| Titre : | Evidence from crossover trials : empirical evaluation and comparison against parallel arm trials. (2007) |
| Auteurs : | Dimitrios-N LATHYRIS ; John-Pa IOANNIDIS ; Thomas-A TRILCALMOS ; Tufts University. School of Medicine. Department of Medicine. Institute for Clinical Research and Health Policy Studies. Boston. MA. USA ; University of loannina. School of Medicine. Department of Hygiene and Epidemiology. Clinical Trials and Evidence-Based Medicine Unit. Ioannina. GRC |
| Type de document : | Article |
| Dans : | International journal of epidemiology (vol. 36, n° 2, 2007) |
| Pagination : | 422-430 |
| Langues: | Anglais |
| Mots-clés : | Essai comparatif ; Essai thérapeutique ; Evaluation ; Etude comparée |
| Résumé : | [BDSP. Notice produite par INIST-CNRS gR0xrODm. Diffusion soumise à autorisation]. 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. Results : Of 334 screened reviews, 62 had crossover trials. Of those, 33 meta-analyses performed quantitative syntheses involving two-arm two-period crossover trials. There was large variability on how these trials were analysed ; only one of the 33 meta-analyses stated that they used the data from both the first and second period with an appropriate paired approach. Nine meta-analyses used the first period data only and 14 gave no information at all on what they had done. Twenty-eight meta-analyses had both crossover n=137, sample size n=7162) and parallel arm (n=132, sample size n=11 398) trials. Effect sizes correlated well with the two types of designs (p=0.72). Differences on whether the effect had a P<0.05 or not were common due to limited sample sizes. The summary relative odds ratio for parallel arm vs crossover designs for favourable outcomes was 0.87 (95% CI, 0.74-1.02). Conclusions : Crossover designs may contribute evidence in a fifth of systematic reviews, but few meta-analyses make use of their full data. The results of crossover trials tend to agree with those of parallel arm trials, although there was a trend for more conservative treatment effect estimates in parallel arm trials. |
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