| 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 |
[2] Surgical antibiotic prophylaxis: Centers for Disease Control and Prevention. Procedure-associated Module. Surgical Site Infection (SSI) Event. [Online] [Published April 2015; accessed December 2015] http://www.cdc.gov/nhsn/PDFs/pscManual/9pscSSIcurrent.pdf