Reproducibility of Within-Subject Breath Alcohol Analysis

Abstract

Random samples from normal distributions are an important assumption for many statistical methods. The present study evaluates this assumption with regard to quantitative breath alcohol analyses. Eight individuals (six male and two female) consumed alcoholic beverages and subsequently provided replicate (n ranging from 22 to 69) breath samples to an infrared breath alcohol instrument within short time intervals. The serially collected data were treated with several descriptive and inferential methods. Descriptive results among the eight individuals included: mean 0.0420–0.1175 g/210L, SD 0.0008–0.0045 g/210L and CV: 1.9%–4.7%. Statistical tests for normality showed seven of the distributions to be reasonably normal (p ≥ 0.25) and the other marginal (p = 0.051). A test for runs about the median showed random results (p ≥ 0.10) for four individuals and non-random (p ≤ 0.01) for the other four. The results suggest an individual's breath alcohol measurement, when appropriately collected and analysed, should be considered a random sample from a normal within-subject distribution. The existing variability in breath alcohol analysis, due largely to biological and sampling considerations, is acceptably minimized to warrant forensic application.