There are three general types of epidemiologic experiments: community trials, field trials, and clinical trials. A clinical trial is a medical research study that tests new ways to prevent, screen, diagnose or treat a disease.Communitybased clinical trials can help more patients access clinical trials than ever before and make recruitment easier. Clinical trials power medical progress and allow principal investigators to test new ways to prevent, detect, and treat respiratory disease. Clinical trials are medical research studies that involve people. Trials can evaluate various interventions, which may be medical, surgical, or behavioural.