Supposing for whatever reason, a cop asks a person who knows themselves with certainty to be completely sober (e.g. they have no consumed any alcohol in days) to take a field sobriety test? (Maybe the car was weaving a bit, or perhaps the cop is just a jerk or idiot.) Should they agree or just insist on a breathalizer instead?
The reason I ask is I’ve been watching some FST in action (on YouTube) and ISTM that they are highly subjective and very difficult to “pass” to the point of convincing someone who is otherwise inclined to think you’re intoxicated. In particular, the one involving walking in a straight line one foot in front of the other (aka the “walk-and-turn test”). I’ve seen a couple of instances where I thought the person did a fairly decent job but the cop thought otherwise and snapped some handcuffs on them.
I’ve never actually been given a FST of any sort IRL, but my wife and I did this test at home a few times. It was frankly not easy to do it without wobbling at all or stepping out of line. And we are both in pretty good shape; I can only imagine people who are overweight or otherwise out-of-shape, who are older, tired, or just stiff from driving a while. So I think there’s a huge potential for the officer to just incorrectly assume that a sober person is intoxicated, whether due to innocent error, incompetance, or because he’s possibly in a bad mood and out to get you. Meanwhile, the BrAC and BAC tests are not completely error free, but are at least objective and much more reliable than the FSTs.
Of course, the above is assuming you’re actually confident that you’re not at all intoxicated and are not just making some possibly incorrect assumption about how much you drank and whether it wore off by now.
Also, I’m assuming that the FSTs are not obligatory without consent (see Wiki link below).
Looking at Wikipedia, I see there are critics of this test in particular.
Field sobriety testing - Wikipedia
Critics of standardized field sobriety tests often question the statistical evidence behind them, and the ability of the officers to administer the tests and actually judge for impairments related to alcohol. According to Barone, one study involved completely sober individuals who were asked to perform the standardized field sobriety tests, and their performances were videotaped. “After viewing the 21 videos of sober individuals taking the standardized field tests, the police officers believed that forty-six percent of the individuals had ‘too much to drink’”. The NHTSA’s 1977 study had an error rate of 47 percent, and the 1981 study had an error rate of 32 percent, which is considered unusually high for a scientific study.
One of the main criticisms of field sobriety tests is that the judgment is left up to the discretion of the police officer. An officer may have some bias towards a suspect and judge the test more critically than necessary. Additionally, it is almost impossible to tell whether or not a police officer used proper procedures for administering the field sobriety test when a case is brought to court. The original research conducted by the NHTSA is often disputed because of the manner in which they were conducted and the conclusions that were reported.
One author alleges that FSD analysis reports do not meet scientific peer review standards: “The reports for all three studies issued by NHTSA are lacking much of the material and analysis expected in a scientific paper, and none have been published in peer-reviewed journals” (Rubenzer 2008; Rubenzer 2011).
As noted above, these tests can be problematic for people with non-obvious disabilities affecting proprioception, such as Ehlers-Danlos syndrome (EDS). Conditions affecting mobility, physical ailments and age adversely affect performance on FSTs.
Is there any downside to this approach?