What are systematic reviews and why are they important?
Systematic reviews are a special type of journal article that has very strong evidence to back its conclusions. Specficially,
"Systematic reviews exhaustively search for, identify, and summarise the available evidence that addresses a focused clinical question, with particular attention to methodological quality. ... Clinicians can then apply these results to the wide array of patients who do not differ importantly from those enrolled in the summarised studies. Systematic reviews can also inform investigators about the frontier of current research. Thus, both clinicians and researchers should be able to reliably and quickly find valid systematic reviews of the literature." (BMJ. 2005 January 8; 330(7482): 68-73)
Systematic Reviews & Public Health - are they really feasible?
In clinical medicine, the randomized controlled trial (RCT) is most often viewed as providing the highest level of evidence; In some cases, particularly with public health topics, it is not always feasible or ethical to conduct a RCT. However, that does not mean that there is no evidence that can be systematically reviewed. An editorial in the Bulletin of the World Health Organization has a very nice overview of systematic reviews for public heatlh. ( 2009 March; 87(3): 163)
"After all, public health problems require us to draw on complex sets of qualitative as well as quantitative evidence; and some policy interventions have never been subjected to randomized controlled trials (RCTs) but have been evaluated using other approaches; everything from controlled and uncontrolled before-and-after studies, to time series analyses, to qualitative methods."
Systematic reviews grew out of the evidence-based medicine (EBM) movement. To fully understand why the conclusions of systematic reviews carry more weight than other types of reviews and articles, a little background in evicence-based practice (EBP) would help. You can look up the definition of EBM online, for our purposes, a simple definition of EBP is "Evidence-based practice is based on evaluation research that highlights interventions that have been found to be effective."
A key pictorial description of the levels of evidence sources is the pyramid. Of course, the best are at the top and as the picture shows, you have much fewer resource there than a lower level, i.e., Background Info. The following is one example of an evidence pyramid.
For more about Evidence-based Public Health, see the online tutorials:
The Cochrane Library is a collection of resources and instead of searching through all resources, we will use just the Database of Systematic Reviews.
PubMed Clinical Queries targets just those articles found in PubMed that are tagged as systematic reviews. The results include articles published in any journal that is a systematic review as well as Cochrane Reviews.