The evidence pyramid is used to illustrate the evolution of the literature.
As you move up the pyramid the amount of available literature decreases, but increases in its relevance to the clinical setting.
The base of the pyramid is where information usually starts with an idea or laboratory research. As these ideas turn into therapies and diagnostic tools they are tested with laboratory models, then in animals, and finally in humans. The human testing may begin with volunteers and go through several phases of clinical trials before the drug or diagnostic tool can be authorized for use within the general population. Randomized controlled trials are then done to further test the effectiveness and efficacy of a drug or therapy.
Levels of evidence provide a ranking system used in evidence based practice to describe the strengths of results measured in a clinical trial or research study.
See Levels of Evidence for more information.