Confirmation Bias

One of America’s greatest scientists summarized confirmation bias well when he quipped, “I wouldn’t have seen it if I didn’t believe it.”That scientist was the great Hall of Famer and New York Yankee baseball player Yogi Berra. How do we know Yogi Berra said that? One of us once heard someone say that he did, and it sounds like the kind of thing that has been attributed to him. Of course, there are those who say that Yogi didn’t say many of the things attributed to him and that there are actually perfectly logical explanations for some of the seemingly nonsensical statements he allegedly did utter. But we don’t care about any of that. We love the line, it makes our point well, and we are going to stick to the Yogi attribu¬tion no matter what kind of disconfirming evidence crops up. As Yogi might have said, “When you come to a piece of evidence that doesn’t agree with what you already believe, tear it to shreds and then ignore it.” Confirmation bias refers to our tendency to attend only to information that agrees with what we already think is true. Notice that we did not simply say that this bias involves ignoring evidence that is incompatible with our beliefs but rather that it is an active process in which we selectively pay attention to those things that confirm our hypotheses. Confirmation bias is responsible for not only a great deal of denial of scientific evidence but also the actual generation and maintenance of incorrect scientific information. That is, scientists, doctors, and public health experts are as prone as anyone else is to “seeing what we believe,” making it especially difficult to help people sort out what is true science from the mistakes and outright fabrications. As we will see, confirmation bias is strongly rooted in primitive needs and emotion and therefore not amenable to correction merely by reciting facts. Although confirmation bias is irrational in the sense that it does not take into consideration evidence, it is still frequently adaptive and even necessary.