Critical appraisal methods assist the reader in assessing the validity (closeness to the truth) and the relevance (usefulness in everyday practice) of research findings. The specific techniques of critical appraisal can vary somewhat, depending on the nature of the research question. In this paper, the final in a 6-part series on evidence-based dentistry, frameworks are presented to enable the judicious reader of the dental literature to apply sensible questions to the evaluation of papers related to diagnosis, etiology and prognosis.