Abstract:
We present a simple semiparametric model for tting subject-speci c curves for longitudinal data. Individual curves are modelled as penalized splines with random coe cients. This model has a mixed model representation, and it is easily implemented in standard statistical software. We conduct an analysis of the long-term e ect of radiation therapy on the height of children su ering from acute lymphoblastic leukaemia using penalized splines in the framework of semiparametric mixed e ects models. The analysis revealed signi cant di erences between therapies and showed that the growth rate of girls in the study cannot be fully explained by the group-average curve and that individual curves are necessary to re ect the individual response to treatment. We also show how to implement these models in S-PLUS and R in the appendi
