How Accurate are Field Sobriety Tests?

If you have recently been arrested for driving under the influence, you were likely asked to take a field sobriety test when you were first stopped by a police officer. The officer probably noticed you exhibiting signs that you were intoxicated while driving your vehicle, which gave them “reasonable suspicion” to stop you. In order to establish full “probable cause,” they likely conducted these tests with you, which confirmed their suspicions and allowed them to make the arrest. However, many people are shocked at just how many mistakes are made when it comes to wrongful DUI arrests, along with just how shockingly inaccurate field sobriety tests are.

The Three Most Common Field Sobriety Tests

Back in the late 1970s, the NHTSA and Southern California Research Institute conducted a series of studies in order to establish the most accurate and reliable field sobriety tests, as well as develop standards for administering them. The goal was to minimize errors in issuing these tests and successfully prosecute people who were driving drunk. The SCRI came up with three tests: the horizontal gaze nystagmus test, the one-leg stand test, and the walk and turn test. While combined with each other yielded better results, these tests on their own are surprisingly inaccurate.

Horizontal Gaze Nystagmus
In this test, the officer holds an object up at about eye level to the driver and then asks them to follow it with their eyes while keeping their head still. An intoxicated individual will lose some of their ability to control their eye muscles, resulting in twitching. However, those who are dyslexic or have other inhibitions will have difficulty performing this task, making it accurate only about 77 percent of the time.

One-Leg Stand
The one-leg stand test involves standing on one leg, pointing the toes of your raised leg upward, and then looking towards the sky while performing a mental task, usually counting backwards from 30. The goal is to get you to mix physical and mental requirements, which most intoxicated brains struggle with. Sound difficult to do while sober? Try it. It is. For this reason, even when conducted properly, the study found that this test was only accurate 65 percent of the time.

Walk and Turn
This test involves walking a certain number of steps in a straight line in heel-to-toe fashion, as though you were walking on a balance beam. Once you have walked that number of steps, you then must turn without lifting your feet, and walk the same number of steps back. The goal is both to test balance and to see how well you can process instructions on the fly at the same time. The SCRI found that once standardized, this test was only accurate about 68 percent of the time.