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Evidence-Based Practice

Appraise the evidence

Appraise the evidence
Appraising, or critiquing the evidence is an important stage of Evidence Based Practice. It is important to consider:

  • bias - study design, publication bias, author bias
  • currency of study
  • how similar the population of the study is to your patient
  • how big the study was
  • whether the study type is appropriate for the question being asked

Different evidence for different questions

Clinical questions will vary - you won't always be asking what the best treatment is. 

You will have questions about the best diagnostic tests, the prognosis of your patient or disease causation. 

Some study types are more robust than others.  The best evidence is the most robust study type, and eliminates bias as much as possible - well designed Randomised Controlled Trials(RCTs) minimise bias well. 

However, different study designs are best for different question types, partly due to ethics (you can't allocate harm to someone in an RCT), and partly due to practicalities.  There is a hierarchy of studies for evidence, but it differs, depending on the question type.

If there is no evidence available at the top level, step down to the next best available evidence type.
 

Question type Study type hierarchy
Intervention/Therapy Randomised Controlled Trial (RCT)
Diagnosis Cohort> Case-control> Cross-sectional
Risk, Prognosis Cohort> Case-control
Aetiology Cohort> Cross-sectional
Frequency Cross-sectional
Observational Qualitative

Based on table 2.4 in Hoffman, T, Bennett, S, Del Mar, C.  Evidence-based practice: across the health professions.  2nd ed. Sydney: Elsevier Churchill Livingstone; 2013, p 25.


There are two major Australian evidence hierarchies which take a question> appropriate study type approach.  The top level is always a Systematic Review of the best study type, eg. Systematic Review of RCTs for intervention questions.  See the National Health and Medical Research Council (NHMRC) evidence hierarchies, and the Joanna Briggs institute (JBI) hierarchies.


Critiquing tools

The appraisal, or evaluation step of Evidence Based Practice, ensures that you are basing your decision upon sound evidence that's relevant for your situation. 

There are studies of varying quality, and at times, the author or publisher may not maintain their objectivity. 

Why go as far as appraising the original study when there are Point of Care tools?
Even entries in Point of Care tools and Systematic Reviews which have collated evidence for particular questions need to be appraised.  The original studies will have more detail in them, and may be more recently published than Point of Care topic overviews or Systematic Reviews.

There are many online tools to assist with critiquing evidence.