Table 3Domains used to assess strength of evidencea

Risk of biasDegree to which the included studies for a given outcome or comparison have a high likelihood of adequate protection against bias (i.e., good internal validity), assessed through two main elements:
  • Study design (e.g., RCTs or observational studies)
  • Aggregate quality of the studies under consideration.
Information for this determination comes from the rating of quality (good/fair/poor) done for individual studies
ConsistencyDegree to which reported effect sizes from included studies appear to have the same direction of effect. This can be assessed through two main elements:
  • Effect sizes have the same sign (that is, are on the same side of “no effect”)
  • The range of effect sizes is narrow
DirectnessRelates to whether the evidence links the interventions directly to health outcomes. For a comparison of two treatments, directness implies that head-to-head trials measure the most important health or ultimate outcomes. Evidence is indirect if:
  • It uses intermediate or surrogate outcomes instead of ultimate health outcomes. In this case, one body of evidence links the intervention to intermediate outcomes and another body of evidence links the intermediate to most important (health or ultimate) outcomes
  • It uses two or more bodies of evidence to compare interventions A and B, e.g., studies of A vs. placebo and B vs. placebo, or studies of A vs. C and B vs. C but not A vs. B.
Indirectness always implies that more than one body of evidence is required to link interventions to the most important health outcomes. Directness may be contingent on the outcomes of interest.
PrecisionPrecision is the degree of certainty surrounding an effect estimate with respect to a given outcome (i.e., for each outcome separately). If a meta-analysis was performed, this will be the confidence interval around the summary effect size.

Excerpted from Owens et al., 201069

From: Methods

Cover of Noncyclic Chronic Pelvic Pain Therapies for Women: Comparative Effectiveness
Noncyclic Chronic Pelvic Pain Therapies for Women: Comparative Effectiveness [Internet].
Comparative Effectiveness Reviews, No. 41.
Andrews J, Yunker A, Reynolds WS, et al.

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