| 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 |
[9] Paracetamol, oral (adults - chronic cancer pain): Wiffen PJ, Derry S, Moore RA, McNicol ED, Bell RF, Carr DB, McIntyre M, Wee B. Oral paracetamol (acetaminophen) for cancer pain. Cochrane Database Syst Rev.2017 Jul 12;7:CD012637. https://www.ncbi.nlm.nih.gov/pubmed/28700092