Objectives To assess how often stratified randomisation is used, whether analysis adjusted
for all balancing variables, and whether the method of randomisation was adequately …

Background Selection bias occurs when recruiters selectively enrol patients into the trial
based on what the next treatment allocation is likely to be. This can occur even if appropriate …

Background Adjustment for prognostic covariates can lead to increased power in the
analysis of randomized trials. However, adjusted analyses are not often performed in …

Many clinical trials restrict randomisation using stratified blocks or minimisation to balance
prognostic factors across treatment groups. It is widely acknowledged in the statistical …

Background It is often desirable to account for centre-effects in the analysis of multicentre
randomised trials, however it is unclear which analysis methods are best in trials with a …

This article reviews three traditional methods for the analysis of multicenter trials with
persons nested within clusters, ie, centers, namely naı̈ve regression (persons as units of …

Power Analysis of Trials with Multilevel Data is a valuable reference for anyone who wants
to perform power calculations on trials with hierarchical data. It provides a thorough …

Background Reporting of absolute risk difference (RD) is recommended for clinical and
epidemiological prospective studies. In analyses of multicenter studies, adjustment for …

Background Recent reviews have shown that while clustering is extremely common in
individually randomised trials (for example, clustering within centre, therapist, or surgeon), it …

In multicentre trials, randomisation is often carried out using permuted blocks stratified by
centre. It has previously been shown that stratification variables used in the randomisation …