Hierarchy of evidence

Original Editors -Andeela Hafeez

Top Contributors - Andeela Hafeez, Shaimaa Eldib and Kim Jackson  

Hierarchy Of Evidence:[1]



Systematic Review:

a systematic review is a form of research that provides a summary of medical reports on a specific clinical question, using explicit methods to search, critically appraise, and synthesise the world literature systematically. It is particularly useful in bringing together a number of separately conducted studies, sometimes with conflicting findings, and synthesising their results. By providing in a clear explicit fashion a summary of all the studies addressing a specific clinical question, systematic reviews allow us to take account of the whole range of relevant findings from research on a particular topic, and not just the results of one or two studies.They can be used to establish whether scientific findings are reliable and generalised across populations, settings, and treatment variations, or whether findings vary significantly by particular subgroups.


Following a systematic review, data from individual studies may be united quantitatively and reanalysed using established statistical methods. This technique is called a meta-analysis. The justification for a meta-analysis is that, by combining the samples of the individual studies, the overall sample size is increased, thereby improving the statistical power of the analysis as well as the precision of the estimates of treatment effects.

Randomized Controlled Study:

An experimental design used for testing the effectiveness of a new medication or a new therapeutic procedure. [2]Individuals are assigned randomly to a treatment group (experimental therapy) and a control group (placebo or standard therapy) and the outcomes are compared.


Cohort Study

Analytical study in which a group having one or more similar characteristics (such as habit of smoking or a particular disease) is closely monitored over time simultaneously with another group (whose member do not smoke or are free from the disease).[3]


Case-Control Study:

a non-experimental research design using an epidemiologic approach in which previous cases of the condition are used in lieu of new information gathered from a randomized population.

A group of patients with a particular disease or disorder, such as myocardial infarction, is compared with a control group of persons who have not had that medical problem.

The two groups, matched for age, sex, and other personal data, are examined to determine which possible factor (e.g., cigarette smoking, coffee drinking) may account for the increased disease incidence in the case group.[2]


Case Report:

In medicine, a case report is a detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient. Case reports may contain a demographic profile of the patient but usually describe an unusual or novel occurrence.


an article in a newspaper or other publication presenting the opinion of the publisher, editor,  or editors.


  1. http://www.indianjurol.com/article.asp?issn=0970-1591;year=2011;volume=27;issue=4;spage=536;epage=542;aulast=Mazel
  2. 2.0 2.1 http://library.downstate.edu/EBM2/2200.htm
  3. http://library.downstate.edu/EBM2/2400.htm sunny downstate EBM medical center