This is the program for the 2010 Joint Statistical Meetings in Vancouver, British Columbia.

Abstract Details

Activity Number: 329
Type: Topic Contributed
Date/Time: Tuesday, August 3, 2010 : 10:30 AM to 12:20 PM
Sponsor: Biopharmaceutical Section
Abstract - #306355
Title: The Use of Baseline Covariates in Cross-Over Studies
Author(s): Byron Jones*+ and Michael G. Kenward and James Henry Roger
Companies: Pfizer Inc. and London School of Hygiene and Tropical Medicine and GlaxoSmithKline
Address: Ramsgate Road, Sandwich, International, CT13 9NJ, UK
Keywords: Cross-over ; Baseline ; Cross-level bias ; Random effects
Abstract:

Cross-over trials that have within-period baseline measurements are often analysed incorrectly. 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. This is valid in an analysis where subject is treated as a fixed effect. However, when 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, we quantify such bias and, at the same time, investigate potential gains and losses in efficiency through the use of the baselines. We describe alternative methods of analysis that avoid such cross-level bias.


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