Law enforcement may use a wide range of field sobriety tests. However, the National Highway Traffic Safety Administration only approves three: the one-leg stand test, the walk-and-turn test and the horizontal gaze nystagmus test. These three form a battery referred to collectively as the Standardized Field Sobriety Test.
Authorities need not confine themselves to the SFST and may use nonstandard field sobriety tests. However, the results of such assessments may not be admissible in court. Additionally, certain factors may also affect the admissibility and/or accuracy of one or more components of the SFST.
Accuracy
Validation testing of the Standardized Field Sobriety Testing approximately 20 years ago affirmed a high rate of accuracy in correctly identifying impairment when authorities administered the three assessments together. Individually, however, the accuracy of each was significantly lower.
Furthermore, even if you have not been drinking, you may have an underlying medical condition or disability that could affect your ability to successfully perform sobriety testing. For example, a neurological condition that affects balance or causes vertigo could affect your ability to perform the one-leg stand test and/or the walk-and-turn test. An eye disease could affect your horizontal gaze nystagmus results. If you have a disability or condition that may affect your ability to perform field sobriety tests, you should inform law enforcement.
Admissibility
Results of field sobriety tests not included in the SFST may not be admissible in court. In 2017, the Georgia Supreme Court ruled that a nonstandard field sobriety test, the Romberg test, was not admissible because it was not scientifically verifiable.
Among the assessments included in the SFST, the standard for the horizontal gaze nystagmus test is higher than the standard for the other two. Due to its scientific nature, authorities must perform it according to established protocols or risk having it challenged. To express an opinion about the results in court, a law enforcement officer must qualify as an expert witness.
However, standards are less strict for the other two components of the SFST battery. Suppressing results of the walk-and-turn and one-leg stand tests cannot take place due to deviations from the established procedure during the administration of each.