A Statistical Evaluation of Calibration Check Intervals

In 2009 the Alcohol Test Committee of the Canadian Society of Forensic Science changed the calibration check interval of Approved Screening Devices from every 2 weeks to every 31 days. Data from 612 calibration checks of a group of Alco-Sensor IV DWF screening devices were analyzed using a contingency table and analysis as well as a significance test for a difference in proportions. There were no statistically significant differences between the length of time of the calibration interval and the frequency of a device requiring recalibration. This analysis shows the Alco-Sensor IV DWF is no more likely to require calibration up to and including a 5 week interval when compared to a 2 week interval, supporting the Alcohol Test Committee decision.