a test or experiment, usually conducted under specific conditions.
clinical t. an internationally recognized research protocol designed to evaluate the efficacy or safety of drugs, vaccines, or other therapeutic agents, and to produce scientifically valid results.Four phases of trial are distinguished. Phase I trials usually involve fewer than 100 healthy volunteers who are exposed to a new drug or vaccine. Studies may attempt to gauge adverse reactions, optimal dose, and best route of administration. Phase II trials generally involve 200-500 volunteers randomly assigned to control and study groups. These are pilot efficacy studies, with emphasis on immunogenicity in the case of vaccines, and on relative efficacy and safety in the case of drugs. Phase III trials, often multicenter, involve thousands of volunteers, randomly assigned to control and study groups. The aim is to generate statistically relevant data. Phase IV trials are conducted after a national drug registration authority (in the U.S., the Food and Drug Administration) has approved an agent for distribution or sale. They may explore specific pharmacologic effect, adverse reactions, or long-term effects.
randomized controlled t. an epidemiological experiment in which subjects in a population are allocated randomly into groups, called "experimental" or "study" and "control" groups to receive or not receive an experimental therapeutic or preventive regimen, procedure, maneuver, or intervention.
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