Meta‐analysis combining parallel and cross‐over clinical trials. II: Binary outcomes

We examine different methods to pool binary outcomes used both in parallel and cross‐over trials. Odds ratio (OR) estimators obtained from joint conditional probabilities in cross‐over trials, such as the Mantel–Haenszel and Peto methods, are compared to an OR estimator using marginal results of cross‐over trials. When there is correlation between the outcomes in the two cross‐over periods, joint conditional ORs differ from marginal ORs and cannot be combined with OR estimates from parallel trials. The marginal OR estimate is independent of the between‐period correlation and it includes a correction for cross‐over correlation in the variance estimate. As its computation is similar in cross‐over and parallel trials, it is the method of choice to pool results from parallel and cross‐over trials in a combined design meta‐analysis. Copyright © 2002 John Wiley & Sons, Ltd.