The systematic review of health care evidence: methods, issues, and trends.

The systematic review is a key component to the evidence based health care cycle. There are two main types of systematic reviews: qualitative and quantitative. Systematic reviews bring together large amounts of information that can help support individual patient decision, inform guidelines, policy and primary research. The basic steps for each type of systematic review are the same; however, differences occur in the tools used to appraise the included studies and the method of synthesis. Over the years, many different systems have been used to grade the quality (level) of evidence and the strength of recommendations, which has meant that the same evidence and recommendation could be graded differently according to the system used at the time.