Bent Nielsen
  (1997)
  'Expected survival in the cox model'
  Scandinavian Journal of Statistics 24, p 275-287

  ABSTRACT:

  The survival in a group of patients is calculated using a
  Kaplan-Meier curve and the hypothesis that the survival can be
  predicted by a specified Cox hazard is studied. This Cox hazard
  is obtained from a previous study of similar patients. A simple
  test of the hypothesis is constructed by comparing a suitable
  average of the individual predicted survival curves with the
  observed survival. Three averaging procedures are presented;
  "direct adjusted survival curve", "Bonsel's survival curve" and
  "expected survival curve". Consistency and asymptotic
  distribution properties of the comparisons are discussed.