Systematic Reviews

What is a systematic review?

• According to the Cochrane Handbook of Systematic Reviews, a systematic review is a review that seeks "to collate evidence that fits pre-specified eligibility criteria in order to answer a specific research question."
• In other words, a systematic review attempts to collect and analyze all papers written that answer a specific research question. Researchers find and select these papers based on specified inclusion criteria.
• Systematic reviews also aim to minimize bias by "using explicit, systematic methods documented in advance with a protocol."
  • In other words, systematic reviews must include a record of the search strategy used to find the relevant papers and, ideally, should also have a protocol written before any searching is begun.

Common Elements of a Systematic Review

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 specific research question (often in the PICO format), along with clearly stated objectives for the review and pre-defined inclusion and exclusion criteria for the studies.
• A reproducible, comprehensive search strategy. 
• A meta-analysis of the selected papers.

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:

• the clinical question 
• inclusion/exclusion criteria
• types of clinical studies to be included
• search strategy
• and much more

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.