From model building to validation and back: a plea for robustness.

This paper is the written version of the President's invited lecture speaker at the International Society for Clinical Biostatistics conference in Munich in 2013. The paper takes the stand of clinician and patient who are in need of a reliable prognostic model for the planning of treatment and patient care during the follow-up after the initial treatment. The paper discusses (i) the need for grouping of data; (ii) the lack of robustness of the Cox model; (iii) the robust approach to repeated measures; and (iv) the robust handling of time-dependent covariates (biomarkers) in dynamic survival analysis.