You might try a log-normal or log-logistic accelerated failure time model. These models dictate decreasing hazard ratios over time for baseline covariates.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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Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
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