Use of a job-exposure matrix to assess occupational exposures in relation to birth defects

Accurate exposure assessment remains a challenge in occupational epidemiolo gy. We evaluated one approach, use of a job-exposure matrix (JEM), by apply ing the National Institute for Occupational Safety and Health (NIOSH) JEM t o a large case-control birth defects study that included parental occupatio n information. We investigated the JEM exposure predictions in several ways and found that for a substantial proportion of the parents in the birth de fects study, the JEM yielded either no exposure data or nonsense prediction s. Among exposure predictions that were plausible, most were of low probabi lity. The high probability exposure predictions were statistically unstable , and neither low nor high probability exposure predictions were reliable. There was considerable discrepancy between the JEM predictions and expert a ssessments for five exposures of interest. Application of the NIOSH JEM to the birth defects study database (and probably other databases as well) doe s not provide a useful means of assessing occupational exposures.