Thursday, May 18, 2017

Can You Either Confirm or Deny?: Confirmation Bias

Learning By Doing

Let's play a game. Unfortunately, I have to send you away from this page. But go play and come right back! 

Reflection Questions
  • did you do? 
  • Did you figure out the rule that governs the sequence of numbers? 
  • What problem-solving strategies did you use? 
  • Was there something that you wish you would have done differently? 

The Two Flavors of Confirmation Bias

Informally, the confirmation bias is the tendency to seek evidence that is consistent with your beliefs. The more personal the beliefs, the stronger the bias. More formally, there are two parts to the definition. The first part is "searching for confirmatory evidence," and the second part is "selectively interpreting the data to fit with one's hypothesis."

Selective Search of Data: The Luminiferous Ether

The number generation game that you played at the beginning of this post is a good example of looking for evidence that conforms to your initial hypothesis [1]. It's a tricky puzzle, and an overwhelming majority of people submit triples that confirm their suspicions. If this describes you, then you are not alone.

Confirmation bias is not relegated to the psychological laboratory. It also operates in the real world. Scientists, for example, often have a vested and personal interest in seeing their hypotheses confirmed by their data. A classic example in the history of science is the search for evidence of the “luminiferous ether." Up until the 19th century, it was believed that this was the substance that carried light. Like sound, it was believed that light needed a medium through which to propagate. Finally, in 1887, Albert Michelson and Edward Morley conducted a famous experiment that conclusively disconfirmed the existence of the ether [2]. Before that experiment, there was a lot of effort invested in finding evidence for this mysterious ether.

Bottom line: The data are selectively collected and disconfirmatory evidence is deemed irrelevant.

Selective Interpretation of Data: The People v. O. J. Simpson 

The O. J. Simpson trial is a good example of selectively interpreting evidence to support your position or claim [3]. As in most trials, there was evidence that nobody can deny: blood at O. J.'s house contained the DNA of Nicole Brown Simpson. There was blood found in O. J.'s white Ford Bronco that matched both Nicole and Ron Goldman's DNA. O. J. Simpson had been arrested for physically assaulting Nicole. These are all incontrovertible facts. However, the defense and prosecution interpreted the data differently. The defense said that the blood samples were placed there by a racist LAPD cop. The defense claimed that the blood was not placed there, but was a result of the murders and subsequent coverup by O. J.

Bottom line: The data are right, but the interpretation of the data are subject to dispute.

The S.T.E.M. Connection

There are implications of the confirmation bias for the classroom as well. In the mid- to late-1960's, educational psychologists experimentally manipulated teachers' expectations of their students. They were told that certain students were about to experience a learning "spurt" (or not). They randomly selected kids to be in the "spurt" condition (or not). 

What did they find? They found that teacher expectations had a measurable impact on the number of IQ points the students gained over the course of an academic year. The effect was particularly strong for kids in first and second grade [4]. Although the authors did not provide a mechanism, we might expect that the confirmation bias was at work. Every time a child in the spurt condition did something notable, it confirmed that teacher's expectation. If the student failed to live up to her expectation, then you might imagine the teacher was able to explain away her behavior (e.g., she was just having a bad day).

Confirmation bias plagues us all, and it can be difficult to avoid. Given that, it is important to experience it first hand, receive feedback when it does happen, and practice looking for and interpreting evidence that goes against one's beliefs. Only then can we get a true picture of the world.  

Share and Enjoy!

Dr. Bob

Going Beyond the Information Given

[1] Wason, P. C. (1960). On the failure to eliminate hypotheses in a conceptual task. Quarterly journal of experimental psychology, 12(3), 129-140.

[2] Motta, L. (2007) Michelson-Morley experiment. Retrieved from

[3] Nickerson, R. S. (1998). Confirmation bias: A ubiquitous phenomenon in many guises. Review of General Psychology, 2(2), 175.

[4] Rosenthal, R., & Jacobson, L. (1968) Pygmalion in the classroom. New York: Hold, Rinehart and Winston.