Field Sobriety Tests: How Accurate are They?

Field sobriety tests are used to establish probable cause in arrests for drunk driving. What many don’t know is that these tests are highly unreliable determiners of blood alcohol content (BAC). In the late 1970s, the National Highway Traffic Safety Administration (NHTSA) charged the Southern California Research Institute (SCRI) with choosing the most accurate field sobriety tests out of the many tests used at the time. After conducting a study, the SCRI determined that the one-leg stand test, the walk and turn test, and the horizontal gaze nystagmus test were the most accurate.

Error Rates in Field Sobriety Tests

Unfortunately, the studies conducted in the 1970s were not without their fair share of marginal error as well. The SCRI studied only 10 officers as they used different tests to determine whether participants had a BAC of .10% or higher. After this study, the NHTSA knew that the officer error rate was 47%. In an effort to curb this margin of error, they hired the SCRI to standardize field test administration.

Standardizing the tests had the following effect:

  • Horizontal Gaze Nystagmus: 77% rate of accuracy
  • Walk and Turn: 68% rate of accuracy
  • One-Leg Stand: 65% rate of accuracy

When all three tests were used together, the officers were correct 82% of the time. This still leaves a considerable margin of error for those who are taking the test. In addition, even when these tests are correct, they do not indicate the individual’s ability to drive a car and are not a scientifically proven foundation for pressing charges.

If you or a loved one are facing OWI charges, get in touch with a trusted Fort Wayne OWI attorney from Arnold Terrill Ridenour, P.C. We share more than five decades of experience and are passionate about defending our clients’ rights.

Learn more about your legal options by contacting us today.