evidence is judged to be of equal value,
that is, there are hierarchies of research
design that are evaluated to have different
strengths, different levels of value in
the decision making process. See the two
charts below – one graphically represented,
one textually to help understand the
concepts important to critical appraisal,
assessment, and evaluation of research.
The Evidence Pyramid
[Source: Source: SUNY Downstate Medical Center.
Medical Research Library of Brooklyn. Evidence
Based Medicine Course. A Guide to Research
Methods: The Evidence Pyramid: http://library.downstate.edu/EBM2/2100.htm]
For a definition of the different types of research methodology, i.e.
systematic review, randomized controlled trial, and others, visit the
Medical Research Library of Brooklyn's Evidence Based Medicine tutorial.
Levels of Evidence
- Category I: Evidence
from at least one properly
randomized controlled trial.
- Category II-1: Evidence from well-designed
controlled trials without randomization.
- Category II-2: Evidence from well-designed
cohort or case-control analytic
studies, preferably from more than one
center or research group.
- Category II-3: Evidence from multiple
times series with or without
intervention or dramatic results in uncontrolled
experiments such as the results
of the introduction of penicillin treatment
in the 1940s.
- Category III: Opinions of respected
authorities, based on clinical
experience, descriptive studies and case
reports, or reports of expert committees.
[Source: Harris, R.P. et
al. (2001). Current methods of the U.S. Preventive
Services Task Force: a review of the process.
American Journal of Preventive Medicine. April
20 (3 Supplement): 21-35.]