Table 1.

Criteria for ascertainment of evidence level for best-evidence synthesis, adapted from Lievense et al^{10 11}

Level of evidence	Criteria for inclusion in best-evidence synthesis
Strong evidence	Generally consistent findings in: Multiple high-quality cohort studies
Moderate evidence	Generally consistent findings in: One high-quality cohort study and >2 high quality case–control studies >3 high quality case–control studies
Limited evidence	Generally consistent findings in: Single cohort study One or two case–control studies or Multiple cross-sectional studies
Conflicting evidence	Inconsistent findings in <75% of the studies
No evidence	No studies could be found