Location

Bolton Landing, New York

Date

20-6-2013

Session

Session 8 – Hybrid Presentations

Abstract

When analyzing naturalistic driver performance data, different analysis methods can have large impacts on safety estimates for the condition being assessed. To illustrate, this paper reanalyzed the data for a secondary task (conversation on a hand-held cell phone) from the recently-released Virginia Tech Transportation Institute (VTTI) 100-Car databases, using a standard method for epidemiological analysis. It found substantially lower estimates for the odds ratio (OR), population exposure percent (Pe%), and population attributable risk percent (PAR%) than with the VTTI analysis method. The crash/near-crash OR was reported by VTTI as 1.29, but was found to be 0.78 with the standard method, a reversal in direction from a potentially crash-increasing to a potentially crash-reducing effect. The Pe% for crashes/near-crashes was 12.5% using the VTTI method, but declined to 6.7% with the standard method. The PAR% was reported as 3.6% but a population preventive fraction of 1.5% (a protective effect) was estimated by the standard method. The OR difference was traced to an “assumption bias” in the VTTI method that had unequal effects for the unexposed vs. exposed cases. The Pe% and PAR% differences were traced to an error in the VTTI calculation of Pe%. This bias and error were systemic in the VTTI analysis methods, overestimating OR, Pe%, and PAR% for all tasks examined. Future research should seek to better understand the epidemiologic analysis methods that are most appropriate in the new and emerging field of naturalistic driving research.

Rights

Copyright © 2013 the author(s)

DC Citation

Proceedings of the Seventh International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design, June 17-20, 2013, Bolton Landing, New York. Iowa City, IA: Public Policy Center, University of Iowa, 2013: 509-515.

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Jun 20th, 12:00 AM

Naturalistic Studies of Driver Distraction: Effects of Analysis Methods on Odds Ratios and Population Attributable Risk

Bolton Landing, New York

When analyzing naturalistic driver performance data, different analysis methods can have large impacts on safety estimates for the condition being assessed. To illustrate, this paper reanalyzed the data for a secondary task (conversation on a hand-held cell phone) from the recently-released Virginia Tech Transportation Institute (VTTI) 100-Car databases, using a standard method for epidemiological analysis. It found substantially lower estimates for the odds ratio (OR), population exposure percent (Pe%), and population attributable risk percent (PAR%) than with the VTTI analysis method. The crash/near-crash OR was reported by VTTI as 1.29, but was found to be 0.78 with the standard method, a reversal in direction from a potentially crash-increasing to a potentially crash-reducing effect. The Pe% for crashes/near-crashes was 12.5% using the VTTI method, but declined to 6.7% with the standard method. The PAR% was reported as 3.6% but a population preventive fraction of 1.5% (a protective effect) was estimated by the standard method. The OR difference was traced to an “assumption bias” in the VTTI method that had unequal effects for the unexposed vs. exposed cases. The Pe% and PAR% differences were traced to an error in the VTTI calculation of Pe%. This bias and error were systemic in the VTTI analysis methods, overestimating OR, Pe%, and PAR% for all tasks examined. Future research should seek to better understand the epidemiologic analysis methods that are most appropriate in the new and emerging field of naturalistic driving research.