Appraising the evidence

Almost all scientific studies are flawed and it would come as a surprise to some clinicians that some (perhaps most) published papers (ref 1) should be thrown in the bin rather than used to inform clinical practice.

The important thing is not to stop questioning. Curiosity has its own reason for existing.
Albert Einstein 1879-1955

Critical appraisal is a way of rapidly assessing published papers in order to sort out the relevant or valid papers from the poor quality or irrelevent ones.

Validity – is the degree to which the results of the study are likely to be true, believable and free from bias.

Bias – is any factor (other than the experimental factor) that could change the study results in a non-random way.

Critical appraisal is best carried out in a structured/standardised way using explicit criteria. Appraisal can help the clinician to assess:

  • Validity
  • Clinical importance
  • Clinical relevance


  1. Altman D. The scandal of poor medical research. (Editorial) BMJ 1994; 308: 283-284.


How to Read a Paper series (1997) by Trish Greenhalgh from The British Medical Journal

( In order to access these BMJ articles you will need to register with the BMJ )

Papers on appraisal from the Canadian Dental Journal series 2001

Study Design Series by Kate Ann Levin in the Evidence Based Dentistry Journal