Planning sample sizes for before-after accident comparisons
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. © 2011 Elsevier Ltd. All rights reserved.
Accident Analysis and Prevention
Digital Object Identifier (DOI)
Sando, & Mohr, D. (2012). Planning sample sizes for before–after accident comparisons. Accident Analysis and Prevention, 45, 826–827. https://doi.org/10.1016/j.aap.2011.08.005