Field Sobriety Tests and their Weaknesses

Field Sobriety Tests are tools used by police officer to build a DWI case against a person.  They are supposed to be used to determine the difference between a person who is sober, and a person who is impaired.  When properly administered they can be useful for this purpose, but they are not foolproof.  Much of the time, however, the tests are not properly administered.  This further reduces the reliability of the tests.  Let’s examine each of these tests and how they can cause problems for people who are not impaired.

The first test that is supposed to be administered is the Horizontal Gaze Nystagmous Test.  The officer tests the eye as it tracks a stimulus back and forth.  He or she is looking for involuntary shaking of the eye (also called nystagmus).  An officer is looking for six clues of an elevated BAC (three in each eye.)  While this is supposed to be the most accurate of the three tests, it is possible that the officer has either accidentally caused nystagmus or has misinterpreted nystagmous.

The second test that is supposed to be administered is the Walk and Turn.  The officer gives multiple instructions that a person has to follow.  This is a classic divided attention test.  This test has eight different clues that an officer must look for.  If an officer fails to instruct the test properly then it is possible that some of the clues may be caused by the officer’s failure to communicate the test instructions.  Of course, one of the main problems for Field Sobriety Tests is the fact that even when dead sober, some people would be unable to pass them because of physical or balance issues.

The test that is supposed to be administered third is the One Leg Stand test.  The officer has the person who is being tested stand one leg, and count out loud.  There are four clues that an officer is looking for.  Some of these clues can come from things other than impairment, such as poor balance, and nervousness.

Clearly, there are multiple reasons that people fail these tests.  While many times it is alcohol impairment that causes the failure, other times there are other reasons that come into play.  One factor that can cause poor performance on the Walk and Turn and the One Leg Stand is an accident.  People are often investigated for DWI after an accident, and it should be no surprise that they struggle with physical and mental tests, especially if they are physically injured or are in pain.  These other problems with the tests may be used as a defense.