A systematic review is:

A summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies, and that uses appropriate statistical techniques to combine these valid studies. [2]

Systematic reviews provide the strongest type of evidence, as the authors attempt to find all research on a topic, published and unpublished. The authors then combine the research into a single analysis. Keep in mind that systematic reviews are different than review articles. While systematic reviews are conducted to answer a specific clinical foreground question, review articles provide a broad overview on a topic to answer background questions. Another difference is that the literature search for review articles does not attempt to find all existing knowledge on a topic.

Meta-Analysis

A meta-analysis is a particular type of systematic review that attempts to combine and summarize quantitative data from multiple studies using sophisticated statistical methodology. Such a strategy strengthens evidence as it makes the small sample size of individual studies much larger, giving the results more statistical power and, therefore, more credibility than the individual studies. Meta-analyses are not comprehensive, as only compatible data may be combined into a larger data set.

Authors should clearly specify the criteria for inclusion or exclusion of individual studies somewhere in a systematic review or meta-analysis.

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