Document 1589ZrmoDE2qNKzDkRBobn46X

Quantitative risks of mesothelioma and lung cancer 601 Table 17. Derivation of correction factor for repotted mean exposure using assumed relative exposure and weighting factors by year of first employment in asbestos mines Data item Year of first employment Mean weighted by Before 1940 1941-JO 1951-60 1961-70 1971-80 Persons Expected lung cancer Relative exposure Crocidolite Amosite Weighting factors Persons Expected lung cancers >10 yr from 1st exposure 1' 1 62 1.68 1 .1 404 6.75 0.5 0.6 2355 17.59 0.25 0.35 2408 4.36 0.15 0.25 2088 0 0.35 0.44 Totals 7317 30.38 0.6 0.68 expected lung cancers in the five date of start groups is shown in Table 17. Table 17 also shows the numbers of individuals in each group, and the assumed relative levels of exposure. Mean exposures are calculated using the two alternative weightings. The expected lung cancer weighted means are larger than the corresponding person weighted means by a factor of 1.71 for crocidolite and 1.55 for amosite. The reported mean exposures have been adjusted using these factors for use in this review. Similar calculations for all cause deaths imply that the proportion of expected all cause deaths falling in the first 10 yr of follow up is 33%. The all cause mortality denominator for the observed mesotheli omas in the two subcohorts has therefore been reduced by a factor of 0.67. r / \