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The use of baseline covariates in cross-over studies

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If you have a question about this talk, please contact Michael Sweeting.

In many settings, cross-over trials that have within-period baseline measurements are analysed wrongly . A `conventional’ analysis of covariance in this setting uses each baseline as a covariate for the following outcome variable in the same period, but not for any other outcome. If used with random subject effects such an analysis leads to biased treatment comparisons; this is an example of cross-level bias. Using a postulated covariance structure that reflects the symmetry of the cross-over setting, such bias can be quantified and, at the same time, potential gains and losses in efficiency through the use of the baselines can be investigated. Alternative methods of analysis are described that avoid the cross-level bias. The development is illustrated with two example trials, one balanced and orthogonal, and one highly unbalanced and non-orthogonal.

This talk is part of the MRC Biostatistics Unit Seminars series.

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