Exploratory analysis of longitudinal trials with staggered intervention times

Inês Sousa, Amanda G. Chetwynd, Peter J. Diggle

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Longitudinal trials involving surgical interventions commonly have subject-specific intervention times, due to constraints on the availability of surgeons and operating theatres. Moreover, the intervention often effects a discontinuous change in the mean response. We propose a nonparametric estimator for the mean response profile of longitudinal data with staggered intervention times and a discontinuity at the times of intervention, as an exploratory tool to assist the formulation of a suitable parametric model. We use an adaptation of the standard generalized additive model algorithm for estimation, with smoothing constants chosen by a cross-validation criterion. We illustrate the method using longitudinal data from a trial to assess the effect of lung resection surgery in the treatment of emphysema patients.

Original languageEnglish (US)
Pages (from-to)479-485
Number of pages7
Issue number3
StatePublished - Jul 2005
Externally publishedYes


  • Back-fitting algorithm
  • Cross-validation
  • Exploratory analysis
  • Longitudinal trials
  • Lung resection surgery
  • Nonparametric estimator

ASJC Scopus subject areas

  • Medicine(all)
  • Statistics and Probability
  • Statistics, Probability and Uncertainty


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