Using a weighted mean to compute the values of simulator solution standards

The accuracy of breath alcohol measurements is determined by the measurement of known standards and requiring that the systematic error be less than some appropriate level (i.e., +/- 5%). This is typical of all analytical measurements. The measurement of known and traceable standards is the basis for determining accuracy and thereby confidence in all analytical results. The accuracy of breath alcohol instruments is typically determined through the use of simulator devices containing an aqueous ethanol solution. The results of simulator ethanol concentrations determined by gas chromatography were recently evaluated. The protocol had six different forensic toxicologists perform five measurements each on a particular batch of aqueous ethanol solution. The results were reported to three decimal places. Frequently, the individuals performed their set of measurements on different days. The reference value of the solution was then computed as the arithmetic mean of all 30 measurements and reported also to three decimal places.