4. Types of Experimental Studies

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2. Community intervention trials


Community trials are an extension of field trials. In community trials the study group is the entire community, rather than individuals. Conceptually, the difference is whether or not the intervention is implemented separately for each individual. If only two communities are involved in a study, one of which will receive the intervention and the other will not, random assignment of the community that receives the intervention is not required; differences in baseline characteristics will be the same whatever the method of assignment-only the direction of the differences will be affected.

Example: to study the efficacy of adding fluoride to the community water supply to prevent dental decay, two similar towns in New York State were studied in the Newburgh-Kingston water fluoridation trial (Ast et al, 1956[1]). In one town, fluoride was added to the water supply; nothing was done to the other town. Residents of both towns had dental examinations over a period of several years to measure the effect of the intervention. The outcome was that fluoride helped to prevent parodontids.



[1] Am J Public Health Nations Health. 1956 Mar; 46(3): 265–271. doi: 10.2105/ajph.46.3.265