International Journal of Epidemiology, Vol 22, S72-S82, Copyright © 1993 by International Epidemiological Association
B Stengel, P Pisani, JC Limasset, J Bouyer, F Berrino and D Hemon
Correct retrospective assignment of subjects to an exposure category is
affected by a variety of problems: 1) lack of an objective lifetime
measurement; 2) dependence upon the accuracy and thoroughness of the job
description; 3) heavy reliance upon the knowledge of experts. The aim of
the study was the quantification of the performance of a job exposure
matrix (JEM) in evaluating solvent exposure, using expert judgements 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) and 765 controls, the other
298 cases of glomerulonephritis (GN) and 298 controls. The JEM had been set
up previously for a case- control study on laryngeal cancer and is based on
4000 discrete job titles. Comparison between the JEM and expert exposure
evaluation was carried out for 2736 job periods in the BC study and 929 in
the GN study. Categories of exposure for both experts and JEM were
dichotomized, using different 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 design and of the inclusiveness of the definition of
exposure. Sensitivity of the JEM vis-a-vis the experts was low (23-63%),
whereas specificity was rather high (87-98%). The best concordance between
the two methods was obtained with a specific dichotomy from the JEM and a
narrow definition of exposure by the experts. Bias and loss of power
resulting from JEM misclassifications were calculated with a theoretical
population odds ratio of 3 and an exposure prevalence of 10%. If the
experts' classification of the subjects according to exposure is assumed to
be 100% correct, using the JEM led to a bias in estimating the odds ratio,
ranging from 1.5 to 2.1, and to a loss of power equivalent to a reduction
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 and arose from
different sources: 1) inadequate job descriptions, related 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.(ABSTRACT TRUNCATED AT 400
WORDS)
ARTICLES
Retrospective evaluation of occupational exposure to organic solvents: questionnaire and job exposure matrix
INSERM U.170, Villejuif, France.
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