The use of baseline covariates in cross-over studies
- đ¤ Speaker: Mike Kenward, London School of Hygiene and Tropical Medicine
- đ Date & Time: Tuesday 19 May 2009, 14:30 - 15:30
- đ Venue: Large Seminar Room, 1st Floor, Institute of Public Health, University Forvie Site, Robinson Way, Cambridge
Abstract
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.
Series This talk is part of the MRC Biostatistics Unit Seminars series.
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Mike Kenward, London School of Hygiene and Tropical Medicine
Tuesday 19 May 2009, 14:30-15:30