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Communication Sciences & Disorders

Evidence Considerations

An understanding of how various levels of evidence are reported and how this literature is organized will help you retrieve the highest levels of evidence for a particular clinical question. High levels of evidence may not exist for all clinical questions because of the nature of medical problems and research and ethical limitations.
The following should be considered when evaluating  a piece of evidence:
  1. Does the study/evidence address my question?
  2. Is the source reliable?
  3. Is the research methodology sound?
  4. Are the results valid?
  5. Does the evidence apply to my patient or population?
If you answer NO to any of the question above, then it may be best to discard the evidence and find other research. 

Levels of Evidence

Hierarchy of Evidence

The hierarchy of evidence is a core principal of EBP. EBP hierarchies rank study types based on the strength and precision of their research methods. Different hierarchies exist for different question types, and even experts may disagree on the exact rank of information in the evidence hierarchies. 

Oxford Centre for Evidence-based Medicine – Levels of Evidence

Adapted from OCEBM Levels of Evidence Working Group*. “The Oxford Levels of Evidence 2”.
Oxford Centre for Evidence-Based Medicine.

* OCEBM Levels of Evidence Working Group = Jeremy Howick, Iain Chalmers (James Lind Library), Paul Glasziou, Trish Greenhalgh, Carl Heneghan, Alessandro Liberati, Ivan Moschetti, Bob Phillips, Hazel Thornton, Olive Goddard and Mary Hodgkinson


Hierarchy of Evidence Pyramid