RELIABILITY OF AN EXPERT RATING PROCEDURE FOR RETROSPECTIVE ASSESSMENT OF OCCUPATIONAL EXPOSURES IN COMMUNITY-BASED CASE-CONTROL STUDIES

The most daunting problem in community-based studies of occupational c ancer is retrospective exposure assessment. To avoid the error involve d in using job title as the exposure variable or self-report of exposu re, our team developed an approach based on expert judgment applied to job descriptions obtained by interviewers. A population-based case-co ntrol study of cancer and occupation was carried out in Montreal betwe en 1979 and 1986, and over 4,000 job histories were assessed by our te am of experts. The job histories of these subjects were evaluated, by consensus, by a team of chemist/hygienists for evidence of exposure to a list of 294 workplace chemicals. In order to evaluate the reliabili ty of this exposure assessment procedure, four years after the rating was completed we selected 50 job histories at random and had two membe rs of the expert team carry out tile same type of coding, blind to the original ratings for these jobs. For 25 job histories, comprising 94 distinct jobs, the pair worked as a consensus panel; for the other 25, comprising 92 distinct jobs, they worked independently. Statistical c omparisons were made between the new ratings and the old. Among those rated by consensus, the marginal distribution of exposure prevalence,v as almost identical between old and new. The weighted kappa for agreem ent was 0.80. Among items for which both ratings agreed that there had been exposure, there,ras good agreement on the frequency, concentrati on, and route of contact. When the two raters worked independently, th e levels of agreement between them and between each of them and the or iginal rating was good (kappas around 0.70), though not as high as whe n they worked together: It is concluded that high levels of reliabilit y are attainable for retrospective exposure assessment by experts. (C) 1997 Wiley-Liss, Inc.