Factors contributing to the variability observed in duplicate forensic breath alcohol measurement

Abstract

Several factors contribute to the variability observed among repeated measurements of breath alcohol concentration. Identifying these factors and the magnitude of their contribution is the focus of this study. Large breath alcohol data sets consisting of duplicate test results from drivers arrested for driving while intoxicated were obtained from four jurisdictions: Sweden, Alabama, New Jersey and Washington State. The absolute difference between duplicate results were fitted to a multivariate linear regression model which included the following predictor variables: mean breath alcohol concentration, absolute exhalation time difference between repeated measurements, absolute exhalation volume difference, gender and age. In all data sets considered here, the breath alcohol concentration was the most statistically and practically significant predictor of absolute difference between the duplicate results. The next two most important predictors to enter models for all jurisdictions were exhalation volume difference and exhalation time difference. The maximum multivariate R² for any jurisdiction, however, was only 0.24, suggesting that other factors not considered here may be of importance. Two predictors over which the subject would have some influence included exhalation time and volume. When these were set at values expected to have maximum impact, the effect on duplicate test differences was very small, 0.008 g/210 L or less in all jurisdictions, indicating that subject manipulation of exhalation time and volume would have at most a very small systematic effect on estimated breath alcohol concentration. This study presents multivariate models useful for identifying the impact of five variables that may influence breath test variability.

Biomolecules and Biomarkers Used in Diagnosis of Alcohol Drinking and in Monitoring Therapeutic Interventions

“…Variability exists in replicate breath alcohol exhalation profiles for one subject collected over a short time interval. There were no age or gender influences, while the breath exhalation volume and breath exhalation time also lacked significant associations [ 63 ]. However, the breathing pattern seems to have an effect.…”

The Variability of the Blood/Breath Ratio and Its Impact on the Results of Breath-Alcohol Analyses: A Rejoinder

“…The quality assurance is important in conjunction with evidential breath alcohol testing considering that the results are used in a criminal prosecution as reviewed in detail elsewhere . For example, a suspect should be kept under observation for at least 15–20 min before a breath test to avoid claims that “mouth-alcohol” influenced the results. , Two separate exhalations should be analyzed from each suspect about 3–5 min apart, and a good agreement between the duplicate measurements represents an independent confirmatory test result. − Accuracy of the breath-alcohol instrument is verified each time a suspect is tested by the analysis of known strength air-alcohol vapor standards generated using a wet-bath simulator or via compressed dry-gas standards traceable to some primary source. , …”

In vitro evaluation of BACtrack®'s smartphone-connected personal breath alcohol analyzers

“…For in vivo use, manufacturers of these devices should consider programing the instrument for a duplicate breath test sequence, reporting the mean of the two measurements along with the associated uncertainty. An uncertainty function could be built into the software of the smartphone app to provide users with additional information about the uncertainty of the measurements obtained (48). Also, calibration reports could be recorded by the smartphone app and notify the user when recalibration is needed.…”