SOURCES OF DISCREPANCIES BETWEEN A JOB EXPOSURE MATRIX AND A CASE BY CASE EXPERT ASSESSMENT FOR OCCUPATIONAL EXPOSURE TO FORMALDEHYDE AND WOOD-DUST

Two methods used for retrospective evaluation of occupational exposure s, a case by case assessment by expert and the application of a job ex posure matrix (JEM), are compared using occupational histories collect ed for a case-control study on sinonasal cancer. The objective was to identify the main sources of discrepancies and to contribute to an opt imal use of a JEM for population-based case-control studies. Compariso ns were based on job periods, and were performed separately for two su bstances: formaldehyde and wood-dust. Job periods were classified acco rding to the category of exposure assigned by the matrix, and to the p robability and revel of exposure assessed by the study expert. The sou rces of discrepancies were examined for job periods probably or defini tely exposed according to the JEM and unexposed for the expert, or une xposed in the JEM and probably or definitely exposed to medium or high level for the expert. Such discrepancies were observed for 8% of the job periods for formaldehyde and 3% of the job periods for wood-dust. The agreement between the two approaches was better for wood-dust than for formaldehyde. The relative importance of different sources of dis crepancies was not the same for formaldehyde and wood-dust. For formal dehyde a substantial part of the discrepancies was due to disagreement s between the study expert and the matrix experts, which were mostly d ifferences in threshold limits between 'not exposed' and 'definitely e xposed at a low level'. Differences between experts' opinions did not explain the discordances observed for wood-dust. The presence of addit ional information in the questionnaire was an important source of disc repancy for the two substances. However in situations where additional information from the questionnaire is important, the fact that the ma trix is insufficient or inadequate can often be foreseen: time-depende nt exposure in the matrix, complex job with multiple activities diffic ult to code, additional part-time job, and a limited list of occupatio ns. With a semi-structured questionnaire, the two methods could be use d in a complementary way, with an evaluation by experts from the quest ionnaire limited to these situations, and with a direct application of the matrix for the other jobs.