August 5th, 2006 Allen Trapp Posted in Field Sobriety Tests 2 Comments »
August 5th, 2006 Allen Trapp Posted in Field Sobriety Tests No Comments »
Tharps Equation is used in the DRE (drug recognition expert) protocol to determine whether or not alcohol is the cause of the observed nystagmus. In another words, it “rules” out alcohol as the cause of impairment. The formula the DRE candidate is taught is BAC = 50 - A (Angle of Onset).
The interesting thing about Tharps Equation is that it is merely a statistical approximation - not a mathematical formula (and we all know what Mark Twain says about statistics). Tharps Equation can be off by .05% or more, even if the person has consumed no drug other than alcohol. Even its proponents concede that Tharp’s Equation does not reflect an exact relationship for all subjects at all times (according to NHTSA).
Keep in mind that the SFST protocol only allows for the prediction of above or below the per se level. What usually happens is the DRE talks and unqualified officers use the formula to estimate the BAC (although 99% of the time they are not performing the Onset of Nystagmus Prior to 45 Degrees properly). We question the “reliability” of a statistical formula, as well as the proper estimation of 45 degrees by the Officer.
May 23rd, 2006 Rob Leonard Posted in Field Sobriety Tests 1 Comment »
Before you go any further, you need to read the NHTSA validation studies which can be found here, here and here. You also need to read the Cole and Nowaczyk study from Clemson University which was published in a journal called Perceptual and Motor Skills in 1994.
Having been trained in DUI detection and Standardized Field Sobriety Testing I have some thoughts on the subject. Mostly the tests seem to be very subjective and are poor indicators of impairment when someone has low and mid-range levels of alcohol in their system. I recently performed the tests on my mother-in-law, sister-in-law and my wife. Using the NHTSA scoring, the only one not going to jail is my wife. They were sober, indoors with no environmental difficulties commonly found on the side of the road and had no fear of being arrested. I swear I didn’t just decide to arrest my mother-in-law for no reason, she really did fail. She was not drunk, she just can’t do a divided attention test or follow directions.
So, how have these tests become so popular and widely accepted in court?  Society wants to convict drunk drivers. In the 1970’s, NHTSA paid a research group to come up with some tests. Many tests were tried and almost none were any better than a coin flip at determining whether someone was impaired or not. The three that did come up over that 50% that NHTSA adopted are the three test battery that we are all familar with. HGN, Walk & Turn and One Leg Stand. 70-80% accuracy is good enough for government work, so there you have it.
There are some more recent validations studies too that make the numbers even better according to NHTSA. The same lady (Burns) that originally proposed and validated the tests was behind the new validation numbers as well. It’s like asking Ford Motor Company, “Which American company produces the best cars?â€Â You knew what the answer was going to be before you even asked the question.
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