Hierarchy of Evidence
"The article describes the hierarchy of research design in evidence-based sports medicine. These designs range from descriptive narratives to experimental clinical trials. Research designs include randomized controlled trials, prospective cohort study, outcomes study, case-control study, cross-sectional study, case series and case study."
McKeon, Patrick, Jennifer M. Medina, and Jay Hertel. 2006. Hierarchy of Research Design in Evidence-Based Sports Medicine. Athletic Therapy Today 11 (4): 42–45.
"The article looks at rating evidence levels in sports medicine research. Evidence sources range from clinical observations to randomized controlled trials. Evidence levels range from 1 to 5; 1 being the highest quality and 5 being the lowest. The first level represents unbiased information from clinical studies. Each evidence level can be subdivided into smaller categories. Clinicians should assess evidence based on quality, quantity, and consistency. Results must be statistically significant or nonsignificant with little variation."
Rating the Levels of Evidence in Sports-Medicine Research. 2006. Athletic Therapy Today 11 (5): 38–41.
Meta-analysis and Systematic Reviews
“The term “systematic” refers to the strict approach (clear set of rules) used for identifying relevant studies; 11,15 which includes the use of an accurate search strategy in order to identify all studies addressing a specific topic, the establishment of clear inclusion/exclusion criteria and a well-defined methodological analysis of the selected studies... A systematic review can be concluded in a qualitative way by discussing, comparing and tabulating the results of the various studies, or by statistically analysing the results from independent studies: therefore conducting a meta-analysis… By combining individual studies it is possible to provide a single and more precise estimate of the treatment effects.” (p.495)
Impellizzeri F, Bizzini M. Systematic Review and Meta-Analysis: A Primer. International Journal Of Sports Physical Therapy 7, no.5 (2012): 493-503.
Hierarchy of evidence for clinical questions related to therapy, prevention, etiology or harm.
Always start an EBP search looking for the highest level of evidence. If a meta-analysis is not available on the topic, look next for systematic reviews without statistical synthesis, next for randomized control trials, next for cohort studies, next for case control studies, etc...
For more detailed information about the levels of evidence see the Oxford Centre for Evidence-based Medicine - Levels of Evidence (March 2009).