CATEGORICAL REGRESSION-ANALYSIS OF ACUTE EXPOSURE TO TETRACHLOROETHYLENE

Exposure-response analysis of acute noncancer risks should consider bo th concentration (C) and duration (T) of exposure, as well as severity of response. Stratified categorical regression is a form of meta-anal ysis that addresses these needs by combining studies and analyzing res ponse data expressed as ordinal severity categories. A generalized lin ear model for ordinal data was used to estimate the probability of res ponse associated with exposure and severity category. Stratification o f the regression model addresses systematic differences among studies by allowing one or more model parameters to vary across strata defined , for example, by species and sex. The ability to treat partial inform ation addresses the difficulties in assigning consistent severity scor es. Studies containing information on acute effects of tetrachloroethy lene in rats, mice, and humans were analyzed. The mouse data were high ly uncertain due to lack of data on effects of low concentrations and were excluded from the analysis. A model with species-specific concent ration intercept terms for rat and human central nervous system data i mproved fit to the data compared with the base model (combined species ). More complex models with strata defined by sex and species did not improve the fit. The stratified regression model allows human effect l evels to be identified more confidently by basing the intercept on hum an data and the slope parameters on the combined data (on a C x T plot ). This analysis provides an exposure-response function for acute expo sures to tetrachloroethylene using categorical regression analysis.