A Systematic Review is a summary that attempts to address a focused clinical question using methods designed to reduce the likelihood of bias. Systematic reviews provide a summary of the available literature using explicit methods to systematically search, critically appraise, and synthesize the world literature on a specific issue" (Straus et al, 2005). A meta-analysis is a type of systematic review that uses statistical, quantitative methods to describe the results.
Unlike simple review articles, a systematic review is based on a systematic review of the evidence and requires an exhaustive search of the literature. Review articles are more narrative and, while a good way to start your research or learn about a topic, do not follow the strict methodology demanded of a systematic review. A systematic review uses numerical or cross-study analysis to synthesize the findings of original studies and are more clinically based. Systematic reviews must clearly state why the research is being done and what methods were used to find the primary studies. These methods must be described so that the search process can be replicated.
Systematic reviews often require a significant time investment. Allen and Olkin, in 1999, reported 1139 hours were required for a review, on average, though the time investment was often dependent on the number of citations retrieved for a search.
The table below, reproduced from Guyatt et al., 2008, illustrates the differences between traditional narrative reviews and systematic reviews.
| Characteristic | Narrative Review | Systematic Review |
|---|---|---|
| Clinical Question | Seldom reported, or addresses several general questions | Focused question specifying population, intervention or exposure, and outcome |
| Search for primary articles | Seldom reported; if reported not comprehensive | Comprehensive search of several evidence sources |
| Selection of primary articles | Seldom reported; if reported, often biased sample of studies | Explicit inclusion and exclusion criteria for primary studies |
| Evaluation of quality of primary articles | Seldom reported; if reported, not usually systematic | Methodologic quality of primary articles is assessed |
| Summary of results of primary studies | Usually qualitative nonsystematic summary | Synthesis is systematic (qualitative or quantitative; if quantitative, this is often referred to as meta-analysis) |
