| 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 |
[13] Pain ladder (children): World Health Organisation. WHO guidelines on the pharmacological treatment of persisting pain in children with medical illnesses
http://whqlibdoc.who.int/publications/2012/9789241548120_Guidelines.pdf