Utility function that returns a data.frame containing basic demographic
information compatible with the md.survnp,
md.survcox and md.impute functions.
md.D(age, sex, year)vector of patient ages specified as number of days or number of years.
vector containing 1 for males and 2 for females
vector of years of entry into the study can either be supplied as vector of start dates or as vector of years specified in number of days from origin (1-1-1970).
md.survcox, md.survnp