Field sobriety tests have become so commonplace that most residents of New York expect that police officers will perform at least one on individuals they believe are driving under the influence. These tests are meant to determine whether or not an individual is intoxicated. However, it wasn't until the mid-1970's that the National Highway Traffic Safety Administration (NHTSA) decided to determine what field sobriety tests (if any at all) really might detect whether a person was driving while intoxicated (DWI).
Before 1975, field sobriety tests performed were up to the individual officer administrating them based on mere anecdotal experience. The NHTSA, in hopes of standardizing field sobriety tests so that it would be more simple to admit such tests into court, joined up with the Southern California Research Institute to test them.
Six field sobriety test were studied. However, only half of them were found to be somewhat effective on a regular basis for determining if a person was intoxicated. These field sobriety tests were the "One-leg Stand" test, the "Walk-and-Turn" test and the "Follow-the-Finger" test. These tests were each developed in order to identify different signs of intoxication.
However, even these field sobriety tests were initially not always effective in identifying whether or not a person was under the influence. The initial study found that the "Follow-the-Finger" test only saw a success rate of 77 percent, the "Walk-and-Turn" test only saw a success rate of 68 percent, and the "One-leg Stand" test only saw a success rate of 65 percent. Nevertheless, these became the standard field sobriety tests and were admitted in court as evidence of intoxication.
However, the initial studies were shored up by a number of other studies conducted during the 1990s. In these studies actual officers administered the three standard field sobriety tests, rather than researchers. The 1990s tests combined with the initial tests determined that the three standard field sobriety tests were more than 90 percent accurate in identifying intoxicated individuals. Nevertheless, non-standardized field sobriety tests are still used by some, even though their effectiveness has not been studied or determined.
As this shows, field sobriety tests may not always be effective. In addition, they may be especially prone to the subjectiveness of the officer performing them. Therefore, it is important to challenge the accuracy of such tests in one's defense.
Source: Atlas Obscura, "The Sober Truth About Field Sobriety Tests," Eric Grundhauser, Feb. 18, 2016