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How does a strataterm fit a Cox model?
A strataterm identifies a stratified Cox model; separate baseline hazard functions are fit for each strata. The clusterterm is used to compute a robust variance for the model. The term + cluster(id)where each value of idis unique is equivalent to specifying the robust=Targument.
What are the assumptions of the Cox model?
The Cox (PH) model: (tjZ(t)) = 0(t) expf 0Z(t)g Assumptions of this model: (1) the regression e ect is constant over time (PH assump-tion) (2) linear combination of the covariates (including possibly higher order terms, interactions) (3) the link function is exponential The PH assumption in (1) has received most attention in
How is a strataterm used in a model equation?
There are three special terms that may be used in the model equation. A strataterm identifies a stratified Cox model; separate baseline hazard functions are fit for each strata. The clusterterm is used to compute a robust variance for the model.
Which is the best method for Cox regression?
Nearly all Cox regression programs use the Breslow method by default, but not this one. The Efron approximation is used as the default here, it is more accurate when dealing with tied death times, and is as efficient computationally.
In that case, the treatment effect has a population-averaged (marginal) interpretation, the effect being averaged over all centres. It is known that the Cox model leads to a consistent estimate of the population hazard ratio (under some mild conditions, I guess), but the standard error is not because of the correlation between the survival times.
How is the Cox model used in survival analysis?
Alternatively, multilevel modelling can also be used for such type of data, as you suggest. That is, the centre effect enters the Cox model as a random effect. In survival analysis, this is called a frailty model.
How is the centre effect entered into the Cox model?
The method is available in R (cf. the cluster () function to be used within coxph () ). Alternatively, multilevel modelling can also be used for such type of data, as you suggest. That is, the centre effect enters the Cox model as a random effect.