The excess risk was characterized using the estimated effective
ppm concentration (EC) corresponding to an extra risk of
1/100,000 and the unit risk factor (URFmle) corresponding to a
linear extrapolation below the EC(1/100,000). Excess risk was also characterized as the 95% lower confidence limit (LEC(1/100,000))
on the concentration corresponding to an extra risk of 1/100,000
and the upper-bound unit risk factor (URFub) corresponding to a
linear extrapolation below the LEC(1/100,000).
Life-table methods were used to calculate excess risks (ECs and
LECs). These calculations are sequential calculations beginning at
age zero that step through the years in a lifetime. The calculation
incorporates the background age-specific hazard rate for
all-cause mortality, the background age-specific hazard rate for
the specified response, the age-specific values for the exposure
metrics, and the corresponding Cox exposure–response model
(i.e., the age-specific multiplier of the background age-specific hazard
rate for the specified response determined from the fitted Cox
exposure–response model and the values of the age-specific exposure