Document 3QERgwwDBREa0mjX2jvxOZKvE

14256997033 2002-02-26 19:09:21 (GMT), page 48 47 Another Dose Correction In the 1980 paper McDonald justified the age 45 cut off because "by this time most of the men had completed their service" but this was not true.(McDonald et al. 1980b) In 1997 they revealed that over 2400 men in the 1890-1920 study cohort were still employed in 1967 and the youngest of these was 47. Since the age 45 cut offno longer produced the linear dos-response curve they sought, in 1997 they calculated exposures up to age 55. Rather than using exposure data that had been obtained after 1966, the year the QAMA-McGill studies began, they used the already discredited pre-1966 data to estimate these exposures. They also altered the dose % calculation methodology because, "it did not prove feasible to use the same methods as previously.''(Liddell et al. 1997a) They do not provide any rational for this change (except perhaps for large computer file size) nor do they provide a comparative analysis of results using the "old" and "new" dose estimate methods. "As over 2400 men in the cohort were still employed in 1967, attempts were made to estimate exposures yearly up to 1985, when the last man had retired. It did not prove feasible to use the same methods as previously. Instead, each man was allocated dust levels as follows: for 1967, the same level as in 1966; for each subsequent year, a proportion ofthat level in accordance with the average trend of fibre concentration for his specific mine or mill. From these levels, we estimated yearly exposures from 1967 to 1985 (McDonald et. al., 1993), and extended each man's exposure record by a further 19 years. To give much-needed greater flexibility for the calculation of exposures-to the age of 55, for instance, or, for case-referent analyses, in relation to the age at death of the case-the exposure file was re-organized: first, the annual record ofexposure, incorporating the adjustment for length ofthe working week, was changed to the dust 47