Monday, August 26, 2013

How Accurate are Field Sobriety Tests???

Posted by Attorney Greg Simms, 502.618.4949

You would think that would be an easy question to answer, but it isn't.

The Standardized Field Sobriety Tests (sometimes referred to as "SFSTs" or "FSTs") that are the staples of Law Enforcement sobriety testing today, include the Horizontal Gaze Nystagmus (HGN), the Walk and Turn (W&T) and the One Leg Stand (OLS) tests.

The tests were conceived by the Southern California Research Institute (SCRI) around about 1975.  I presume these people were academics, and not actual doctors.  And for the purpose of this blog we will assume that they were not funded by an agency or company with any outside interests - that the people at the SCRI were genuinely unbiased.

The HGN is the test where a police officer puts a finger in front of your face, and moves it around.  They tell you to follow their finger with your eyes, and the officer looks for involuntary jerking of the eyes, called "nystagmus."  This word is pronounced most commonly as "nis-TAG-muss" and less commonly as "na-STY-muss."

The walk and turn test and one leg stand tests are pretty self explanatory.  If you can't figure them out, raise your hand and Tommy will come along and hit you in the head with a tack hammer...

Anyway, when the SCRI developed the tests in 1975, they gave a percentage of accuracy for each test in determining the impairment of a subject test taker.  Those percentages are as follows:

-The HGN alone, was 77% accurate
-The W&T alone, was 68% accurate
-The OLS alone, was 65% accurate

and the combination of the HGN and W&T yielded an accuracy of 80%.  If you have any questions about math, feel free to text my friend, Jeremie Wade.  He loves that.

These " percentages of accuracy" are legitimate if, and only if, the tests are performed correctly by the police officer, and only if the test results are interpreted correctly by the police officer.

Let me expound on that just a little bit.  There are a lot of details involved in giving these tests.  Specificities that the officer has to remember.  For example, when performing the HGN test, the officer's finger should be between 12-15 inches in front of the subject's face.  A lot of officers have forgotten this information years after learning it, and some don't remember the numbers correctly (for some reason a lot of officers think it's 12-18 inches.  

In addition, and maybe more importantly, the guidelines for the tests state specifically that the officer is always supposed to turn the subject test taker AWAY from any flashing lights (like the cruiser's emergency lights).  This makes sense because the officer is looking for "jumping" in the eyes, and flashing lights can cause your eyes to jump, or jerk.  Surprisingly, I have found that an extremely high percentage of police officers do NOT turn subjects away from the flashing lights - like 50% or so.

The problem with doing the tests wrong, is that - obviously - you can get bad results.  Even the guidelines state specifically that "if any one of the standardized field sobriety test elements are changed, the validity is compromised."  The book seems to think that's pretty important, because in the book, that writing is in all caps, and bold letters.

There are a LOT more details associated with performing the HGN test - like the seconds it takes to do a full sweep, the method for determining the onset of nystagmus prior to 45 degrees, and the specific time of the hold at maximum deviation.  And we haven't even started on the W&T and OLS, which are also frequently performed incorrectly.

So the answer to the original question is - we kind of don't know.  We know how accurate the SCRI says the tests are supposed to be if they are done correctly.  But we also know that a lot of police officers don't do them correctly - and that the guidelines say that compromises the validity of the tests.

So... my bad.  I hate to give you a question like that, and then not answer the question.  That must be frustrating for you.  If it makes you feel better, I empathize with you.

If you have any more questions on field sobriety tests, let me know.  Feel free to contact me, Greg Simms, at 502.618.4949.  Or drop by.  My door is always open.

Questions Answered in this Blog Post:  How accurate are Field Sobriety Tests FSTs SFSTs; what is the accuracy rate of HGN W&T OLS; accuracy for Horizontal Gaze Nystagmus, Walk & Turn and One Leg Stand tests; how can I find a good DUI lawyer in Louisville Kentucky; DUI lawyers for Elizabethtown Kentucky; Hokum Field Sobriety tests?

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