"Determining what constitutes the best evidence requires an ability to identify, critique and categorize literature, placing it into a so-called hierarchy of evidence or, rank-order, with randomized controlled trials (RCT's) and meta-analyses of RCT's at the top and uncontrolled studies or opinion at the bottom. This is a necessary first step as the ability to infer a recommendation or establish a grade of recommendation for a treatment or intervention is directly related to the quality of evidence that is available for review. These steps then provide the basis for the development of clinical practice guidelines, to not replace clinical decision making but augment it. There have been a number of systems developed to try to categorize studies into their respective levels of evidence."
Source: B.A. Petrisor, J. Keating, E. Schemitsch. Grading the evidence: Levels of evidence and grades of recommendation, Injury, Volume 37, Issue 4, 2006, Pages 321-327, ISSN 0020-1383, https://doi.org/10.1016/j.injury.2006.02.001.
Source: Merlin, T. , Weston, A. , Tooher, R., (2009). Extending An Evidence Hierarchy To Include Topics Other Than Treatement: Revisting The Australian 'Levels of Evidence'. BMC Medical Research Methodology 2009, 9:34. doi:10.1186/1471-2288-9-34
A general overview of the concept of levels of evidence and how it is applied in the medical field. Source (https://youtu.be/OaOzXEWIXY4)
Provides a more in-depth look at the different levels of evidence as reported in the John Hopkins Hierarchy. ( Source https://youtu.be/u_-lxyFtlN8 )
