| 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 |
[33] Prednisone: Burge P.S., Calverley P.M.A., Jones P.W., Spencer S., Anderson J.A., on behalf of the ISOLDE Study Group. 2003. Prednisolone response in patients with chronic obstructive pulmonary disease: results from the ISOLDE study. Thorax. Vol 58: 654-658 http://www.ncbi.nlm.nih.gov/pubmed/12885977