In our last post, we raised the question of the evidentiary value of field sobriety testing. This is an important issue for a couple of reasons.

Firstly, field sobriety testing is typically used by police officers as a means of gathering enough evidence to support probable cause to make an arrest, upon which occurrence an officer would then be able to administer an official breath test to determine the suspect’s level of intoxication more precisely. The latter test typically has strong evidentiary value, unless there are problems with the conditions and circumstances under which it was administered.

Secondly, field sobriety testing may have evidentiary value in court—either by itself or in conjunction with other evidence—and so may be used by prosecutors as evidence supporting a conviction. The issue with field sobriety testing is that some of the tests that officers sometimes use do not have strong evidentiary value. There are several individual tests, collectively known as the Standard Field Sobriety Test (SFST), which may have evidentiary value in court, provided they are performed correctly.

The three individual tests are the horizontal gaze nystagmus (HGN), the one-leg stand, and the walk-and-turn. According to AAA, research shows that the Standard Field Sobriety Test is able to correctly identify intoxicated drivers over 90 percent of the time. This means that while these tests are fairly accurate, they are not infallible.

In our next post, we’ll look at some of the potential reasons for the infallibility of these tests and offer some comments on how an attorney can help mount a strong defense in drunk-driving cases involving evidence of field sobriety testing.

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