What are the types of clinical trials?
A trial or study in which research subjects (patients) are assigned to receive a particular treatment (intervention) with response being documented by the researcher at specified intervals for a predetermined length of time, after which the results are compared to other subjects, usually patients who received a different intervention or no intervention at all. This type of trial may or may not be randomized. A randomized study is one in which subjects are assigned to one of two groups, the group receiving the intervention (usually a drug) and the group receiving a placebo (sugar pill) in random manner so that neither the subjects not the researchers knows to which group any given subject belongs.
Studies in which health outcomes are assessed in pre-defined groups of individuals. Subjects in this type study may receive diagnostic, therapeutic, or other interventions, but the investigator does not assign specific interventions to the subjects of the study and has no control over the behavior of the subjects. Such studies are often undertaken to determine risk factors for certain illnesses and behaviors in groups of individuals.