Levels and Grades of Evidence

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


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.



  • 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

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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