Validation of the Standardized Field Sobriety Test Battery at BACs below 0.10 Percent

Stuster, Jack 1947-; Burns, Marcelline; States), Anacapa Sciences (United · 2007 · OpenAlex-citations

DOI: 10.21949/1525409

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Summary

This study, conducted by Anacapa Sciences, Inc. for the National Highway Traffic Safety Administration (NHTSA), evaluated the accuracy of the Standardized Field Sobriety Test (SFST) Battery in discriminating blood alcohol concentrations (BACs) below the previously validated threshold of 0.10 percent. The research was motivated by a legislative trend to lower statutory Driving While Impaired (DWI) limits to 0.08 percent BAC. The primary objective was to determine if the SFST battery, originally validated in 1981 for 0.10 percent BAC, could reliably assist law enforcement officers in making arrest decisions at the lower 0.08 percent and 0.04 percent thresholds. The study employed a field validation design in San Diego, California. Seven officers from the San Diego Police Department’s alcohol enforcement unit, who possessed prior NHTSA-approved SFST training, participated in the research. These officers received refresher training on modified scoring procedures: observing four Horizontal Gaze Nystagmus (HGN) clues indicated a BAC ≥0.08 percent (previously ≥0.10 percent), and two HGN clues indicated a BAC ≥0.04 percent. During routine patrols, officers administered the three-component SFST battery (HGN, Walk and Turn, and One Leg Stand) and completed data collection forms for each test. The final step in each case was the administration of an evidentiary breath alcohol test to establish the actual BAC. Data analysis included 297 motorists after excluding one refusal case. The results demonstrated that the SFSTs were extremely accurate in discriminating between BACs above and below 0.08 percent. The mean estimated BAC (0.117) and measured BAC (0.122) differed by only 0.005 percent, a difference deemed operationally irrelevant. Correlation analyses identified the HGN test as the most predictive individual component (r=0.65), though combining all three tests yielded a higher correlation (r=0.69). Decision analyses revealed that officers’ estimates of whether a motorist’s BAC was above or below 0.08 percent were accurate in 91 percent of cases, rising to 94 percent when explanations for false positives were considered. For the 0.04 percent threshold, officers’ estimates were accurate in 94 percent of arrest decisions and 80 percent of cases overall. Additionally, interviews with officers and prosecutors confirmed the test battery’s acceptability for establishing probable cause for DWI arrests. The study concludes that the SFST Battery is valid for discriminating BACs at the 0.08 percent level using slightly modified scoring procedures. Furthermore, the findings strongly suggest that the tests also accurately discriminate at the 0.04 percent BAC level. These results provide scientific support for law enforcement agencies adopting lower BAC limits, confirming that standardized field sobriety tests remain reliable tools for detecting impairment and supporting arrest decisions at these reduced thresholds.

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• dui enforcement

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• Methodological Resource: validation psychometrics