| 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 |
[4] Ipratropium: Rodrigo GJ, Castro-Rodriguez JA. Anticholinergics in the treatment of children and adults with acute asthma: a systematic review with meta-analysis. Thorax. 2005 Sep;60(9):740-6. Epub 2005 Jul 29. Review. Erratum in: Thorax. 2010 Dec;65(12):1118. Thorax. 2008 Nov;63(11):1029. Thorax. 2006 May;61(5):458.Thorax. 2006 Mar;61(3):274. http://www.ncbi.nlm.nih.gov/pubmed/16055613