Levels of Evidence

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Levels of Evidence

• Why?
• What?
• How?

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• Time-poor clinician suffering from Information
  Overload

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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 199631271-72).

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Steps in EBM
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The Evidence Pyramid is a guideline to the
hierarchy of study design
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Type of question type of study design
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NHMRC Levels of
Evidence
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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.

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• 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 lt15 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/pos
  t-randomisation exclusions
• 3. Blinding
• a. Blinding of outcome assessor

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NHMRC Grades of Recommendations
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Clinical Guidelines for Stroke Management 2010.
National Stroke Foundation
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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.
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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.
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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 ....

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• It is the well-defined research question that
  dictates the study design, not that every study
  should be a RCT because its 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.

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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

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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?pid167579
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