01504374

Component

http://onlinepubs.trb.org...rences/2011/RSS/1/Ye,Z.pdf

The modeling of relationships between motor vehicle crashes and underlying factors has been investigated for more than three decades. Recently, many highway safety studies have documented the use of Poisson regression models, negative binomial (NB) regression models or both. Pearson’s 2 X and the scaled deviance ( 2 G ) are two common test statistics that have been proposed as measures of goodness-of-fit (GOF) for Poisson or NB models. Unfortunately, transportation safety analysts often deal with crash data that are characterized by low sample mean values. Under such conditions, the traditional test statistics may not perform very well. This study has two objectives. The first objective is to examine the accuracy and reliability of traditional test statistics for the GOF of accident models subjected to low sample means. The second objective intends to identify a superior test statistic for evaluating the GOF of accident prediction models. For Poisson models, this paper proposes a better yet easy to use test statistic (Power-Divergence) that can be applied for almost all sample mean values, except when the mean value is extremely low, for which no traditional test statistic can be accurate. For Poisson-Gamma models, this study demonstrates that traditional test statistics are not accurate and robust. A more complex method (grouped G(2)) proposed in a previous study is recommended. Guidance on the use of the grouped G(2) methods is further provided. Examples using observed data are sued to help illustrate the performance of different test statistics and support the findings of this study.

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

01501394

English

21p

2011

3rd International Conference on Road Safety and Simulation

Digital/other

Figures; References; Tables

Crash data; Goodness of fit; Highway safety; Poisson distributions; Regression analysis; Statistical analysis; Traffic crashes

Highways; Safety and Human Factors; I80: Accident Studies

TRIS, TRB, ATRI

Jan 9 2014 3:59PM