Myth #14: Breath Test —Truncating To Two Digits Favors The Defendant
In many, if not most jurisdictions, two readings are taken and the lowest three-digit reading is truncated, leaving two digits as the reported reading. The government argues this favors the defendant and removes uncertainty in the test reading. Dr. Dubowski argues the third digit is irrelevant because the instrument is not capable of accurately reporting to three digits.
Defending against DUI / DWIFigure 8 illustrates the uniform distribution of the third digits of field BrACs in g/210L. Gullberg also reported an essentially uniform distribution of third digits in field forensic breath alcohol testing. In truncating to two digits from three digits, the omitted third digits follow a uniform distribution. Third digits are discrete random variables with an equal probability of being 0, 1_.9. An unknown third digit is as likely to be 9 as 0. Truncating BrAC measurements in g/210L to two decimal places does not introduce bias other than the intended deletion of the third digit. Dr. Jones takes a different approach, noting that truncating unevenly favors those who have a higher third digit. Effective DUI / DWI DefenseIn some jurisdictions rules and regulations for evidential breath-alcohol testing mandate that the lowest of the two independent breath-tests is used for prosecution. Also the third decimal is frequently truncated so that 0.109 g/210 L becomes 0.10 g/210 L. However, these safeguards do not help the person who by chance might have the same BrAC result in the two independent breath-tests or when the third decimal might have been zero. Next article: Index: |
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