A field sobriety test is used to determine if you're intoxicated. Not all tests are created equal, which is why it's vital that you pay attention to the test being given and the way in which it's given. If it is given incorrectly or produces a number of differing results, the test itself may not be admissible in court.
The Standardized Field Sobriety Test has been used since the 1970s. There are actually three tests performed during the SFST. The three tests include one-leg standing, walk-and-turn, and horizontal gaze nystagmus. The three tests combined help police officers determine if you are intoxicated, whether or not it's from alcohol.
Researchers have shown that this group of tests is accurate over 90 percent of the time when performed by alcohol-impaired drivers. Each test is normally performed well by sober drivers with few exceptions.
One of the things to keep in mind with these tests is that there can be reasons other than intoxication for failing. For instance, a person with poor balance may not be able to perform the walk-and-turn or one-leg stand tests. Someone with a head injury may take the HGN test and have it come back positive despite not being intoxicated. The HGN test may be failed by those using seizure medications, depressants or other types of drugs.
While these tests may be used in court, only the HGN results are based in science and easily challenged. Your attorney can help you fight HGN results that claim you were intoxicated by showing how the test was flawed and worked against you.
Source: DUI Justice Link, "Standardized Field Sobriety Test," accessed June 06, 2017