STATISTICAL INJURY INCIDENCE RATE COMPARISONS

Statistical methods for comparing two or more injury incidence rates a re presented as an aid in selecting operations for ergonomic intervent ion to reduce work place injuries. The methods assume that injuries oc cur according to a Poisson process and the analysis is conditional on the total number of injuries. Methods presented include hypothesis tes ts to compare the ratio of two injury incidence rates and hypothesis t ests to compare more than two rates. The power of these comparisons in creases with the total number of injuries observed, the Type I error p robability, and as the ratio of the injury exposure periods approaches one. Expressions for simultaneous confidence intervals for two or mor e rates and for the ratios of two or more rates are also given. These general statistical methods can be implemented easily on a personal co mputer.