Critical appraisal is "the process of assessing and interpreting evidence by systematically considering its validity, results and relevance" (Bandolier, 2007, para. 1).
Critical appraisal uses intrinsic (research design etc) not extrinsic (author, journal, institution) factors which is more commonly used in evaluating web sites.
When appraising an article, it needs to meet the following three requirements:
Another aspect to consider when appraising evidence is: "How does this inform my practice?"
Bandolier. (2007). Critical appraisal.
Burls, A. (2009). What is critical appraisal?
These videos will provide an introduction to the concept of critical appraisal.
There are a number of checklists / tools available on the Internet to assist you in undertaking critical appraisal of evidence. Some examples are listed below.