| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
[5] Zinc druation: Lazzerini M, Ronfani L. Summary of 'Oral zinc for treating diarrhoea in children', including tables of key finding and quality of included trials. Evid-Based Child Health. 2009; 4:1418-1422.