The EBM pyramid displays information as a hierarchy of evidence.
Moving up the pyramid the amount of available literature decreases, but its relevance to the clinical setting increases.
Fig 1: 5S
Fig 2: 6S
Levels of evidence are determined by the type of study design.
Levels of evidence range from Level I to Level IV, with Level I being highest in reliability.
For example: Systematic review (Level I), Randomised controlled trials (RCTs) (Level II), Cochrane review (‘gold standard’).
Grey literature is "that which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers," according to the Luxembourg Convention.(ICGL Luxembourg definition, 1997, Expanded in New York, 2004).
This category broadly includes reports, theses and dissertations, conference proceedings, standards, technical documentation, datasets, preprints, web content, and government documents.
Primary (unfiltered) resources provide evidence concerning a topic under investigation. These include the major medical databases that provide access to primary studies and peer-reviewed journals. Use critical appraisal tools to evaluate studies.
Secondary (filtered) resources include summaries of primary studies that appraise the quality of studies and often make recommendations for practice. Systematic reviews, Meta-analyses and Clinical practice guidelines fall under this category.
Clinical practice guidelines: