According to a 1991 study (PDF) by Dr. Spurgeon Cole at Clemson University, field sobriety tests give a police officer about a 50-50 chance of accurately predicting whether a driver is intoxicated. Dr. Cole and his team videotaped 21 individuals performing common field sobriety tests and asked 14 police officers to judge whether any were too intoxicated to drive. The officers decided that 46% of the participants were unfit to drive, and presumably, had they actually been driving, they would have been asked to submit to some form of chemical testing. What Dr. Cole did not tell the officers was that none of the 21 participants in the study had anything to drink before performing the field sobriety tests.
It's not very comforting to know that field sobriety tests are about as effective in detecting drunk drivers as flipping a coin. However, this is much more comforting than the results of a 2007 study by the International Council on Alcohol Drugs & Traffic Safety (ICADTS), which showed that police officers correctly perform Standardized Field Sobriety Testing only 3% of the time. Standardized Field Sobriety Tests (or SFST's) are a battery of three field sobriety tests and require specialzed training. These tests are the Horizontal Gaze Nystagmus test (the HGN - or follow the pen with your eyes test), the Walk and Turn test (WAT) and the One Leg Stand test (OLS). Many departments in the area now use these tests.
The 2007 study analyzed 350 videotaped encounters of police officers administering SFSTs to suspected drunk drivers. The results are shocking. The HGN test was properly administered 7% of the time. The WAT test was properly administered 19% of the time. The OLS was properly administered 50% of the time. What is even worse than these results is the correct percentage when looking at the battery of tests given in each of the 350 encounters (and remember, the idea of SFSTs is that these three specific tests are to be given together). The battery of tests was properly administered only 3% of the time. That is not a typo.
These tests simply do not predict with any semblence of accuracy whether a person is intoxicated. For a police officer, administering them in a controlled, classroom setting is not quite like administering them at 3:00 a.m. in a dimly lit area when it's 20 degrees out and you're exhausted from being in court all day.
