RETROSPECTIVE EVALUATION OF OCCUPATIONAL EXPOSURE TO ORGANIC-SOLVENTS- QUESTIONNAIRE AND JOB EXPOSURE MATRIX

Correct retrospective assignment of subjects to an exposure category i s affected by a variety of problems: 1) lack of an objective lifetime measurement; 2) dependence upon the accuracy and thoroughness of the j ob description; 3) heavy reliance upon the knowledge of experts. The a im of the study was the quantification of the performance of a job exp osure matrix (JEM) in evaluating solvent exposure, using expert judgem ents as the reference method. The sources of discrepancies between the two methods were analysed within the framework of two community-based case-control surveys. One included 765 cases of bladder cancer (BC) a nd 765 controls, the other 298 cases of glomerulonephritis (GN) and 29 8 controls. The JEM had been set up previously for a case-control stud y on laryngeal cancer and is based on 4000 discrete job titles. Compar ison between the JEM and expert exposure evaluation was carried out fo r 2736 job periods in the BC study and 929 in the GN study. Categories of exposure for both experts and JEM were dichotomized. using differe nt cutoff points for exposure and non-exposure. Prevalence of exposure as assessed by the experts was twice as high in the GN study (19%) as in the BC study (10%), showing the importance of the questionnaire de sign and of the inclusiveness of the definition of exposure. Sensitivi ty of the JEM vis-a-vis the experts was low (23-63%), whereas specific ity was rather high (87-98%). The best concordance between the two met hods was obtained with a specific dichotomy from the JEM and a narrow definition of exposure by the experts. Bias and loss of power resultin g from JEM misclassifications were calculated with a theoretical popul ation odds ratio of 3 and an exposure prevalence of 10%. If the expert s' classification of the subjects according to exposure is assumed to be 100% correct, using the JEM led to a bias in estimating the odds ra tio. ranging from 1.5 to 2.7, and to a loss of power equivalent to a r eduction in the number of subjects by a factor of 5 to 10. Analysis of systematic discrepancies between exposure assessments of the experts and the JEM showed that they were clustered with some job categories a nd arose from different sources: 1) inadequate job descriptions, relat ed to the codification system adopted and necessitating the gathering of information at the individual level; 2) true disagreements between JEM and experts regarding the definition of solvent exposure. These di sagreements were analysed in detail and led. in some cases, to questio n the use of experts as a gold standard.