Clinical Epidemiology and EBM Glossary: Clinical Study Design and M. .. http://www.vetmed.wsu.edu/courses-jmgay/GlossClinStudy.htm 1 of 1 12/1/2006 8:11 AM Clinical Study Types: (In order from strongest to weakest empirical evidence inherent to the design when properly executed.) A. Experimental Studies: The hallmark of the experimental study is that the allocation or assignment of individuals is under control of investigator and thus can be randomized. The key is that the investigator controls the assignment of the exposure or of the treatment but otherwise symmetry of potential unknown confounders is maintained through randomization. Properly executed experimental studies provide the strongest empirical evidence. The randomization also provides a better foundation for statistical procedures than do observational studies. 1. Randomized Controlled Clinical Trial (RCT): A prospective, analytical, experimental study using primary data generated in the clinical environment. Individuals similar at the beginning are randomly allocated to two or more treatment groups and the outcomes the groups are compared after sufficient follow-up time. Properly executed, the RCT is the strongest evidence of the clinical efficacy of preventive and therapeutic procedures in the clinical setting . a. Randomized Cross-Over Clinical Trial: A prospective, analytical, experimental study using primary data generated in the clinical environment. Individuals with a chronic condition are randomly allocated to one of two treatment groups, and, after a sufficient treatment period and often a washout period, are switched to the other treatment for the same period. This design is susceptible to bias if carry over effects from the first treatment occur. An important variant
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