title: Meta-analysis combining parallel and cross-over clinical trials. I: Continuous outcomes.
abstract: Among clinical trials assessing a given treatment, often parallel and cross-over designs are used together. In the first paper of a series of three, we explore two methods to pool continuous outcomes in a meta-analysis combining parallel and cross-over trial designs: the weighted mean difference (WMD) and the standardized weighted mean difference (SWMD). The combined design meta-analytic formulae are based on a weighted average of the two design treatment estimates. A random effects model can be implemented. Both WMD and SWMD can be used, the choice of the method is determined by the type of outcomes obtained in the trials. Compared to the number of included subjects, the relative weight of the cross-over design is large in combined-design meta-analysis. Differences in the weight estimation between WMD and SWMD can also accentuate the relative weight of cross-over trials, which must be considered a case of design-specific bias.
authors.affiliation: Medical Statistics Unit, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1 7HT, UK. francoiscurtin@compuserve.com
authors.forename: François
authors.initials: F
authors.lastname: Curtin
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Altman
authors.forename: Diana
authors.initials: D
authors.lastname: Elbourne
mesh_terms: D001794:Blood Pressure / Q000187:drug effects; D002986:Clinical Trials as Topic / Q000379:methods*; D018592:Cross-Over Studies; D006801:Humans; D015201:Meta-Analysis as Topic; D011188:Potassium / Q000627:therapeutic use; D013223:Statistics as Topic / Q000379:methods*
chemical_list: D011188:Potassium