Analysing repeated measurements data: a practical comparison of methods.
A variety of methods are available for analysing repeated measurements data where the outcome is continuous. However, there is little information on how established methods, such as summary statistics and repeated measures analysis of variance (RMAOV), compare in practice with methods that have become available to applied statisticians more recently, such as marginal models (based on generalized estimating equation methodology) and multilevel models (that is, hierarchical random effects models). The aim of this paper is to exemplify the use of these methods, and directly compare their results by application to a clinical trial data set. The focus is on practical aspects rather than technical issues. The data considered were taken from a clinical trial of treatments for asthma in 240 children, in which a baseline and four post-randomization measurements of outcomes were taken. The simplicity of the method of summary statistics using the post-randomization mean of observations provided a useful initial analysis. However, fixed time effects or treatment-time interactions cannot be included in such an analysis, and choice of appropriate weighting when there is substantial missing data is problematic. RMAOV, marginal models and multilevel models generally provided similar estimates and standard errors for the treatment effects, although in one example with a relatively complex variance structure the marginal model produced less efficient estimates. Two advantages of multilevel models are that they provide direct estimates of variance components which are often of interest in their own right, and that they can be naturally extended to handle multivariate outcomes.
Department of Medical Statistics and Evaluation, Imperial College School of Medicine, Du Cane Road, London W12 0NN, U.K. romar@rpms.ac.uk
R Z
RZ
Omar
E M
EM
Wright
R M
RM
Turner
S G
SG
Thompson
D000293:Adolescent; D000704:Analysis of Variance; D001249:Asthma / Q000188:drug therapy; D001507:Beclomethasone / Q000627:therapeutic use; D002648:Child; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D005938:Glucocorticoids / Q000627:therapeutic use; D006801:Humans; D015233:Models, Statistical; D015337:Multicenter Studies as Topic / Q000706:statistics & numerical data; D015999:Multivariate Analysis; D010366:Peak Expiratory Flow Rate / Q000187:drug effects; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data
D005938:Glucocorticoids; D001507:Beclomethasone