Table 2

USPSTF levels of certainty regarding net benefit*

Level of certaintyDescription
HighThe available evidence usually includes consistent results from well-designed, well-conducted studies in representative 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. Examples—RCTs or large-scale observational studies with control groups.
ModerateThe available evidence is sufficient to determine the effects of the preventive service on health outcomes, but confidence in the estimate is constrained by such factors 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. Examples—a single large-scale observational study without control groups (multisite or single-site); multiple (>2) large retrospective studies (>20 subjects) or cohort studies.
LowThe 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.

  • Lack of information on important health outcomes.

More information may allow estimation of effects on health outcomes. Examples—case series or case reports or consensus-based recommendations from other sources.

  • *The USPSTF 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.

  • RCT, randomized controlled trial; USPSTF, US Preventive Services Task Force.