| 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 |
[30] Long-acting β2-agonist/corticosteroid combination inhaler:Nannini LJ, Poole P, Milan SJ, Kesterton A. Combined corticosteroid and long-acting beta(2)-agonist in one inhaler versus inhaled corticosteroids alone for chronic obstructive pulmonary disease. Cochrane Database Syst Rev. 2013 Aug 30;8:CD006826. http://www.ncbi.nlm.nih.gov/pubmed/23990350
Long-acting β2-agonist/corticosteroid combination inhaler:Kew KM, Dias S, Cates CJ. Long-acting inhaled therapy (beta-agonists,anticholinergics and steroids) for COPD: a network meta-analysis. CochraneDatabase Syst Rev. 2014 Mar 26;3:CD010844. http://www.ncbi.nlm.nih.gov/pubmed/24671923