The science (or lack thereof) behind Field Sobriety Testing

You probably wonder what exactly are Field Sobriety Tests (FST’s), and where they came from. These tests are a series of "standardized" tests that are generally administered on the side of the road. The three most common tests are:

  • Horizontal Gaze Nystagmus (HGN), which looks at the movement of your eyes
  • Walk and turn
  • One Leg Stand

Where did FST's come from?

These tests were developed in the late 70’s to provide a “standard” series of tests for officers to give motorists who were suspected of driving while intoxicated. At the time, there were all sorts of “tests” that officers had come up with. Different tests were administered by different agencies, and there were even different tests within the same agency, depending on the particular officer doing the investigation.

In the late 1970s the federal government gave a grant to a research group called the Southern California Research Institute (SCRI) to come up with a procedure for administering field sobriety tests that was more reliable that the ones being used at the time. The tests that the group eventually came up with, by their own admission, were still far from perfect. The group’s own data showed that roughly half of subjects tested would have been arrested, despite their BAC being under the legal limit. Unsatisfied with these results, the federal government gave SCRI another crack at it. In 1981 they came up with some better data. This time roughly 30 percent of subjects would have been falsely arrested.

In 1981, SCRI published a report claiming that the barely passable 32 percent false arrest rate had been brought down to a confidence-inspiring 9 percent. While that sounds better, you need to know the way the tests were administered. When the test procedure was examined by independent experts, they discovered that a large percentage of the test subjects had blood alcohol levels so far over the legal limit that their performance on FSTs was nearly irrelevant. They also didn't administer the tests to individuals who had nothing to drink, so there is no baseline. That suggests that what field sobriety tests are really good for is identifying people with blood alcohol levels way over the legal limit.

The scientific basis for FST's

The big problem with Field Sobriety is that their scientific validity has never been verified. The tests were developed by an “interest group”, and the methodology was questionable. In the scientific field there are certain protocols and procedures that must be followed when doing any type of testing; think back to your High School science class. More importantly, results are not generally accepted until they have been peer reviewed. The field sobriety tests used every day across the county HAVE NEVER BEEN PEER REVIEWED. That sound unbelievable, but it’s the truth.

While FST’s purport to be “objective”, they are far from it. Each of the tests requires scoring, and how something is scored is largely subjective. This is not an issue in extreme cases, but can be in cases where the person may be just barely over the legal limit. The scenario that most people have in their heads of a drunk person is  a guy who, when asked to walk a line, wobbled along before falling flat on his face.

Unfortunately, that’s not the typical case. Instead, FST’s are used more often on the “borderline” cases, where an officer is not sure whether someone is legally intoxicated.  The ability to determine intoxication in the borderline cases is far more difficult.

How do people who aren't intoxicated on the tests perform?

Two researchers from Clemson University decided to do an experiment to see how good police officers were at distinguishing someone who is under the legal limit from someone who is too drunk to drive, based entirely on watching them perform field sobriety tests. Fourteen local police officers were shown videotapes of 21 subjects taking six common field sobriety tests and were asked to decide which were too intoxicated to drive.” On average, the police officers determined that 46percent of the subjects were legally intoxicated.

So how did they do? Not well, considering that not a single subject had consumed alcohol. None. The blood alcohol level of every subject was .00percent! This is a particularly disquieting result considering that, if the officers and pulled these individuals over, they would have arrested an innocent person half of the time.

In addition to performing field sobriety tests, the subjects in this study also performed a number of “normal abilities” tests, including counting from 1 to 10, walking normally, and reciting personal information (such as their Social Security number, driver’s license number, date of birth, home address and phone number). The police officers—who judged 46 percent of the subjects to be intoxicated from watching them perform FSTs—determined that only 15percent of the subjects were intoxicated when watching them perform these normal abilities tests. The moral of the story is this: compared to “normal” activities, field sobriety tests had the effect of making people appear drunk.

What does this all mean?

So what does all this mean? The takeaway should be that just because you fail the field sobriety tests, doesn’t mean you are legally intoxicated. Instead, there is at least some chance you might not be. Even if the tests are accurate 80% of the time, does it really make you feel better to know that only 20 people out of 100 go to jail who shouldn’t have? I’m pretty sure your answer would be no if you were one of the 20.

You yourself may have been a victim of an officer’s inability to interpret your performance on field sobriety tests, as well as the lack of sound science behind these tests. If you are fairly certain, or completely certain, that you were not driving with a BAC above the legal limit, but you still “failed” a battery of field sobriety tests, then this is precisely what happened to you. The best thing you can do is to find an attorney who knows the truth behind these tests.

If you want to talk to an attorney who understands Field Sobriety Testing, and who has received the training as the police officers, give us a call at 254-296-0020, or fill out the contact form on this page.