The 131st Annual Meeting (November 15-19, 2003) of APHA

Abstract #68413

Melissa A. Schiff, MD, MPH and Peter Cummings, MD, MPH. Harborview Injury Prevention and Research Center, University of Washington, 325 Ninth Ave, Box 359960, Seattle, WA 98104, 206-521-1527, mschiff@u.washington.edu

Purpose: To evaluate agreement between police and trained investigators regarding seat belt use by crash victims, according to injury severity. Methods: We used data from the National Accident Sampling System Crashworthiness Data System (CDS) for front seat occupants, 16 years and older, in crashes during 1993-2000. CDS investigators determined belt use from vehicle inspection, interviews, and medical record information; their assessment was considered the gold standard for this analysis. Occupant severity of injury was categorized in five levels from no injuries to death. We estimated the sensitivity, specificity, and area under receiver operating characteristic curves (AUC) for police reports of belt use. Results: Among 48,858 occupants, sensitivity of a police report that a belt was used was 95.8% overall and varied only modestly by injury severity. Specificity of a police report that a belt was not used was 68.9% overall; it was lowest among the uninjured (53.2%) and greatest among the dead (90.0%). The AUC was 0.82 (95% CI 0.82 to 0.83) overall; this was lowest among those not injured (0.75, 95% CI 0.74 to 0.76) and increased with injury severity to 0.91 (95% CI 0.91 to 0.92) among those who died. Conclusion: Police usually classify belted crash victims as belted, regardless of injury severity. But they often classify unbelted survivors as belted when they were not. This misclassification may result in exaggerated estimates of seat belt effectiveness in some studies.

Learning Objectives:

• 1. Describe how sensitivity and specificity of police reports compared to CDS investigators reports of seat belt use vary with injury severity.
• 2. Describe how the area under the curve varies with injury severity.
• 3. Recognize that use of police assessments of seat belt use may result in biased estimates of the effectiveness of seat belts on preventing injury and death.

Keywords: Motor Vehicles, Methodology

Presenting author's disclosure statement:
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.