Table 3.

Criteria list for determining the level of evidence for best evidence synthesis, adapted from Lievense et al (2001)[13]

Level of evidence	Criteria for inclusion in best evidence synthesis
Strong evidence	generally consistent findings in:
	o multiple high quality cohort studies
Moderate evidence	generally consistent findings in:
	o 1 high quality cohort study & > 2 high quality case-control studies
	o > 3 high quality case-control studies
Limited evidence	generally consistent findings in:
	o single cohort study
	o 1 or 2 case-control studies or
	o multiple cross-sectional studies
Conflicting evidence	inconsistent findings in <75% of the trials
No evidence	No studies could be found