home edit2 whole TSD November 2002 PDF format - OEHHA

procedure (NLIN), the parameters were estimated at:
α ∧ = 0.500 (unitless parameter) and
∧
β = 0.0017 (cumulative mg-days/m 3 ) -1
the 95% (two-tailed) upper confidence limit for β was 0.0079, and the χ 2 goodness-of-fit statistic was
0.15 (1 df, p = 0.70). Lung cancer deaths predicted by the model were compared with the observed
lung cancer deaths for the three exposure groups (Table 7).
Table 7:
Lung Cancer Deaths Among Cadmium-Exposed Workers: Observed And Predicted
(Data of Thun et al., 1985)
Cumulative Exposure Groups
Low Middle High
Observed 2 6 7
Predicted * 2.94 5.99 7.44
* Linear relative risk model with healthy worker effect, U.S. controls.
With these estimates of the parameters, the model was then applied to the California population to
predict the excess number of lung cancer deaths induced by cadmium exposure. First, a current life
table was produced for California males and females separately, using five-year age intervals. The
background hazard of lung cancer death for each five-year age interval was calculated using 1980
census data for California (Bureau of the Census, 1982) and age-specific death rates for California from
1979-80 vital statistics data (California Department of Health Services, 1982) by standard statistical
techniques (Chiang, 1984). These were then summed over a lifetime.
Next, using the estimated value for β and setting α = 1 for the general population (i.e. no healthy
worker effect), the hazard of lung cancer death given a continuous lifetime exposure to 1 µg/m 3 cadmium
was calculated from the model. Using these hazard rates, a new life table was constructed. Subtracting
the background probability of a lung cancer death from that obtained for an exposed population resulted
in a range of risk for excess lifetime cancer from 2 × 10 -3 to 1.2 × 10 -2 (µg/m 3 ) -1 . CDHS also suggested
that a “best” cancer unit risk value for regulatory purposes was 1.6 × 10 -3 (µg/m 3 ) -1 for cadmium in air.
CDHS (1990) reviewed the previous CDHS (1986) estimate of parameters generated from the fit of
the Poisson regression model to the Thun et al. (1985) lung tumor data. The 97.5% upper confidence
limit for β was calculated for a number of values of α that were in the range 0.5 < α < 1.0. All of the
calculated 97.5% upper confidence limit for β were less than the corresponding values calculated from
the statistical analysis program used previously by CDHS (1986).
CDHS (1990) decided that it is reasonable to restrict α to values between 0.5 and 1.0. If α were less
158