Grading the evidence: the core of EBD.

Disasters surrounding medical drugs and devices that led to public outcries for regulation have led to both legislation and the recognition that all sources of evidence are not equal in terms of reliability. Randomized controlled trials provide more reliable evidence than case-series, and human studies provide more reliable evidence than animal studies. In evidence-based medicine, different hierarchies have been created to grade the reliability of evidence. This report provides a brief review of the evidence-pyramid.