26 Jan, 11 | by lelliott
Dr. Burstyn, in his commentary , underscores the critical importance of using the best exposure assessment methods possible to minimize misclassification. We agree about the value of expert formulated models for systematically and transparently documenting exposure assessment, but caution that many existing studies may not be readily adapted to such model building. For such studies, the best alternative exposure assessment methodology should be employed, such as job-exposure matrices (JEMs) or expert assessments of self-reported work histories. Even though the relationships between the true exposure and estimates by expert assessment and a JEM are unknown (which is the case for most exposure assessments) we believe that understanding the differences between the two methods is informative, especially given the considerable time and resources necessary to carry out an expert assessment.
As Dr. Burstyn indicates , neither assessment approach used in our study  allows us to claim that lead definitely causes brain tumors. However, if this is the standard for judging the success of an exposure assessment method, most methods are failures. Although only suggestive, we do see some evidence of an association and indicate that future studies would benefit from the most accurate exposure assessment method available. The intent of our analysis was to compare two widely used approaches and to encourage epidemiologists to pursue the best exposure assessment methods possible. We acknowledge limitations with the expert assessment approach and strongly support the development and use of new exposure assessment methods. However, expert assessment may be the best approach available to an existing study and could reveal important associations that future studies can explore in greater detail using more refined exposure assessment techniques.
Martha S. Linet
Peter D. Inskip
1. Burstyn I. The ghost of methods past: exposure assessment versus
job-exposure matrix studies. Occup Environ Med 2011;68:2-3 doi:10.1136/oem.2009.054585. (Available at http://oem.bmj.com/content/68/1/2.full?sid=f61a67b1-71a0-4c03-95b1-008ff222dad0)
2. Bhatti P, Stewart PA, Linet MS, Blair A, Inskip PD, Rajaraman P.
Comparison of occupational exposure assessment methods in a case-control study of lead, genetic susceptibility and risk of adult brain tumours. Occup Environ Med 2011;68:4-9 doi:10.1136/ oem.2009.048132. (Available at http://oem.bmj.com/content/68/1/4.full?sid=d3fd91dc-5af2-4fe6-8b38-555288c097e0)