Planning sample sizes for before-after accident comparisons
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Published on: September 11, 2021
1School of Engineering, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224, United States. t.sando@nf.edu
Abstract:
Before-and-after safety studies are becoming more desirable in lieu of traditional cross-sectional studies in establishing crash modification factors, especially after the introduction of the first version of the Highway Safety Manual (2010). We present a simple method for estimating necessary sample sizes to obtain a target precision or power when the effect is represented as a proportional change in a Poisson rate. We also show that necessary sample sizes are not very different when full Bayesian models are implemented.
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