COMPARISON OF TWO METHODS FOR DEBIASING BEFORE-AND-AFTER ACCIDENT STUDIES (DISCUSSION AND CLOSURE)

When corrective treatment is applied to road sections, intersections, drivers, or vehicles that had a poor accident record in the past, the safety effect of the treatment is properly estimated by comparing the number of accidents in a post-treatment period with the number of accidents that would have occurred in this period without the treatment. Earlier papers have shown that simple before-and-after comparisons are consistently biased; that is, treatments appear to be more effective than they really are. Accordingly, two methods--a nonparametric method and a Bayesian method--have been separately proposed for purging this bias. The nature of the bias and the two debiasing methods are reviewed. In the main body of the paper several data sets are used to compare the performance of the methods. In most cases the Bayesian method was found to yield better estimates.

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/trr/1984/975/975-007.pdf
• Summary URL:
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• Supplemental Notes:
  • Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved. Publication of this paper sponsored by Committee on Traffic Records and Accident Analysis.
• Corporate Authors:

  Transportation Research Board

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• Authors:
  • Persaud, Bhagwant N
  • Hauer, Ezra
• Discussers:
  • Pendleton, Olga J
• Publication Date: 1984

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 43-49
• Monograph Title: ANALYSIS AND MANAGEMENT OF TRAFFIC ACCIDENT RECORDS
• Serial:
  • Transportation Research Record
  • Issue Number: 975
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Bayes' theorem; Before and after studies; Crashes; Statistical bias
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors; I83: Accidents and the Human Factor;

Filing Info

• Accession Number: 00394917
• Record Type: Publication
• ISBN: 0309037573
• Report/Paper Numbers: HS-038 642
• Files: HSL, TRIS, TRB
• Created Date: Dec 31 1985 12:00AM