By Collin County Criminal Defense Lawyer Jeremy Rosenthal
Confirmation bias is a psychological phenomenon whereby people have a tendency to selectively prefer information which confirms their pre-existing beliefs and hypotheses.
Why is this important in criminal law? Because every case involves investigation in one way or another. Police officers can and do fall into the confirmation bias trap. Classic signs of confirmation bias include ignoring evidence that contradicts the initial impression of the officer and interpreting neutral facts or exculpatory facts as evidence of guilt among others.
Psychologists have conducted studies on confirmation bias. In one study, test subjects were given fake police files which weakly incriminated a particular suspect. Later evidence showed that perhaps a second suspect was the culprit and that the original information was false. Not surprisingly, the subjects fell into several confirmation bias traps. They rejected evidence inconsistent with the innocence of the original suspect, they viewed neutral or ambiguous evidence as evidence of the original suspect's guilt, and finally the suspects ignored evidence pointing to the guilt of the second suspect in favor of evidence against the first suspect.
I see confirmation bias all the time from law enforcement during investigations. You can tell when it's going on in certain opinion-oriented cases such as DWI when you read an offense report which omits or wholly ignores evidence that contradicts the officer's findings. Often times police will take neutral facts (like where they describe a person as 'nervous' at a traffic stop) and attempt to spin that into evidence of guilt. Obviously that is non-sense as many people are nervous when confronted by authority figures like a police officer in uniform -- not just criminals.
Dealing with confirmation bias takes a skilled trial lawyer. Jurors must be educated during jury selection about confirmation bias and be show the practical example of confirmation bias in action when the officer holds firm to his opinion despite all the contrary evidence.
*Jeremy F. Rosenthal is an attorney licensed to practice in the State of Texas. Nothing in this article is intended to be legal advice. For specific legal advice for your own matter you should contact an attorney.