Precision, accuracy and relevance of breath alcohol measurements

The methods employed for evaluating the performance of some currently available breath alcohol devices are described. A program consisting of in vitro experiments, extensive in vivo laboratory studies, controlled field studies, and finally roadside random testing has been used. The importance of considering the underlying physiological mechanisms particularly with regard to the blood/breath partition ratio and its variability is emphasized. An important finding is that the relationship varies with the phase of alcohol metabolism in a regular and systematic way. Some statistical techniques are outlined for calculating the precision and accuracy of breath-testing instruments, which are important properties of a method to be used for medico-legal purposes.