"A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question" (The Cochrane Library, "What Is A Systematic Review").
Meta analysis is "a statistical synthesis of the numerical results of several trials which all address the same question" (Greenhalgh, 2010, p.121).
Both types of reviews provide a very high level of evidence.
The Cochrane Library. (n.d.). About Cochrane systematic reviews and protocols. Retrieved July 18, 2011 from http://www.thecochranelibrary.com/view/0/AboutCochraneSystematicReviews.html
Greenhalgh, T. (2010). How to read a paper: The basics of evidence-based medicine. Chichester, United Kingdom: Wiley-Blackwell.
PubMed is a free resource provided by the U.S. National Library of Medicine. It includes over 20 million citations from the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and preclinical sciences. There is a link to PubMed on the Library Article Databases web page.
Follow the steps below to find systematic reviews and meta analysis articles.
Greenhalgh, T. (1997). Education and debate. How to read a paper: papers that summarise other papers (systematic reviews and meta-analyses)... ninth in a series of 10 articles. BMJ: British Medical Journal (International Edition), 315(7109), 672-675. Retrieved from http://www.bmj.com/