Sample size definition provides important information, allowing the groundwork for transparent reporting. The sample predefinition allows the trial to be large enough to be able to address the question that is being asked.

The aim of the present study is to assess, in all the randomized controlled trials (RCT) included in the Cochrane Hepato-Biliary Group (CHBG) systematic reviews, the quality of reporting sample size the accuracy of the calculations, the accuracy of the a priori assumptions and the effect on the agreement with pooled results in meta-analyses.

The investigators aim to answers to these questions

Questions

• How large a proportion of recent hepato-biliary RCTs does report an adequate sample size estimation?
• Primary outcome is clearly defined ? and clinical meaningful ?
• Is the sample size calculation based on the primary outcome ?
• Does the predicted control event rate coincide with the actual one?
• What is the predicted intervention effect?
• Are confidence intervals of primary outcome results reported? Is there evidence of difference between the two arms?
• Is the effect size so large (> 50%) to suggest post hoc definition ?
• What is the accepted error alpha and beta?
• How many study do not comply with the usual rule of alpha = 5% beta = 20%?
• Do trials with planned sample size do better than those without ? Is the overlap between CI results less frequent ? Are their results more frequently "statistical" significant ?
• Do trials with planned sample more frequently agree with pooled results in meta-analysis ?
• Has the protocol been published in a public register before inclusion of participant?
• How often is intention-to-treat analyses employed as primary analysis?
• How often is the trial results resting upon subgroup analysis?

Methods:

All the randomized clinical trials included in a systematic review of the Cochrane Hepato-biliary group (according to my search 272) were detected and retrieved. Only two arm, parallel group superiority randomised controlled trials with a single primary outcome.

The investigators excluded reports for which the study design was factorial, cluster, or crossover For all selected articles, the investigators systematically retrieved and assessed the full published report of the trial, any extra material or appendices available online, the study design article, if cited, and the details of online registration of the trial, if mentioned. A standardised data collection form was generated on the basis of a review of the literature and a priori discussion and tested by the research team.

Inclusion Criteria:

• Two arms, parallel group superiority randomised controlled trials with a single primary outcome,

Exclusion Criteria:

• Reports for which the study design was factorial, cluster, or crossover

Randomized clinical trials included in systematic reviews of the hepato-biliary Group of the Cochrane Collaboration