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An all too common misconception, and also the main cause of erroneous blood-alcohol readings, is that the person being tested is average in all of the physiological qualities which affect the results of the test. Acquiring a precise level of alcohol content in the blood is determined based entirely on a list of certain scientific assumptions. More often than not, these assumptions are false, producing inaccurate readings of the individual’s blood sample. An individual tested is seldom “average” in any one of the biological traits assumed to be typical of an individual. One false assumption is regarding the relation between alcohol in the breath and in the blood such that the ratio in an “average” individual is 1:2100. All breath testing machines use this ratio when analyzing and comparing the results of breath and blood samples. In essence, the accuracy of the results obtained depends upon the accuracy of the original supposition. In reality, the blood-to-breath ratio can range anywhere from 1:1300 to 1:3000. Consequently, an individual with a ratio of 1:1700 and a real blood-alcohol level of .08 would produce a reading of .10 with a “precise” breath testing machine. In other words, the breath testing devices merely test a set of qualities found in an “average” person but use the individual’s breath and blood samples to do so. Another instance of an incorrect assumption about the “average” subject is with respect to urinalysis. It is supposed that on average, the bladder contains 1.3 parts alcohol for every 1 part alcohol found in the blood. In truth, the actual proportion differs considerably from person to person. Again, if the assumption is incorrect, the blood-alcohol reading from the urine will also be false. Retrograde extrapolation is a term used for the assumption that alcohol levels in the blood decline after the subject stops drinking; a theory often unfairly exploited as evidence by the prosecutor. Because the blood-alcohol amount when the test was taken is not directly related to the charges, the state will attempt to predict the percentage when the person was driving. The usual technique to determine the blood-alcohol level while driving estimates how much alcohol was “burned off” between the times of driving and testing. In order to do this, the calculation relies on two more assumptions:
Even if one could concede that the defendant’s blood-alcohol level was decreasing, it is truly impossible for the prosecution to know the exact burn-off rate of the subject. What if the “burn-off” for this particular individual is .005 percent? Or .3 percent? Like the others, this assumption is based on an “average” and not on the particular individual. And like the other situations, inaccuracy of the assumption correlates to inaccuracy in the extrapolation. The fallacy of “average” extends further than chemical analysis; it is also found with the officer in the field. One of the popular field sobriety tests, the “horizontal gaze nystagmus”, is also based on “Mr. Average.” The officer is coached to be able to determine the angle at which the subject’s eyes begin jerking. By subtracting the angle from 50, an officer can supposedly make a blood-alcohol reading. Then jerking at 35 degrees would yield a reading of .15 percent blood-alcohol level. It is unclear how the number 50 was designated for this obviously unscientific measure of a person’s level of alcohol intoxication? Let’s assume for the sake of playing devil’s advocate that the method has validity, when subtracting the individual’s eye jerking angle, who does the default angle of 50 degrees apply to? The answer, once again, is the “average” individual. Presumably, an average person’s eyes would begin jerking at 40-45 degrees if he or she has .10 or .05 percent blood-alcohol content. Another way officers perform the horizontal gaze nystagmus test is by failing the individual if their eyes jerk before 40 or 45 degrees. Clearly, such test results are subjective. Ironically, with both situations, the “baseline” is unknown. A baseline is the angle that the eyes would begin jerking when sober. The person is expected to be perfectly identical to the “average” individual. An individual with a .07 percent blood-alcohol level could be impaired when another person at .10 percent is not. This is a perfect example of how tolerance can differ between people. Surprisingly, however, individual tolerance to the impact of alcohol is not taken into account. The Way Breathalyzers Work California DUIs and DWIs Blood-Alcohol Tests The Definition of Breath-Alcohol Testing |
Copyright 2001 - 2008 |
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Los Angeles DUI Laws and Lawyers offers information for individuals who have been accused with drunk driving. It is also here to oppose the organizations striving for use of unjust evidence/procedures, harsh laws, a return of the prohibition, and the persistent obliteration of our constitutional rights. The National Motorists Association provides a site where similar topics are discussed, such as DUI checkpoints, license revocations/suspensions wrongfully enforced by officers in the field, and unjust criminal penalties. |
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