Critical appraisal enables you to assess a study's usefulness and if it is trustworthy. One can use the various checklists available to test a study by its type - Diagnosis, Harm, Prognosis, and Therapy, and/or by a research design from the Levels of Clinical Evidence Pyramid: case report, case control study, cohort studies, randomized controlled trials, systematic reviews. Be sure and use what is recommended by your instructor when completing assignments. Some sources are the Evidence Based Medicine website and CASP. There are three general questions you will want to consider: