For all leukemia, four of the eight exposure covariates (cumulative
DMDTC mg/cm-years, cumulative # of BD HITs, cumulative #
of STY HITs, and cumulative STY >50 ppm-years) significantly (at
the 1% significance level) improve the maximum likelihood over
the model with cumulative BD ppm-years alone. The slope (per
cumulative BD ppm-year) of the Cox proportional-hazards model
for leukemia is statistically significantly different than zero before
adding any of the eight exposure covariates; however, the slope is
not statistically significantly different than zero after any one of
the eight exposure covariates is added to the Cox proportional hazards
model. Furthermore, Sielken and Valdez-Flores [23] show that
the slope is not statistically significantly different than zero when
the exposure–response modeling is based on the person-years
with cumulative BD ppm-years less than or equal to
200 ppm-years even with no other covariates in the model.
For CLL, none of the covariates significantly improves the maximum
likelihood at the 5% significance level. The slope is statistically
significantly different than zero when the model includes
BD ppm-years alone. However, Sielken and Valdez-Flores [23]
showed that the slope is not statistically significantly different
than zero when the exposure–response modeling is based on the
person-years with cumulative BD ppm-years less than or equal
to 300 ppm-years.
For lymphoid neoplasm (which include CLL), none of the covariates
significantly improves themaximumlikelihood at the 1% significance
level and only cumulative # of STY HITs improves the
maximumlikelihood at the 5% significance level. The slope is statistically
significantly different than zero when the model includes BD
ppm-years alone.However, SielkenandValdez-Flores [23] showthat,
when the exposure–response modeling is based on the person-years
with cumulative BD ppm-years less than or equal to 400 ppm-years,
the slope is not statistically significantly different than zero.
For CML and AML and myeloid neoplasms, the slope is not statistically
significantly different than zero when the model includes