Table 1

Strength of evidence assessment.

1Strong evidenceConsistent findings in multiple high-quality cohort and/or case–control studies.
2Moderate evidenceConsistent findings in multiple cohort and/or case–control studies, of which only one is a high-quality study
3Some evidenceFindings of one cohort or case–control study or consistent findings in multiple cross-sectional studies, of which at least one study is a high-quality study
4Inconclusive evidenceConcerns all other cases—that is, consistent findings in multiple low-quality, cross-sectional studies or inconsistent findings in multiple studies. The evidence is considered to be inconclusive if only one cross-sectional study is available, regardless of the quality of this study
  • Note: Findings are consistent when the results of at least 75% of the studies have similar outcomes.