Chart 3. Factors that can affect the quality of evidence.^a .

Quality of evidence	Reasons for downgrading	Reasons for upgrading
• High • Moderate • Low • Very low	• Risk of bias • Indirect evidence • Inconsistency • Imprecision • Publication bias	• A strong association, with no plausible confounders • Evidence of dose response • All plausible confounders would have reduced the effect

^aAdapted from Guyatt et al. ³⁸