Assessment of occupational exposures in a general population: comparison of diVerent methods

Objectives—To evaluate the relative merits of job specific questionnaires and various alternative assessment methods of occupational exposures often used in general population studies. Methods—Subjects were participants in a hospital based case-control study of risk factors for male infertility. Estimates of exposure to organic solvents and chromium, based on job specific questionnaires, generic questionnaires, self reports of exposure, an external job exposure matrix (JEM), and a population specific JEM were compared with passive diVuse dosimeter results and measurements in urine. Urine samples from the end of the shift were analysed for metabolites of toluene, xylene, several glycol ethers, trichloroethylene, and chromium. Passive dosimeter date, metabolites of specific solvents, and urinary chromium concentrations were available for 89, 267, and 156 subjects, respectively. The alternative methods and measurements in urine were compared by means of the Cohen’s ê statistic and by computing the positive predictive value, sensitivity, and specificity of the alternative methods against measurements in urine. Results—Passive dosimeter results indicated that exposure classifications with job specific questionnaire information could discriminate between high and low exposures. The ê coeYcients were <0.4, so agreement between the various methods and measurements in urine was poor. Sensitivity of the methods ranged from 0.21 to 0.85, whereas specificity ranged from 0.34 to 0.94. Positive predictive values ranged from 0.19 to 0.58, with the highest values for job specific questionnaires. Conclusions—The results indicate that the implementation of job specific questionnaires in a general population study might be worth the extra expense it entails, bearing in mind the paramount importance of avoiding false positive exposure estimates when exposure prevalence is low. (Occup Environ Med 1999;56:145–151)