EFFICIENCY OF DIFFERENT GROUPING SCHEMES FOR DUST EXPOSURE IN THE EUROPEAN CARBON-BLACK RESPIRATORY MORBIDITY STUDY

Objectives-The aim of this study was to assess the theoretical efficie ncies of different grouping strategies and its effect on the exposure- response relation in a study of respiratory morbidity associated with exposure to total inhalable and respirable carbon black dust. Methods- A large epidemiological study is being undertaken to investigate the r espiratory health of employees in the European carbon black manufactur ing industry in relation to exposure to carbon black dust. In phase 2 of the study, repeated measurements of total inhalable and respirable dust were taken which enabled estimation of various components of vari ability in the exposure data (within and between worker variance and w ithin and between group variance). These variance components were used to calculate the contrast in exposure between the groups in various c lassification schemes and to calculate the theoretical attenuation of the exposure-response relation and the standard error (SE) of the slop e. Results-High contrast in exposure was found when workers were class ified according to the combination of their factory and job category a s well as when these combinations were amalgamated into five exposure groups. Attenuation was minimal with most grouping schemes; only with the individual based strategy was the attenuation large. The SE of the theoretically attenuated exposure-response slope was smallest for the strategy based on individual people followed by the classification sc heme based on factory and job category. Conclusions-It was concluded t hat, although some assumptions for the calculations of the attenuation of the exposure-response slope were not met, the most appropriate cla ssification scheme of the worker seems to be by the combination of fac tory and job category.