The Cochrane Skin Group recommends that the most reliable evidence comes from well designed randomised controlled trials, and that these should form the basis of its systematic reviews of interventions.
Therefore, the reviews from the Cochrane Skin Group are normally based on randomised trials only. It is however important to also look at all papers that are classed as controlled clinical trials as the method of allocation may be random but may not have been clearly stated.
Other forms of evidence such as case control studies are occasionally used when discussing issues such as adverse events. "Quasi-randomised" trials, where allocation is by non-random methods such as alternation, or is based on characteristics such as date of birth, name or case number, should not be included.
Authors assess each article to determine if it has met the predefined inclusion criteria for the review. These criteria include both the study design and the characteristics of the main outcomes under study. We recommend that the selection of studies for inclusion in reviews is independently carried out by more than one author. Differences between selections are then resolved through discussion and by consensus. Pilot testing of study selection on a subset of the trial reports should normally be carried out.
We do not consider blinding of authors to authorship of the trial reports to be necessary.
For more information please see the Cochrane Handbook www.cochrane-handbook.org.