Document yrGm90n5w8qXg68eKJpMX69XV

14256997033 2002-02-26 19:09:21 (GMT), page 43 42 Worker Interviews Since the QAMA exposure data did not measure exposures for most of the workers in the cohort, the QAMA-McGill researchers relied on company records to reconstruct exposures. Their reports on this "check" ofthe validity ofthe work records are contradictory. In 1971, Gibbs first reported. "Men were asked to relate dust conditions they remembered to those in areas where measurements had been made recently. In general, there was agreement among those we questioned." [Emphasis added] (Gibbs and LaChance 1974) However in 1984 Liddell reported, t "Over the years, we had come across several inconsistencies and other evidence of errors in work histories. We took this opportunity to attempt correction where appropriate, but for reasons outlined elsewhere, we were unable to make use ofthis effort Many ofthe changes in work history, elicited by `blind' field inquiry and checked against company files, were certainly justified but we have not made them, and so allowed errors to remain." [Emphasis added] (Liddell et al. 1984) Even after recognizing their errors they ignored them: "However, this type of error appears to have been distributed unevenly, and so like might not have been compared to like. In case-referent comparisons, minor random unbiased exposure errors are probably less serious than bias; we therefore returned to the situation that existed before the field work was instituted." (Liddell et al. 1984) The QAMA-McGill researchers provided no analysis of the magnitude or randomness of the errors. No effort was made to compare the interviews with the written record to determine whether or not the written records contained a systematic bias. of 2, 5, 7,10 over the next four years. 42