Table 3

Model goodness of fit and association of lung cancer risk with alternative indicators of cumulative exposure to asbestos fibres, estimated by Poisson regression with adjustment for age, sex, race, calendar time and birth cohort

Exposure indicatorβSE (β)LR (df)pAIC
Biologically-based indices*
 Modified Lippmann Index (0.25≤D≤1 μm and L≥10 μm)0.002830.000730.027911.1 (1)0.0012341.6
 Berman Index0.018800.005510.03268.8 (1)0.0032343.9
 TEM fibres (D<0.25 μm and L≥10 μm)0.001710.000540.03218.3 (1)0.0042344.4
Ad hoc indices (μm-y)
 Mean fibre length0.008690.002570.07579.7 (1)0.0022343.1
 Mean fibre diameter0.150980.045580.07269.2 (1)0.0022343.5
 Mean fibre length0.019190.024000.13299.8 (2)0.0072344.9
 Mean fibre diameter−0.188350.42987−0.0735
  • * Units are f-y/ml. All of the indices also include the criterion that the aspect ratio (length:diameter) is at least 3:1.

  • Lippmann proposed minimum diameters of 0.15 μm or 0.3 μm, but we used a cut-off of ≥0.25 μm since that was the closest category in our TEM protocol.

  • AIC, Akaike Information Criterion (smaller values indicate better fit); β and SE, regression coefficient and associated standard error; ∆, change in lung cancer risk for increment in exposure equal to 1 IQR; D, diameter; L, length; LR (df), likelihood ratio test statistic (equivalent to χ2) with degree of freedom (df) and associated p value; TEM, transmission electron microscopy.