Read full paper at: http://www.scirp.org/journal/PaperInformation.aspx?PaperID=52865#.VKtEO8nQrzE Author(s) Anika Buchholz 1 , Willi Sauerbrei 1 , Patrick Royston 2 Affiliation(s) 1 Center for Medical Biometry and Medical Informatics, Medical Center - University of Freiburg, Freiburg, Germany . 2 MRC Clinical Trials Unit at University College London, London, UK . ABSTRACT A standard approach for analyses of survival data is the Cox proportional hazards model. It assumes that covariate effects are constant over time, i.e. that the hazards are proportional. With longer follow-up times, though, the effect of a variable often gets weaker and the proportional hazards (PH) assumption is violated. In the la...
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