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excess relative risk due to exposure for unit concentration is the slope of relative risk with
concentration, obtained from the epidemiological analyses. Using the general model based on
cumulative exposure, as in the present calculations, the excess relative risk requires the slope coefficient
per concentration-year to be multiplied by the age in years for each age group in the table and to be
divided by the intermittency factor. Any ages that fall within the number of years of detection lag prior
to the target age have zero excess relative hazard. The modified table is completed in the manner of the
original table. The lifetime unit risk is then the following difference: the probability of lung cancer at the
target age in the table modified by exposure less the probability at the same age in the original table.
Use of the Garshick et al. (1987a) Case-Control Study to Estimate Unit Risk
The first study used to estimate lung cancer risk due to diesel exhaust exposure is the case-control study
of U.S. railroad workers by Garshick et al. (1987a). For this case-control study Garshick et al.
(1987a) collected 15,059 US railroad worker death records for 1981. They matched each of 1256
lung-cancer cases with 2 other deaths, each of those having nearly the same date of birth and death.
For each of the controls, death was due to a specified natural cause with no mention of cancer on the
death certificate. For each subject, Garshick et al. (1987a) determined years in a job with diesel
exposure, asbestos exposure and smoking history. Taking into account the effect of age, their analysis
used multivariate conditional logistic regression to determine the relationship between lung cancer and
duration of exposure to diesel exhaust. For workers with more than 20 years exposure and for
exclusion of shopworkers, they calculated the odds ratio was 1.55 (95% CI = 1.09, 2.21) with a
referent category of 0 to 4 years work in a job exposed to diesel exhaust.
From the odds ratio for a 20 year duration of exposure, the coefficient of increase with duration of
exposure was estimated by assuming a linear rise over the 20 years. Using a calculation similar to that
used by Garshick et al. with shopworkers included, the slope coefficient for the odds ratio is 0.022
(90% C.I. = 0.0071, 0.037) year -1 . Because the odds ratio approximates relative risk (Breslow and
Day, 1980, pp. 69-73), this value is approximately the rate of increase of relative risk (relative hazard)
and is used in a life table to obtain the lifetime unit risk. The modified life table calculation for unit
concentration (1 µg/m 3 ) for 5-yr. lag from carcinogenesis to death is in Table 7-1 of the diesel exhaust
TAC document (OEHHA, 1998). The resulting unit risks are presented in Point I in Table 7-3 of the
diesel exhaust TAC document. The highest values in that set are for the assumption that workers on
trains have a ramp (1,50) pattern of exposure. The 95% UCL for lifetime unit risk is 2.4 × 10 -3
(µg/m 3 ) -1 , with an MLE of 1.4 × 10 -3 (µg/m 3 ) -1 . For the roof (3,50) pattern of exposure, the procedure
is similar, but the exposure scale is increased by the ratio 65/22, representing the ratio of area under the
EF of the roof to the area under the EF of the block. The resulting 95% UCL for lifetime unit risk is 1.0
× 10 -3 (µg/m 3 ) -1 , with an MLE of 6.2 × 10 -4 (µg/m 3 ) -1 . The lowest values in the set are for the roof
(10,50) pattern of exposure. Using a similar approach, multiplying the exposure scale by the AUC ratio
of 191/22, the 95% UCL for lifetime unit risk is 3.6 × 10 -4 (µg/m 3 ) -1 , with an MLE of 2.1 × 10 -4
(µg/m 3 ) -1 .
Using the slope coefficient for the analysis including shopworkers, reported in Garshick et al. (1987a),
McClellan et al.(1989) previously calculated the expected increase in U.S. lung cancer deaths per year
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