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Levels of Evidence. Why? What? How?. Time-poor clinician suffering from Information Overload . Evidence-Based Medicine.

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levels of evidence
Levels of Evidence
  • Why?
  • What?
  • How?
evidence based medicine
Evidence-Based Medicine
  • EBM is ...”the conscientious, explicit and judicious use of current best evidence in making decisions about the care of an individual patient. It means integrating individual clinical expertise with the best available external clinical evidence from systematic research”

(Sackett, D. BMJ 1996;312:71-72).

nhmrc assessment of study quality grades of recommendations
NHMRC Assessment of study quality – Grades of Recommendations

1. The evidence base, in terms of the number of studies, level of evidence and quality of studies (risk of bias).

2. The consistency of the study results.

3. The potential clinical impact of the proposed recommendation.

4. The generalisability of the body of evidence to the target population for the guideline.

5. The applicability of the body of evidence to the Australian healthcare context.


Checklist for appraising the quality of studies of interventions (Cochrane handbook)

  • 1. Method of treatment assignment
  • a. Correct, blinded randomisation method described
  • OR randomised, double-blind method stated
  • AND group similarity documented
  • b. Blinding and randomisation stated but method not described
  • OR suspect technique (eg allocation by drawing from an envelope)
  • c. Randomisation claimed but not described and investigator not blinded
  • d. Randomisation not mentioned
  • 2. Control of selection bias after treatment assignment
  • a. Intention to treat analysis AND full follow-up
  • b. Intention to treat analysis AND <15% loss to follow-up
  • c. Analysis by treatment received only OR no mention of withdrawals
  • d. Analysis by treatment received
  • AND no mention of withdrawals
  • OR more than 15% withdrawals/loss-to-follow-up/post-randomisation exclusions
  • 3. Blinding
  • a. Blinding of outcome assessor
  • AND patient and care giver
  • b. Blinding of outcome assessor
  • OR patient and care giver
  • c. Blinding not done
  • 4. Outcome assessment (if blinding was not possible)
  • a. All patients had standardised assessment
  • b. No standardised assessment OR not mentioned
  • Source: National Health and Medical Research Council (NHMRC). How to review the evidence:
  • systematic identification and review of the scientific literature. Canberra: NHMRC, 1999: p.45

Brain Trauma, F., S. American Association of Neurological, et al. (2007). "Guidelines for the management of severe traumatic brain injury." Journal of Neurotrauma 24 Suppl 1.


Table 1. Applying Classification of Recommendations and Level of Evidence

Morgenstern, L. B., J. C. Hemphill, 3rd, et al. (2010). "Guidelines for the management of spontaneous intracerebral haemorrhage: a guideline for healthcare professionals from the American Heart Association/American Stroke Association." Stroke 41(9): 2108-29.

is evidence based surgery an oxymoron what if there is no level i evidence
Is Evidence-Based Surgery an oxymoron? What if there is no level I evidence?

Surgical RCTs have well-recognized disadvantages:

high costs, administrative complexity, prolonged time to completion, recruitment difficulty, blinding, randomization technique standardization, poor generalizability or external validity, patient compliance, underpowered studies, crossovers and drop outs, multiple surgical options, technological advancement, patient complexity, variability and preference and selection bias ....


It is the well-defined research question that dictates the study design, not that every study should be a RCT because it’s the gold standard”

  • “The proper use of evidence-based information is not the strict adherence to only RCTs, but more accurately, the informed and effective use of all types of evidence … Large, prospective cohort studies in a surgical setting are often thought to be on a par with RCTs and provide superior generalizability”

Fisher, C. G. and K. B. Wood (2007). "Introduction to and techniques of evidence-based medicine." Spine 32(19 Suppl): S66-72.

isat lancet 2002 lancet 2005
ISAT (Lancet, 2002; Lancet, 2005)
  • 9559 eligible patients, 2143 randomised
    • 43 Participating centres; enrolled 1-44% of eligible patients
  • Equipoise did not exist in over 75%
    • 3615 underwent surgery
    • 2737 underwent endovascular treatment
    • 1064 unknown treatment
  • Differences between groups
    • Cross-overs, time to treatment,
  • Small but significant difference in time between randomisation and first procedure
    • Coiling 1.1 days Surgery 1.7 days
  • Cross-overs
    • Coiling  surgery 9 patients
    • Surgery  coiling 38 patients
  • Different experience of INR and surgeons
  • Unknown differences between centres
using the evidence
Using the evidence....
  • Know which levels and grades of recommendations are being used and quote/reference them
  • Stay up to date with developments or changes to levels and grades
  • Use NHMRC levels and grades where possible
  • Look for other levels of evidence when RCTs or level 1 studies are not possible
  • Make evidence-based decisions
  • Become a lifelong learner of EBM http://libguides.mq.edu.au/content.php?pid=167579&sid=1412023