Reviewed and revised 26 August 2015
- different systems of categorising the quality of evidence, and individual studies, have been developed
- primarily used in evidence-based clinical guidelines
NHMRC LEVELS OF EVIDENCE
The following is the designation used by the Australian National Health and Medical Research Council (NHMRC):
- Level I
- Evidence obtained from a systematic review of all relevant randomised controlled trials.
- Level II
- Evidence obtained from at least one properly designed randomised controlled trial.
- Level III-1
- Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or some other method).
- Level III-2
- Evidence obtained from comparative studies with concurrent controls and allocation not randomised (cohort studies), case control studies, or interrupted time series with a control group.
- Level III-3
- Evidence obtained from comparative studies with historical control, two or more single-arm studies, or interrupted time series without a parallel control group.
- Level IV
- Evidence obtained from case series, either post-test or pre-test and post-test.
OXFORD CENTRE FOR EVIDENCE BASED MEDICINE 2011
- I – systemic review of all relevant RCTs OR an n=1 RCT
- II – Randomized trial or observational study with dramatic effect
- III – Non-randomized controlled cohort/follow-up study (observational)
- IV – Case-series, case-control studies, or historically controlled studies
- V – mechanism-based reasong (expert opinion, based on physiology, animal or laboratory studies)
- A – consistent level 1 studies
- B – consistent level 2 or 3 studies or extrapolations from level 1 studies
- C – level 4 studies or extrapolations from level 2 or 3 studies
- D – level 5 evidence or troubling inconsistent or inconclusive studies of any level
References and Links
FOAM and web resources
- Oxford Centre for Evidence-based Medicine – OCEMB Levels of Evidence System