Table 4.

Factors that may influence the quality level of a body of evidence.

Decrease QualityIncrease Quality
  1. Within study, risk of bias causes the overall analysis to be biased

  2. Indirectness of evidence (i.e., considering each of the following 4 PICO letters — participant, intervention, control, and outcome, especially surrogates). If any of the PICO factors are not directly clinically relevant, the evidence might be judged appropriate for downgrading

  3. Unexplained heterogeneity or inconsistency of results (including problems with subgroup analyses, making it difficult to interpret the overall metaanalysis)

  4. Lack of precision of the overall effect estimates (wide CI), when the overall analysis does not confirm that the effect size is evident

  5. Risk of publication bias

  1. A large magnitude of effect

  2. All plausible confounding would reduce a demonstrated effect or suggest a spurious effect when results show no effect

  3. Evidence of a dose-response gradient