| 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 |
[1] Antivirals to treat varicella zoster, oral- adults (therapeutic class):Tunbridge AJ, Breuer J, Jeffery KJ; British Infection Society. Chickenpox in adults - clinical management. J Infect. 2008 Aug;57(2):95-102. https://www.ncbi.nlm.nih.gov/pubmed/18555533