Clinical & Community Trial Study Designs
Definition: A clinical or community trial is an intervention study in which the investigator assigns an exposure and watches for the outcome to develop. This is a type of analytical study design with the following characteristics:
- The investigator assembles groups of individuals for the specific purpose of systematically determining whether or not the risk of disease is different for individuals exposed or not exposed to a factor of interest
- An appropriate comparison group allows for hypothesis testing
- Resource intensive
- Good for calculating measures of association
Pharmaceutical companies often use clinical trials to test new drugs.
Example: At one time in the United States, poliomyelitis was one of the most feared of the childhood diseases. No one knew how to prevent paralytic polio, and there was no cure. The hot weather of late summer was "polio season," bringing on a rash of new cases of paralytic polio. In the United States from the 1920s to the 1950s, the warmer months of the year were known as "nightmare summers of quarantine and contagion."
Jane S. Smith described the speed at which polio epidemics became common occurrences. "At the start of the twentieth century, few people had ever heard of polio. It was not until the summer of 1916, when a devastating epidemic struck the New York area that polio entered into public consciousness. By the end of the summer, 27,000 people were paralyzed and 9,000 dead. For the next forty years, not a summer passed without an epidemic somewhere."
Dr. Jonas Salk developed a promising vaccine against poliomyelitis, and the National Foundation for Infantile Paralysis provided $7.5 million to run the 1954 Salk vaccine trials. Dr. Thomas Francis Jr., chairman of Epidemiology at the University Of Michigan School of Public Health, evaluated the results of the vaccine trials, which proved the vaccine to be safe and effective. The historic announcement took place at the University of Michigan on April 12, 1955.
Only by undertaking a massive study – with 1.8 million subjects, thousands of volunteers, and hundreds of locations in three different countries – could the vaccine be swiftly and robustly evaluated. If it worked, they’d know, and know for sure.
Francis, a pioneer of influenza vaccine development, insisted on what is known as a “double-blind” experiment for the field trial. Neither the physicians administering the shots, nor the children and their parents, would know whether it was the real Salk Vaccine in the syringe, or a fake. The rate at which each group succumbed to further polio infections would be closely tracked, and as a further measure, evaluated against a third group of children who had no shots at all.
