Systematic reviews and meta-analyses are at the top of the 'evidence hierarchy' when assessing the effectiveness of health interventions. As such, they are important sources of synthesized information for decision-makers including consumers, clinicians, funders, payers, regulators, and researchers. The main reasons for undertaking systematic reviews and meta-analyses are to minimize bias and to maximize data by collating all the relevant, available evidence on a particular topic. In order to correctly inform decision-makers, but not mislead them, a number of key methodological conditions need to be met when undertaking these types of analysis. In this article we first review the history of systematic reviews and meta-analyses and then outline those conditions that may lead to the correct, or incorrect, use of these types of study. Also, new variations on standard systematic review methods are explored, with the pros and cons of each outlined.
Keywords: Evidence synthesis; Evidence-based healthcare; Meta-analysis; Systematic review.
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