There is increasing interest in the medical world in the possibility of tailoring treatment to the individual patient. Statistically, the relevant task is to identify interactions between covariates and treatments, such that the patient’s value of a given covariate influences how strongly (or...

Assessing the instability of a multivariable model is important but is rarely done in practice. Model instability occurs when selected predictors--and for multivariable fractional polynomial modeling, selected functions of continuous predictors--are sensitive to small changes in the data....