Brady Melton

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  Student Presentation: Evaluating the Strength of Evidence in DWI Cases Presented in North Carolina
  Rebecca Law, Brady Melton

  Criminal penalties for driving while intoxicated (DWI) in North Carolina are based on hard thresholds; for example, having a blood alcohol content (BAC) at or above 0.08 is considered legally impaired. However, BAC measurements are typically taken using breathalyzers, which are subject to measurement error. Additionally, breathalyzer readings in North Carolina are truncated, i.e. a person blowing a 0.079 would have a breathalyzer reading of 0.07. The purpose of our research is to explore this error and to construct recommendations for both law enforcement and courtroom decisions. Using data collected from breathalyzer tickets in Orange County, we have estimated the measurement error using a truncated random effects model and have calculated a prediction interval to determine any individual’s true BAC given the individual’s breathalyzer results. We also ran a parallelized simulation study to determine the effects of the distribution parameters on our model, and plan on exploring factors such as temperature, humidity, and machine calibration. We have created two lookup tables to determine an individuals true BAC, one based on prediction intervals, and the other on the probability that an individual’s true BAC is above 0.08. Using these lookup tables, the courts can determine the strength of evidence in DWI cases.