Tl. Lash et al., A METAANALYSIS OF THE RELATION BETWEEN CUMULATIVE EXPOSURE TO ASBESTOS AND RELATIVE RISK OF LUNG-CANCER, Occupational and environmental medicine, 54(4), 1997, pp. 254-263
Objectives-To obtain summary measures of the relation between cumulati
ve exposure to asbestos and relative risk of lung cancer from publishe
d studies of exposed cohorts, and to explore the sources of heterogene
ity in the dose-response coefficient with data available in these publ
ications. Methods-15 cohorts in which the dose-response relation betwe
en cumulative exposure to asbestos and relative risk of lung cancer ha
s been reported were identified. Linear dose-response models were appl
ied, with intercepts either specific to the cohort or constrained by a
random effects model; and with slopes specific to the cohort, constra
ined to be identical between cohorts (fixed effect), or constrained by
a random effects model. Maximum likelihood techniques were used for t
he fitting procedures and to investigate sources of heterogeneity in t
he cohort specific dose-response relations. Results-Estimates of the s
tudy specific dose-response coefficient (k(I.i)) ranged from zero to 4
2 x 10(-3) ml/fibre-year (ml/f-y). Under the fixed effect model, a max
imum Likelihood estimate of the summary measure of the coefficient ((k
) over cap(1)$) equal to 0.42 x 10(-3) (95% confidence interval (95% C
I) 0.22 to 0.69 x 10(-3)) ml/f-y was obtained. Under the random effect
s model, implemented because there was substantial heterogeneity in th
e estimates of k(I.i) and the zero dose intercepts (A(i)), a maximum l
ikelihood estimate of (k) over cap(1)$ equal to 2.6 x 10(-3) (95% CI 0
.65 to 7.4 x 10(-3)) ml/f-y, and a maximum likelihood estimate of a eq
ual to 1.36 (95% CI 1.05 to 1.76) were found. Industry category, dose
measurements, tobacco habits, and standardisation procedures were iden
tified as sources of heterogeneity. Conclusions-The appropriate summar
y measure of the relation between cumulative exposure to asbestos and
relative risk of lung cancer depends on the context in which the measu
re will be applied and the prior beliefs of those applying the measure
. In most situations, the summary measure of effect obtained under the
random effects model is recommended. Under this model, potency, (k) o
ver cap(1)$, is fourfold lower than that calculated by the United Stat
es Occupational Safety and Health Administration.