The levels of evidence and grades of recommendation were developed in order to help
people answer the following questions in a systematic way:
1. How strong is the evidence that a treatment works (or is harmful, or that a
diagnostic test is accurate, etc.)?
2. Should I use the treatment (or diagnostic test, etc.)?
Since the original levels of evidence were published 3 decades ago (1979; Sackett 1986),
other sometimes conflicting versions have cropped up (Atkins, Briss et al. 2005). The
OCEBM levels have the advantage that they offer levels of evidence for therapy,
prognosis, diagnosis, differential diagnosis, and economic analysis all in a single table.
The table is available in word, rtf, pdf, and html versions.
Although the levels are a useful tool as they stand, they are not helpful in some cases,
especially where the effect sizes are dramatic (Glasziou, Chalmers et al. 2007). Over the
next few months, the OCEBM will undertake a major revision of our levels of evidence. If
you have any useful input or are interested in this project please join our mailing list or
email Jeremy Howick.
References
(1979). "The periodic health examination. Canadian Task Force on the Periodic Health
Examination." Can Med Assoc J 121(9): 1193-254.
Atkins, D., P. A. Briss, M. Eccles, S. Flottorp, G. H. Guyatt, R. T. Harbour, et al. (2005).
"Systems for grading the quality of evidence and the strength of
recommendations II: pilot study of a new system." BMC Health Serv Res 5(1): 25.
Glasziou, P., I. Chalmers, M. Rawlins and P. McCulloch (2007). "When are randomised
trials unnecessary? Picking signal from noise." BMJ 334(7589): 349-51.
Sackett, D. L. (1986). "Rules of evidence and clinical recommendations on the use of
antithrombotic agents." Chest 89(2 Suppl): 2S-3S.
These pages are under development
by Jeremy Howick.