The standardized field sobriety tests used by most police agencies around the country were developed by researchers for the National Highway Traffic Safety Administration (NHTSA) as a way to give officers in the field a method for determining impairment at BACs of 0.1 or greater. Later "studies" were done to determine if the standardized battery of three tests were still reliable at BACs of .08.
Individually, the three standardized tests that are used around the US are not very reliable. The Horizontal Gaze Nystagmus (HGN) test, used to check a DUI suspect's eyes, has a reliability of 77%. The Walk and Turn test (9 steps on a straight line, turn and come back) only provides an accurate result only 68% of the time, and the One Leg Stand test is only accurate 65% of the time.
NHTSA has funded additional studies of the field sobriety tests since they were first developed. Three major studies all concluded that the combined results could achieve higher accuracy, one said as high as 95%, when "properly" administered. The trouble with these studies is that the techniques used for obtaining the data were not consistent with valid scientific and analytical methods. In short, the high reliability numbers established by these field sobriety testing studies are very misleading.
Many factors can impact the results officers obtain when they administer the test battery. Some of those factors include:
The officer is supposed to do what he can to minimize factors which could impact the reliability of the tests, but often they simply cannot do so for various reasons. In those circumstances, the officer should take the adverse conditions into account when he/she scores the results, but again, they most often do not do so.
Field sobriety tests have limited usefulness, but until the government gives officers a better alternative for in-the-field evaluation of DUI suspects, we will be stuck with these tests. In West Virginia, and in many other states (check your local laws) a driver may decline to perform the field tests because they are deemed to be voluntary. If your state permits you to refuse to perform these tests, absolutely do refuse them. They are not going to help you avoid an arrest and will just give the officer more evidence to use against you. The reality is that they are abnormal tests of abnormal physical skills and you will more than likely do poorly on them regardless of alcohol consumption.