Cinical trials are biomedical or health-related research studies in human beings that follow a pre-defined protocol. Two common types of studies are interventional and observational.
Research subjects are assigned by the investigator to a treatment or other intervention, and their outcomes are measured.
Individuals are observed and their outcomes are measured by the investigators. Data from large, prospective observational studies provide information about the safety and efficacy of medicines in daily clinical use. (from Diabetes Res Clin Pract. 2010 May;88 Suppl 1:S3-9)