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The root cause for inaccuracies in blood-alcohol testing is the mistaken belief that the people being tested all have “average” physiological attributes. In other words, the accuracy of every blood-alcohol test result is contingent upon the validity of a set of specific assumptions. To the detriment of the individual being tested, the assumptions are hardly ever correct. The likelihood that the individual being tested has “average” attributes is extremely low. All breath testing machines assume that the proportion between alcohol in the breath and alcohol in the blood is 1: 2100. The BAC machine is configured to base its reading entirely on this assumption. In actuality, these proportions in an individual can differ from anywhere between 1:1300 to 1:3000 or more. Doing the math, a person who had a 1:1700 breath-to-blood ratio and a genuine blood-alcohol level of .08% would actually get a reading of .10%. This would be an “accurate” reading from a breath testing machine that compared the results with the “normal” ratio. The validity of the readings corresponds directly to the validity of the original assumption. In reality, these machines repeatedly assess an average person, only using a defendant’s breath sample. There is no regard to the defendant’s physiological individuality. Urinalysis is another excellent example of these assumptions. “Normal” means there are 1.3 parts alcohol in the bladder’s urine when there is 1 part alcohol in the blood. When a subject’s urine is tested for blood-alcohol, the real ratio can differ from person to person. Because the ratio is inaccurate, the results of the blood-alcohol test will also be inaccurate. Retrograde extrapolation is yet another example of this dependency on the idea that the defendant will be “average”. This term basically means guessing backwards. Usually the test is administered well after the incident so the state attempts to make an educated guess on the level of alcohol in the blood while the defendant was driving, which is the most pertinent information to the case. The prosecution calculates this number based on two assumptions:
Supposing that the level of alcohol was decreasing, how can the prosecution be sure of the exact rate? Perhaps the alcohol was “burning off” at .005 percent? Or even at .2 percent! It is evident that there is no concrete scientific way for the prosecution to know this detail. The method of calculation assumes the elimination rate is the “average” rate. Again, inaccuracies in the assumption mean inaccuracies in the extrapolation. The ever-present assumption about the “average” does not stop with chemical analysis. It can be found with the officers in the field as well. The most frequently used field sobriety test is the “horizontal gaze nystagmus” that requires the officer to determine the angle at which the suspect’s eyes begin to jerk. The officers have been trained to perform this test, however, the readings still depend on the “normal” numbers as the baseline. A blood-alcohol reading can, hypothetically, be deduced by subtracting the angle at which the suspect’s eye begins jerking from 50. For example, if the eyes begin jerking at 35 degrees, the level of alcohol in the blood would be .15 percent. Where does the number 50 originate, though? “Mr. Average.” Another technique of conducting the horizontal gaze nystagmus would be to fail the individuals if their eyes begin jerking before 40 or 45 degrees. The reason for this is because, in theory, they would have a blood-alcohol level of .10 or .05 percent. An important fact to note, in both methods of administering the test is that the “baseline” is unknown. (The baseline being the angle that the individual’s eyes would jerk when sober.) Once again, the subject is expected to be physiologically the same as the “average” individual. Blood-Alcohol Tests DUIs in California Breathalyzers: How They Work The Encyclopedia Definition of Breath-Alcohol Testing |
Copyright 2001 - 2008 |
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Orange County DUI, first and foremost, is a resource for individuals who have been charged with driving while intoxicated. It is also a source to oppose individuals and organizations who support severe laws, unjustifiable procedures, breach of our rights as citizens, and the return of prohibition. More information on related topics, such as unsuitable criminal penalties, unconstitutional roadblocks, and immediate license suspensions and revocations, can be found at the National Motorists Association’s homepage. |
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