I'm doing some coxph() analyses with a large and complex dataset. The
data was collected in different centers, so I am using
strata(centers) to stratify the analysis.
My main issue is, not all centers collected all the variables, so for
a model such as:
coxph(Surv(days, cancer) ~ varA + sex + strata(centers), data)
I might have 1 or more centers that have NA for varA (in practice,
all the individuals monitored at those centers come without varA).
coxph() obviously warns me that a number of individuals have been
excluded -- would that be equivalent to doing the analysis on a
subset of the data or not?
It seems so by definition to me. I am confused as to what else would be
happening. You can always create a smaller, easier to understand
dataset and try things out for yourself. Perhaps I do not understand
your question though.
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