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Level of Evidence & Strength of Recommendation
Traditional Clinical Practice Guidelines Lifecycle
Computerized Clinical Practice Guidelines Lifecycle
Computerized Clinical Practice Guidelines Systems Review
SAGE and Guide for “workflow awareness”
1996
Evidence-based Healthcare: How to Make Health Policy and Management Decisions
J.A.Muir Gray, Churchill Livingstone
As CPGs are evidence-based, it is fundamental to grade all the recommendations on the basis of the predictive power of the study designs from which recommendations are obtained. In other words, the grading assigned to a recommendation is related to the likelihood that, if that recommendation is implemented, the predicted outcome will be achieved. This is the reason why good CPGs provide at least the “Level of Evidence” for each provided recommendation.
Several grading systems have been proposed by different organizations and institutions. An example is provided by Scottish Intercollegiate Guidelines Network (SIGN ), [1, 2] SIGN formerly used the levels of evidence developed by the US Agency for Health Care Policy and Research [3] (AHCPR, now the US Agency for Health Research and Quality, AHRQ). However as a number of limitations was becoming apparent in that system, a review was carried out and new levels of evidence and associated grades of recommendation were developed. Following extensive consultation and international peer review, the new grading system was introduced in Autumn 2000. The new grading system is shown in the following table:
LEVEL OF EVIDENCE |
DESCRIPTION |
1++ |
High quality meta analyses, systematic reviews of Randomized Controlled Trials (RCTs), or RCTs with a very low risk of bias |
1+ |
Well conducted meta analyses, systematic reviews of RCTs, or RCTs with a low risk of bias |
1- |
Meta analyses, systematic reviews of RCTs, or RCTs with a high risk of bias |
2++ |
High quality systematic reviews of case-control or cohort studies High quality case-control or cohort studies with a very low risk of confounding, bias, or chance and a high probability that the relationship is causal |
2+ |
Well conducted case control or cohort studies with a low risk of confounding, bias, or chance and a moderate probability that the relationship is causal |
2- |
Case control or cohort studies with a high risk of confounding, bias, or chance and a significant risk that the relationship is not causal |
3 |
Non-analytic studies, e.g. case reports, case series |
4 |
Expert opinion |
From the levels of evidence it is possible to derive the more compact and operative classification: “Grades of Recommendation”:
GRADE OF RECOMMENDATION |
DESCRIPTION |
A |
At least one meta analysis, systematic review, or RCT rated as 1++, and directly applicable to the target population; or A systematic review of RCTs or a body of evidence consisting principally of studies rated as 1+, directly applicable to the target population, and demonstrating overall consistency of results |
B |
A body of evidence including studies rated as 2++, directly applicable to the target population, and demonstrating overall consistency of results; or Extrapolated evidence from studies rated as 1++ or 1+ |
C |
A body of evidence including studies rated as 2+, directly applicable to the target population and demonstrating overall consistency of results; or Extrapolated evidence from studies rated as 2++ |
D |
Evidence level 3 or 4; or Extrapolated evidence from studies rated as 2+ |
SIGN provides also a way to mark the “Good practice points” which are important practical points that the guideline development group wish to emphasize but for which there is not, nor is there likely to be, any research evidence. These are not an alternative to evidence-based recommendations, and should only be used where there is no other means of highlighting the issue. A similar grading system has been adopted by the National Institute for Clinical Excellence (NICE), the independent organization responsible for providing United Kingdom national guidance on the promotion of good health and the prevention and treatment of diseases. On 1st April 2005 NICE joined the Health Development Agency to become the new National Institute for Health and Clinical Excellence. The grading system adopted is still based on the grading system proposed by the US Agency for Health Care Policy and Research. Which has been adapted from the Agency for Healthcare Policy and Research (AHCPR) system US Department of Health and Human Services, Public Health Service, Agency for Health Care Policy and Research (1992). Acute pain management: operative or medical procedures and trauma. Rockville MD: Agency for Health Care Policy and Research Publications.
GRADE OF EVIDENCE |
DESCRIPTION |
I a |
Evidence from a meta-analysis of randomized controlled trials |
I b |
Evidence from at least one randomized controlled trial |
II a |
Evidence from at least one controlled study without randomization |
II b |
Evidence from at least one other type of quasi-experimental study |
III |
Evidence from observational studies |
IV |
Evidence from expert committee reports or experts |
GRADE OF RECOMMENDATION |
DESCRIPTION |
A |
Directly based on category I evidence |
B |
Directly based on category II evidence or extrapolated from category I evidence |
C |
Directly based on category III evidence or extrapolated from category I or II evidence |
D |
Directly based on category IV evidence or extrapolated from category I, II or III evidence |
Another interesting CPGs grading is the “strength of recommendation”. The strength (or grade) of a recommendation for clinical practice is based on a body of evidence (typically more than one study). This approach takes into account the level of evidence of individual studies; the type of outcomes measured by these studies (patient-oriented or disease-oriented); the number, consistency, and coherence of the evidence as a whole; and the relationship between benefits, harms, and costs.
An example of strength of recommendations criteria is depicted in the following table. It is an adaptation coming from the Canadian guide to clinical preventive health care [4] and from US preventive services resources [5]:
Strength of Recommendation |
Description |
Criteria |
A |
Strongly recommended that clinicians routinely provide the intervention to eligible residents | Good quality of evidence and substantial net benefits |
B |
Recommended that clinicians routinely provide the intervention to eligible residents | Fair quality of evidence and substantial net benefit or Good quality of evidence and moderate net benefit or Fair quality of evidence and moderate net benefit |
C |
No recommendation for or against routine provision of the intervention | Good quality of evidence and small net benefit or Fair quality of evidence and small net benefit |
D |
Not recommended for routine provision of the intervention to asymptomatic residents | Good quality of evidence and zero/negative net benefit or Fair quality of evidence and zero/negative net benefit |
I |
Insufficient evidence for recommendation | Poor quality of evidence (conflicting results; balance between benefits and risks difficult to determine; and poor study design) |
Traditional Clinical Practice Guidelines Lifecycle »
[1]
Harbour R, Miller J.
A new system for grading recommendations in evidence based guidelines
BMJ 2001;323:334-6
[2]
Clinical Practice Guideline No.1: acute pain management: operative or medical procedures and trauma
Rockville (MD): US Department of Health and Human Services. Agency for Health Care Policy and Research; 1993. AHCPR Publication No. 92-0023
[3]
Scottish Intercollegiate Guidelines Network (SIGN). Methodology Review Group.
Report on the review of the method of grading guideline recommendations
Edinburgh; SIGN: 1999
[4]
The Canadian Guide to Clinical Preventive Health Care. Recommendations by Strength of Evidence.
Accessed March 12, 2003
[5]
US Preventive Services Task Force. Translating evidence into recommendations
Accessed March 6, 2003
