Table 2

Modified US Preventive Services Task Force levels of certainty regarding net benefit

Level of certainty	Description
High	The available evidence usually includes consistent results from well-designed, well-conducted studies in representative care populations with joint pain. These studies assess the effects of the service on health outcomes. This conclusion is therefore unlikely to be strongly affected by the results of future studies. Examples: randomized controlled trials or large-scale observational studies with control groups.
Moderate	The available evidence is sufficient to determine the effects of the intervention on health outcomes, but confidence in the estimate is constrained by such factors as follows: The number, size, or quality of individual studies. Inconsistency of findings across individual studies. Limited generalizability of findings to individuals with joint pain. Different etiologies and phenotypes in the study subjects with joint pain. 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.
Low	The available evidence is insufficient to assess effects on health outcomes. Evidence is insufficient because of the following: 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 individuals with joint pain, or generalizable only to a small proportion of those with joint pain. 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 service is correct.’ The net benefit is defined as benefit minus harm of the 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 service.