Randomized clinical trials with a pre- and a post-treatment measurement: repeated measures versus ANCOVA models

B. Winkens*, G.J.P. van Breukelen, H.J.A. Schouten, M.P.F. Berger

*Corresponding author for this work

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Repeated measures (RM) and ANCOVA models are compared with respect to treatment effect estimation in randomized clinical trials with a pre- and a post-treatment measure. The covariance matrices of repeated measures are assumed to be I) homogeneous or II) heterogeneous across groups. In situation I, ANCOVA is preferred to RM, because the estimated variance of the treatment effect estimator is unbiased for ANCOVA and biased downwards for RM. In situation II, RM with Kenward and Roger's adjustment is preferred to ANCOVA, because the ANCOVA variance estimator does not correct for unknown pre-treatment expectation. The results are illustrated with an example.
Original languageEnglish
Pages (from-to)713-719
JournalContemporary Clinical Trials
Issue number6
Publication statusPublished - 1 Jan 2007

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