Field sobriety tests are given to establish probable cause that an individual is impaired by alcohol and/or drugs. At some point, courts started to allow field sobriety tests and their results as proof that a person is under the influence. Since as far back as 1984, all police academies in Missouri train law enforcement officers field sobriety testing according to the National Highway Traffic Safety Administration. These tests were developed by Tharp, Burns & Maskowitz; at the University of California, Berkeley.
The three field sobriety tests tested by the NHTSA are horizontal gaze nystagmus (HGN), walk and turn, and one-leg stand tests. NHTSA promulgates very specific guidelines for how these tests are to be conducted and the officers are trained to perform the tests that way. However, NHTSA’s own studies show the error rates (even with highly trained officers) in these tests range from 17% to 35%. As it is stated in NHTSA’s own training manual, if the officer makes errors, or changes in the administration of these tests, then the accuracy of the tests is obviously compromised.
