[R] time dependency of Cox regression

[array chip]

Hi,

How can I specify a Cox proportional hazards model
with a covariate which i believe its strength on
survival changes/diminishes with time? The value of
the covariate was only recorded once at the beginning
of the study for each individual (e.g. at the
diagnosis of the disease), so I do not have the time
course data of the covariate for any given individual.
For example, I want to state at the end of the
analysis that the hazard ratio of the covariate is 6
at the beginning, decrease to 3 after 2 years and
decrease to 1.5 after 5 years.

Is this co-called time-dependent covariate? I guess
not, because it's really about the influence of the
covariate (which was measured once at the beginning)
on survival changing over time.

Thanks for any input.


		
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