
This post has NOT been accepted by the mailing list yet.
I have developed a risk scoring system that I'm trying to validate. It was
originally developed in one cohort, and I am now validating it in a new,
independent, cohort. However, I am unsure how to test for goodnessoffit
using HosmerLemeshow's test.
First question: When validating my score, is it not correct that I should use
the observed mortality (my endpoint) from the development cohort to estimate
the expected mortality in my validation cohort?
Second question: When calculating the Chisquare between the observed and
expected mortality, should my formula not be: (observedexpected)^2/
(expected*1expected/N (in this stratum))?
Third question: How many degrees of freedome should I use? When I read the
book by Hosmer and Lemeshow (Applied logistic regression), in the section on
validation in an external cohort, I understand that the number of groups
equal the degrees of freedom, which in different from the ordinary method in
which the degrees of freedom is groups2. Is this correct?
Thanks!
Mikkel
