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Evidence Based Medicine (EBM)

This guide is designed to walk you through the Evidence Based Medicine process: the elements of a well-formulated clinical question, types of studies, and the key critical appraisal questions that help determine the validity of evidence.

Can valid results be applied to this particular patient?

Once you have appraised a systematic review or primary study you need to decide whether or not it's findings can be applied to your specific patient. In doing so, you should take into account your patient's unique characteristics, circumstances, and personal preferences.

Here are some questions you should ask in clinical decision making.

(From: Sackett DL, Straus SE, Richardson WS, Rosenberg W, Haynes RB. Evidence-based medicine: how to practice and teach EBM. 2nd ed. Sydney: Churchill Livingstone; 2000.)

Interventions (including SRs of intervention studies and studies of risk/harm)

  1. Is my patient different from those described in the study so that the results of the study are not applicable?
  2. Is the treatment feasible in my practice setting?
  3. What would be the potential benefits and harms (i.e. side-effects) for my patient from this treatment?
  4. What are my patient's values and expectations for both the outcome I am trying to prevent and the treatment on offer?

Further reading: How to use a noninferiority trial: users' guides to the medical literature. JAMA, 26 2012, Vol.308(24), pp.2605-11

Diagnostic tests

  1. Is the test available, affordable, accurate, and precise in this setting?
  2. Can I generate a clinically sensible estimate of my patient's pre-test probability?
  3. Will the resulting post-test probabilities affect my management and help my patient?


  1. Are the study patients similar to my patient?
  2. Will this evidence make a clinically important impact on my conclusions as to what to tell the patient?

Qualitative research

Clinical practice guidelines

The 'killer Bs' of Sackett et al.

  1. Is the 'burden' of illness (frequency in our community, or our patient's pre-test probability or expected event rate [PEER]) too low to warrant implementation?
  2. Are the 'beliefs' of individual patients or communities about the value of the interventions or their consequences incompatible with the guideline?
  3. Would the opportunity cost of implementing this guideline constitute a bad 'bargain' in the use of our energy or our community's resources?
  4. Are the 'barriers' (geographic, organisational, legal, or behavioural) so high that it is not worth trying to overcome them?