RELIABILITY OF RETROSPECTIVE CHLOROPHENOL EXPOSURE ESTIMATES OVER 5 DECADES

For a cohort study of chlorophenate-exposed sawmill workers, historica l exposures from the 1940s to the 1980s were estimated by teams of 9-2 0 employees (each interviewed individually The mill histories were div ided into eras when jobs and exposures were relatively stable. Raters with at least 5 years of work experience in an era were asked to estim ate the frequency and duration of exposure for each job in the mill. R eliability measures for these estimates were calculated for each of th e 39 mill and time period combinations, using the individual intraclas s correlation coefficient (ICCind) to assess agreement between raters and the group intraclass correlation coefficient (ICCgroup) to assess the stability of the mean estimates of exposure. ICCind were low, with means that increased from 0.23 to 0.35 over the five decades. ICCgrou p were considerably higher (means increasing from 0.78 to 0.88 over ti me), indicating that the number of raters used in this study was suffi cient to produce stable average estimates of exposure throughout the s tudy period. These data confirm the intuitive expectation that reliabi lity of exposure estimates decreases when reconstruction of conditions in the distant past is required, and therefore that the random compon ent of exposure misclassification is a greater threat to validity in t hese earlier time periods. (C) 1996 Wiley-Liss, Inc.