Agency for Healthcare Research and Quality (AHRQ)

Disclosures

March 01, 2012

In This Article

Strength of Evidence and Recommendation Grading System

ACCF/AHA (2010)

Applying Classification of Recommendations and Level of Evidence

Size of Treatment Effect

  • CLASS I
    Benefit >>> Risk
    Procedure/treatment SHOULD be performed/administered

  • CLASS II a
    Benefit >> Risk Additional studies with focused objectives needed
    IT IS REASONABLE to perform procedure/administer treatment

  • CLASS II b
    Benefit ≥ Risk
    Additional studies with broad objectives needed; additional registry data would be helpful Procedure/treatment MAY BE CONSIDERED

  • CLASS III No Benefit
    Procedure/test: Not helpful
    Treatment: No proven benefit

  • CLASS III Harm
    Procedure/test: Excess cost without benefit or harmful
    Treatment: Harmful to patients

Estimate of Certainty (Precision) of Treatment Effect

LEVEL A

Multiple populations evaluated*

Data derived from multiple randomized clinical trials or meta-analyses

Class I

  • Recommendation that procedure or treatment is useful/effective

  • Sufficient evidence from multiple randomized trials or meta-analyses

Class II a

  • Recommendation in favor of treatment or procedure being useful/effective

  • Some conflicting evidence from multiple randomized trials or meta-analyses

Class II b

  • Recommendation's usefulness/efficacy less well established

  • Greater conflicting evidence from multiple randomized trials or meta-analyses

Class III

  • Recommendation that procedure or treatment is not useful/effective and may be harmful

  • Sufficient evidence from multiple randomized trials or meta-analyses

LEVEL B

Limited populations evaluated*

Data derived from a single randomized clinical trials or nonrandomized studies

Class I

  • Recommendation that procedure or treatment is useful/effective

  • Evidence from single randomized trial or nonrandomized studies

Class II a

  • Recommendation in favor of treatment or procedure being useful/effective

  • Some conflicting evidence from single randomized trial or nonrandomized studies

Class II b

  • Recommendation's usefulness/efficacy less well established

  • Greater conflicting evidence from single randomized trial or nonrandomized studies

Class III

  • Recommendation that procedure or treatment is not useful/effective and may be harmful

  • Evidence from single randomized trial or nonrandomized studies

LEVEL C

Very limited populations evaluated*

Only consensus opinion of experts, case studies or standard of care

Class I

  • Recommendation that procedure or treatment is useful/effective

  • Only expert opinion, case studies, or standard-of-care

Class II a

  • Recommendation in favor of treatment or procedure being useful/effective

  • Only diverging expert opinion, case studies, or standard-of-care

Class II b

  • Recommendation's usefulness/efficacy less well established

  • Only diverging expert opinion, case studies, or standard-of-care

Class III

  • Recommendation that procedure or treatment is not useful/effective and may be harmful

  • Only expert opinion, case studies, or standard-of-care

*Data available from clinical trials or registries about the usefulness/efficacy in different subpopulations, such as gender, age, history of diabetes, history of prior myocardial infarction, history of heart failure, and prior aspirin use. A recommendation with Level of Evidence B or C does not imply that the recommendation is weak. Many important clinical questions addressed in the guidelines do not lend themselves to clinical trials. Even though randomized trials are not available, there may be a very clear clinical consensus that a particular test or therapy is useful or effective.

NACB (2009)

Weight of Evidence

  1. Data derived from multiple randomized clinical trials that involved large numbers of patients

  2. Data derived from a limited number of randomized trials that involved small numbers of patients or from careful analyses of nonrandomized studies or observational registries

  3. Expert consensus was the primary basis for the recommendation

Modified American College of Cardiology/American Heart Association Classifications: Summary of Indications

  1. Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective

  2. Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment

    1. Weight of evidence/opinion is in favor of usefulness/efficacy

    2. Usefulness/efficacy is less well established by evidence/opinion

  3. Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful/effective and in some cases may be harmful

USPSTF (2009)

What the USPSTF Grades Mean and Suggestions for Practice

GRADE A

Grade Definition: The USPSTF recommends the service. There is high certainty that the net benefit is substantial.

Suggestions for Practice: Offer or provide this service.

GRADE B

Grade Definition: The USPSTF recommends the service. There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial.

Suggestions for Practice: Offer or provide this service.

GRADE C

Grade Definition: The USPSTF recommends against routinely providing the service. There may be considerations that support providing the service in an individual patient. There is moderate or high certainty that the net benefit is small.

Suggestions for Practice: Offer or provide this service only if other considerations support offering or providing the service in an individual patient.

GRADE D

Grade Definition: The USPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.

Suggestions for Practice: Discourage the use of this service.

I STATEMENT

Grade Definition: The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined.

Suggestions for Practice: Read "Clinical Considerations" section of USPSTF Recommendation Statement (see "Major Recommendations" field). If this service is offered, patients should understand the uncertainty about the balance of benefits and harms.

USPSTF Levels of Certainty Regarding Net Benefit

Definition: The U.S. Preventive Services Task Force defines certainty as "likelihood that the USPSTF assessment of the net benefit of a preventive service is correct." The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service.

Level of Certainty: High

Description: The available evidence usually includes consistent results from well-designed, well-conducted studies in representative primary care populations. These studies assess the effects of the preventive service on health outcomes. This conclusion is therefore unlikely to be strongly affected by the results of future studies.

Level of Certainty: Moderate

Description: The available evidence is sufficient to determine the effects of the preventive service on health outcomes, but confidence in the estimate is constrained by factors such as:

  • The number, size, or quality of individual studies

  • Inconsistency of findings across individual studies

  • Limited generalizability of findings to routine primary care practice

  • Lack of coherence in the chain of evidence

As more information becomes available, the magnitude or direction of the observed effect could change, and this change may be large enough to alter the conclusion.

Level of Certainty: Low

Description: The available evidence is insufficient to assess effects on health outcomes. Evidence is insufficient because of:

  • The limited number or size of studies

  • Important flaws in study design or methods

  • Inconsistency of findings across individual studies

  • Gaps in the chain of evidence

  • Findings not generalizable to routine primary care practice

  • A lack of information on important health outcomes.

More information may allow an estimation of effects on health outcomes.

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