The reviews are presented in two types: Cochrane Methodology Reviews are full-text systematic reviews of methodological studies. The reviews are both highly structured and systematic. Evidence from methodological research is included or excluded on the basis of explicit quality criteria, thus minimizing bias. Each review covers a specific and well-defined area of methodology. Data from studies are often combined statistically to increase the power of the findings of numerous studies, which on their own may be too small to produce reliable results. In such cases, the review may also include graphs presenting the data from each individual study. Protocols provide place-markers for reviews, which are currently being written. They summarize the background and the rationale of the review.