Evidence from crossover trials: empirical evaluation and comparison against parallel arm trials.

Background: We aimed to evaluate empirically how crossover trial results are analysed in meta-analyses of randomized evidence and whether their results agree with parallel arm studies on the same questions.

Methods: We used a systematic sample of Cochrane meta-analyses including crossover trials. We evaluated the methods of analysis for crossover results and compared the concordance of the estimated effect sizes in crossover vs parallel arm trials.