Levels and Grades of Evidence
Reviewed and revised 26 August 2015
OVERVIEW
- 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
Levels
- 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)
Grades
- 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
LITFL
FOAM and web resources
- Oxford Centre for Evidence-based Medicine – OCEMB Levels of Evidence System
- www.GradeWorkingGroup.org
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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