Hierarchy of evidence

Hierarchy Of Evidence:

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.

Meta Analysis:

Following a systematic review, data from individual studies may be united quantitatively and reanalysed using established statistical methods. This technique is called 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.
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).