Friday, May 28, 2004

Ideas: Confirmation Bias

This essay is from The Skeptic's Dictionary.



Confirmation Bias

"It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than by negatives." --Francis Bacon

Confirmation bias refers to a type of selective thinking whereby one tends to notice and to look for what confirms one's beliefs, and to ignore, not look for, or undervalue the relevance of what contradicts one's beliefs. For example, if you believe that during a full moon there is an increase in admissions to the emergency room where you work, you will take notice of admissions during a full moon, but be inattentive to the moon when admissions occur during other nights of the month. A tendency to do this over time unjustifiably strengthens your belief in the relationship between the full moon and accidents and other lunar effects.

This tendency to give more attention and weight to data that support our beliefs than we do to contrary data is especially pernicious [evil] when our beliefs are little more than prejudices. If our beliefs are firmly established upon solid evidence and valid confirmatory experiments, the tendency to give more attention and weight to data that fit with our beliefs should not lead us astray as a rule. Of course, if we become blinded to evidence truly refuting a favored hypothesis, we have crossed the line from reasonableness to closed-mindedness.[We are closed-minded when there is evidence that says we are wrong.]

Numerous studies have demonstrated that people generally give an excessive amount of value to confirmatory information, that is, to positive or supportive data. The "most likely reason for the excessive influence of confirmatory information is that it is easier to deal with cognitively" (Gilovich 1993). It is much easier to see how a piece of data supports a position than it is to see how it might count against the position. Consider a typical ESP experiment or a seemingly clairvoyant dream: Successes are often unambiguous or data are easily massaged to count as successes, while negative instances require intellectual effort to even see them as negative or to consider them as significant. The tendency to give more attention and weight to the positive and the confirmatory has been shown to influence memory. When digging into our memories for data relevant to a position, we are more likely to recall data that confirms the position.

Researchers are sometimes guilty of confirmation bias by setting up experiments or framing their data in ways that will tend to confirm their hypotheses. They compound the problem by proceeding in ways that avoid dealing with data that would contradict their hypotheses. For example, parapsychologists are notorious for using optional starting and stopping in their ESP research. Experimenters might avoid or reduce confirmation bias by collaborating in experimental design with colleagues who hold contrary hypotheses. Individuals have to constantly remind themselves of this tendency and actively seek out data contrary to their beliefs. Since this is unnatural, it appears that the ordinary person is doomed to bias.

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My comments:
Einstein built theories. He must have also been aware of confirmation bias. He used to say that if he were right you would see so-and-so, but if he were wrong you would see such-and-such. When trying to reach the truth -- which can be hard to find -- we need to follow Einstein's example. That is, not only say what we would find if we are right, but also say what we would find if we are wrong.



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