Goodness of fit: Stare J.,Pohar Perme M., Henderson R. (2005)
"Goodness of fit of relative survival models." Statistics in Medicine,
24: 3911--3925.
Package. Pohar M., Stare J. (2006) "Relative survival analysis in R."
Computer Methods and Programs in Biomedicine, 81: 272--278
Relative survival: Pohar, M., Stare, J. (2007) "Making relative survival
analysis relatively easy." Computers in biology and medicine, 37:
1741--1749.