Citation

Wigmore JG, House CJ, Langille RM. J. Can. Soc. Forensic Sci. 2005; 38(1): 1-8.

Copyright

(Copyright © 2005, Canadian Society of Forensic Science, Publisher Informa - Taylor and Francis Group)

DOI

10.1080/00085030.2005.10757580

PMID

unavailable

Abstract

A one-year retrospective study was conducted of 2,759 duplicate Intoxilyzer® 5000C test results in the City of Toronto during 1995 with a statutory wait of "at least fifteen minutes" between tests. The time between tests ranged from 19 to 73 minutes (median = 22 minutes). The absolute difference between the first and second breath tests ranged from 0 to 0.042 g/210 L (median 0.007 g/210 L). The distribution of these differences was not normal (KS = 0.1566, skewness = −0.1143). The differences between the truncated first and second tests were not within the recommended 0.02 g/210 L in 7.5% of the paired data. The second test was ≥ 0.01 g/210 L less than the first breath test in 35% of the cases (n=981) but was ≥ 0.01 g/210 L greater than the first breath test in only 7% (n=203) using truncated results. The observed skewness in this distribution is likely due to the elimination of alcohol that occurred during the time between tests. Following the adjustment of the second test to account for the mean pharmacokinetic alcohol elimination rate in drinking drivers, the distribution represented by the difference between the two tests still represented a non-normal distribution (KS = 0.3787) but was less skewed (skewness = −0.0549). The differences between the first and second tests following this pharmacokinetic correction resulted in reduction in the number of tests outside the recommended 0.02 g/210 L difference to 1.6%. It is recommended that the statutory wait of "at least fifteen minutes" in the Criminal Code be changed to a time period of between at least two minutes to five minutes, to reduce the variability between the two test results.