While I have a bachelor’s degree in psychology, I’m by no means a psychologist. Nor can I say that there’s much that I remember from my college studies except those things that are proving to be particularly relevant in my law career. One of those things is the “confirmation bias.”
The confirmation bias occurs when a person has beliefs or expectations and unconsciously seeks out and interprets information to confirm those beliefs and expectation while ignoring contradictory information. Put in simple terms, people see what they want to see.
The confirmation bias is proving to be particularly relevant in criminal law because unfortunately, it affects law enforcement decisions, particularly in DUI cases, more often than I’d like to admit.
Although proven to be unreliable, the purpose of field sobriety tests are to allow officers to obtain information sufficient to establish probable cause that a person has been driving drunk. However, often is the case that the officers have already decided that a person is guilty of drunk driving even before the field sobriety tests are conducted.
Regardless of how the DUI suspect performs on the field sobriety tests, the officers will interpret the performance to justify their own expectations about the DUI suspect. This is exactly why I always advise my clients and anyone else who may happen to find themselves in the unfortunate predicament of being stopped on suspicion of DUI: never agree to perform field sobriety tests.
While I’ve seen this psychological phenomenon play out in more than a number of California DUI cases that I’ve handled, until recently I was unaware that the confirmation bias effect on law enforcement in DUI cases has actually been empirically tested.
In 1977, the National Highway Transportation Safety Administration (NHTSA) commissioned a study by the Southern California Research institution to test the best field sobriety tests. Ten police officers observed several hundred subjects who were given varying amounts of alcohol. Neither the officers nor the participants knew how much alcohol was ingested by each participant. Based on the subject’s performance on the field sobriety test, the officers incorrectly identified subjects as having a blood alcohol content above 0.10 percent a whopping 47 percent of the time.
In 1994, Dr. Spurgeon Cole, a researcher at Clemson University, conducted a study which tends to confirm the 1977 study. Dr. Cole videotaped 21 sober individuals performing six field sobriety tests. Fourteen police officers, with a median experience level of 11.7 years, viewed the videotapes. I would be remiss not to mention that all of the officers had completed state-mandated DUI detection training courses. Even though the subjects were completely sober, the officers determined that the subjects were too drunk to drive an astonishing 46 percent of the time.
Leo Tolstoy once said, “The most difficult subjects can be explained to the most slow-witted man if he has not formed any ideas of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of a doubt, what is laid before him.”