title: Planning sample sizes for before-after accident comparisons.
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.
authors.affiliation: School of Engineering, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224, United States. t.sando@nf.edu
authors.forename: Thobias
authors.initials: T
authors.lastname: Sando
authors.forename: Donna
authors.initials: D
authors.lastname: Mohr
mesh_terms: D000063:Accidents, Traffic / Q000517:prevention & control* / Q000706:statistics & numerical data*; D001499:Bayes Theorem; D004738:Engineering; D004779:Environment Design; D006801:Humans; D016013:Likelihood Functions; D008910:Minnesota; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data; D016012:Poisson Distribution; D012107:Research Design; D012449:Safety / Q000706:statistics & numerical data*; D018401:Sample Size