The EVIDENCE PYRAMID is often used to illustrate the development of evidence. At the base of the pyramid is animal research and laboratory studies - this is where ideas are first developed. As you progress up the pyramid the amount of information available decreases in volume, but increases in relevance to the clinical setting.
Meta Analysis - systematic review that uses quantitative methods to synthesize and summarize the results.
Systematic Review - summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate statistical techniques to combine these valid studies.
Randomised Controlled Trial - Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest.
Cohort Study - Involves identification of two groups (cohorts) of patients, one which received the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
Case Control Study - study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.
Case Series - report on a series of patients with an outcome of interest. No control group is involved. (Definitions from CEBM)
The evidence pyramid above 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.