| 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 |
[6] Proton pump inhibitor, oral (duration of 4 weeks): McDonagh MS, Carson S, Thakurta S. Drug Class Review:
Proton Pump Inhibitors: Final Report Update 5 [Internet]. Portland (OR): Oregon Health & Science University; 2009 May. Available from http://www.ncbi.nlm.nih.gov/books/NBK47260/