The influence of categorising survival time on selection and estimation of time-varying effects in an extended Cox model

Anika Buchholz, Willi Sauerbrei & Patrick Royston
Background: With longer follow-up times, the proportional hazards assumption is questionable in the Cox model. Cox already suggested to include an interaction between a covariate and a function of time, i.e. a time-varying effect. Since then, several approaches have been proposed for modelling time-varying,[for full text, please go to the a.m. URL]