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- Title
Methods to assess an exercise intervention trial based on 3-level functional data.
- Authors
HAOCHENG LI; KEADLE, SARAH KOZEY; STAUDENMAYER, JOHN; ASSAAD, HOUSSEIN; HUANG, JIANHUA Z.; CARROLL, RAYMOND J.; Li, Haocheng; Kozey Keadle, Sarah
- Abstract
Motivated by data recording the effects of an exercise intervention on subjects' physical activity over time, we develop a model to assess the effects of a treatment when the data are functional with 3 levels (subjects, weeks and days in our application) and possibly incomplete. We develop a model with 3-level mean structure effects, all stratified by treatment and subject random effects, including a general subject effect and nested effects for the 3 levels. The mean and random structures are specified as smooth curves measured at various time points. The association structure of the 3-level data is induced through the random curves, which are summarized using a few important principal components. We use penalized splines to model the mean curves and the principal component curves, and cast the proposed model into a mixed effects model framework for model fitting, prediction and inference. We develop an algorithm to fit the model iteratively with the Expectation/Conditional Maximization Either (ECME) version of the EM algorithm and eigenvalue decompositions. Selection of the number of principal components and handling incomplete data issues are incorporated into the algorithm. The performance of the Wald-type hypothesis test is also discussed. The method is applied to the physical activity data and evaluated empirically by a simulation study.
- Subjects
PHYSICAL activity; BIOMETRY; CLINICAL trials; RANDOM effects model; DATA recorders &; recording; EXPECTATION-maximization algorithms; ALGORITHMS; EXERCISE therapy; EXPERIMENTAL design; HEALTH outcome assessment; RESEARCH funding; STATISTICAL models
- Publication
Biostatistics, 2015, Vol 16, Issue 4, p754
- ISSN
1465-4644
- Publication type
journal article
- DOI
10.1093/biostatistics/kxv015