Estimation, testing and regression modeling of
subdistribution functions in competing risks, as described in Gray
(1988), A class of K-sample tests for comparing the cumulative
incidence of a competing risk, Ann. Stat. 16:1141-1154
, and Fine JP and
Gray RJ (1999), A proportional hazards model for the subdistribution
of a competing risk, JASA, 94:496-509, .