title: Exploratory analysis of longitudinal trials with staggered intervention times.
abstract: 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.
authors.affiliation: Department of Mathematics and Statistics, Lancaster University, LA1 4YF, Lancaster, UK. i.pereirasilvacunhasousa@lancaster.ac.uk
authors.forename: Inês
authors.initials: I
authors.lastname: Sousa
authors.forename: Amanda G
authors.initials: AG
authors.lastname: Chetwynd
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Diggle
mesh_terms: D000465:Algorithms; D001699:Biometry; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D004646:Emphysema / Q000503:physiopathology / Q000601:surgery; D005541:Forced Expiratory Volume; D006801:Humans; D008137:Longitudinal Studies; D018709:Statistics, Nonparametric