While the Cochrane methodology to systematic reviews is one of the most common, there is no one absolute standard for systematic reviews. However, there are common elements that all quality systematic reviews should have.
A true systematic review requires researchers to find essentially all information pertinent to a specific clinical question, then compile that data and draw conclusions. A protocol is usually written that spells out:
A meta-analysis takes it a step further. A biostatistician compiles and reports the results, often in a forest plot format.
"Systematic reviews identify, select, assess, and synthesize the findings of similar but separate studies and can help clarify what is known and not known about the potential benefits and harms of drugs, devices, and other healthcare services.
"Systematic reviews can be helpful for clinicians who want to integrate research findings into their daily practices, for patients to make well-informed choices about their own care, and for professional medical societies and other organizations that develop clinical practice guidelines."
Institute of Medicine.(March 2011). Report Briefs: Finding what works in healthcare standards for systematic reviews.
A good source for an overview is Finding What Works in Health Care, Standards for Systematic Reviews, published by Institute of Medicine (US) Committee on Standards for Systematic Reviews of Comparative Effectiveness Research.