Table 3.

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 populations with suspected cervicogenic headache and/or facetogenic pain and/or compelling evidence from non-randomized studies. The studies assess the effects of the treatment, test, or other intervention on treatment or other relevant outcomes. The conclusion is therefore unlikely to be strongly affected by the results of future studies
Moderate	The available evidence is sufficient to determine the effects of the intervention on 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 individuals with suspected cervicogenic headache and/or cervical facetogenic pain High likelihood of bias Lack of coherence in the chain of evidence As more information becomes available, the magnitude or direction of the observed effect could change, and that change may be large enough to alter the conclusion
Low	The available evidence is insufficient to assess effects on treatment and other outcomes of interest. 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 High likelihood of bias Findings not generalizable to individuals with suspected cervicogenic headache and/or cervical facetogenic pain Lack of information on important outcome measures More information may allow estimation of effects on treatment outcomes

Note, the levels of certainty described in the definitions for the grading of evidence in table 2 refer solely to the magnitude of benefit attributed to the intervention, while the levels of certainty in table 3 consider the basis of evidence for the recommendation and the likelihood the recommendation will be affected by future studies. Whereas the two are related, the grading of evidence and rating of certainty were considered separately.