statistically significantly improved the likelihood (at the 5% significance
level) over the maximum likelihood of the model with only
cumulative BD ppm-years. Similarly, for all six endpoints, two of
the eight exposure covariates (cumulative STY ppm-years and
cumulative BD 6100 ppm-years) did not improve the likelihood
(at the 5% significance level) over the maximum likelihood of the
model with cumulative BD ppm-years alone.