Answered By: Rebecca Eyres
Last Updated: Nov 27, 2020     Views: 8

Research output comes in all shapes and sizes, and can vary in quality, some more robust and rigorous than others.

An evidence hierarchy, often referred to in evidence based medicine, provides a top-down scale whereby you first search for a recent well-conducted systematic review and if that is not available, then move down to the next level of evidence to answer your question.

Evidence further down the scale may have a greater risk of bias.


Higher Quality Evidence

(Lower risk of bias)

Systematic reviews and meta-analysis of randomised controlled trials
  Randomised controlled trials
  Cohort studies
  Case-controlled studies
  Cross-sectional studies, surveys
  Case reports, case studies


Mechanistic studies

Lower Quality of Evidence


(Higher risk of bias)

Editorials, expert opinion