroneous diagnoses.

According to a Cornell University expert on self-insight who has published two studies on the topic as well as a new book, "Over a lifetime, people base thousands of decisions on impressions of their skill, knowledge, expertise, talent, personality and moral character." However, says David Dunning, professor of social psychology at Cornell, "People's capacity to evaluate themselves and predict their behavior is usually quite modest and often much more meager than common intuition would lead one to believe."

Dunning has conducted dozens of studies showing that people often hold overinflated views of their expertise and character. His latest study in the most recent issue of Psychological Science in the Public Interest (Vol. 5:3) shows that this psychological phenomenon can have far-reaching implications in health, education and the workplace. His co-authors are Chip Heath of Stanford University and Jerry Suls of the University of Iowa.

"People tend to believe their personal risk of becoming ill from food poisoning, SARS or HIV, for example, is lower than other peoples' risks. Students consistently think they've done better on exams than they really have, and surgical residents think they can perform procedures much better than their supervisors think the residents can," said Dunning. "Likewise, from the office cubicle to the executive boardroom, people tend to hold overly inflated self-views that are only modestly related to actual performance. Often, other people -- subordinates, peers and superiors -- can make much better judgments about others than themselves."

To get a better handle on why people's self-perceptions are so inaccurate, Dunning and former graduate student Deanna Caputo, Ph.D. '04, who now works at BAE Systems in Virginia, conducted a series of five studies suggesting that people overrate their skills, in part, not because of inflated egos but because they have little or no insight into a specific class of errors they make -- their errors of omission. Participants in the studies rated themselves on how well they did on word games, visual puzzles, grammar tasks and evaluations of research methodologies. In a variation, volunteers were informed about the solutions they had missed and then asked to rate their performance again.

The New Yorker Collection.

Dunning and Caputo found that although participants were perfectly aware of solutions they had generated in the tasks they confronted, they were completely unable to predict how many additional solutions they had missed. Not surprisingly, when asked to evaluate themselves, participants' self-evaluations gave these errors of omission no weight. Self-evaluations changed, however, when participants' errors of omission were pointed out to them. "We found that when participants were given explicit information about their errors of omission, they gave those errors as much weight as they did to the solutions they found," said Dunning.

In another article, he and Caputo conclude in the Journal of Experimental Social Psychology (September 2005; available online at that people are poor self-evaluators, in part, because they have no awareness of gaps in their knowledge or of the range of solutions they could apply to problems but do not. In short, although people know what they know, they are unaware of the universe of what they do not know.

"It's banal in one sense but completely profound in another. We don't know what we do not know. Thus, we do not have all the information we need to make accurate self-judgments. And it's not a surprise that it's hard to know yourself, because you never have all the information you need to do so, and people are often not aware of that fact," said Dunning. "This may seem self-evident, but it's not an insight people realize on a day-to-day basis.

"You have to worry about the stuff you don't realize you don't know. It's these unknown unknowns that keep NASA officials up at night. It is what you are unaware of that you really have to find out."

What all the studies show, he said, is that people need to be more cautious about what they know and do not know about themselves and should try to adjust their self-views and predictions accordingly.

The studies were supported, in part, by the National Institute of Mental Health.

Dunning's new book

book cover

Dunning has published a new book on the topic, "Self-Insight: Roadblocks and Detours on the Path to Knowing Thyself" (Psychology Press: 2005). It details the scientific evidence for the inaccuracies of the impressions people hold of themselves and why it is surprisingly difficult to form accurate impressions of self.

"Even with all the time we spend with ourselves and all the motivation to achieve accurate self-understanding, we reach flawed and sometimes downright wrong conclusions about ourselves," Dunning writes in the book.

The book explores:

  • Why people are such poor judges of their competencies and skills in social and intellectual areas;
  • How people develop their self-perceptions of skill and accuracy, if not from performance;
  • Why life experiences and feedback don't always help people develop more accurate impressions of self;
  • Why people believe they are more unique and special than they really area;
  • Why people so often believe they are ethically superior to others;
  • Why mistaken predictions of self may sometimes have nothing to do with faulty self-knowledge, but rather be more of a function of misunderstanding the situations we put ourselves in.

"Achieving accurate self-judgment is inherently difficult, and many question whether accurate self-evaluations are even possible," Dunning said. "Nevertheless, there are tools that people do have at their disposal to evaluate themselves, but they tend to ignore them."

These include paying close attention to past outcomes, looking to others as a crucial source of information about oneself and paying close attention to how others do the things that you want to do better. "Using your peers as mentors can be very useful because everybody has a different set of competencies," Dunning said.


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