Cochrane Database of Systematic Reviews contains full-text articles, as well as protocols focusing on the effects of healthcare. The reviews are highly structured and systematic, with evidence included or excluded on the basis of explicit quality criteria, to minimize bias.
Data is evidence-based medicine and is often combined statistically (with meta-analysis) to increase the power of the findings of numerous studies, each too small to produce reliable results individually. Now included in the 4,800-plus records are 22 reviews which formerly made up the Cochrane Database of Methodology Reviews. This database is updated quarterly.
These journals may be useful.
This is not a comprehensive list, but a set of starting points. In a library database, you can search by Journal Name in conjunction with your other search terms.