Simple fitting of subject-specific curves for longitudinal data

M. Durbán, J. Harezlak, M. P. Wand, R. J. Carroll

Research output: Contribution to journalArticle

107 Scopus citations


We present a simple semiparametric model for fitting subject-specific curves for longitudinal data. Individual curves are modelled as penalized splines with random coefficients. This model has a mixed model representation, and it is easily implemented in standard statistical software. We conduct an analysis of the long-term effect of radiation therapy on the height of children suffering from acute lymphoblastic leukaemia using penalized splines in the framework of semiparametric mixed effects models. The analysis revealed significant differences 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 reflect the individual response to treatment. We also show how to implement these models in S-PLUS and R in the appendix.

Original languageEnglish (US)
Pages (from-to)1153-1167
Number of pages15
JournalStatistics in Medicine
Issue number8
StatePublished - Apr 30 2005
Externally publishedYes


  • Acute lymphoblastic leukaemia
  • Linear mixed models
  • Penalized splines
  • Restricted likelihood ratio tests

ASJC Scopus subject areas

  • Epidemiology
  • Statistics and Probability

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