Estimating Uncertainty in Wisconsin's Evidential Breath Alcohol Measurements

Breath alcohol measurement accuracy and precision quantification is a critical component of impaired driving prosecution and is required for laboratory accreditation. The Chemical Testing Section of Wisconsin's Department of Transportation conducted a bottom-up study to quantify uncertainty of breath alcohol measurements conducted on Intoximeter's EC/IR II instrument. After an exercise in combined uncertainty source identification, individual input values were either reported from National Institute of Standards and Technology traceable reference materials or quantified using instrument data from 2014 to 2018. From input values, an expanded uncertainty value of 4.58 × 10-3 g/210L was found that encompasses all identified sources with a 95% confidence interval.