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Considerations of Study DesignDepartment of Medicine, Olive View–UCLA Medical Center, Sylmar, California Correspondence: Ronald L. Koretz, MD, Department of Medicine, Olive View–UCLA Medical Center, 14445 Olive View Drive, Sylmar, CA 91342. Electronic mail may be sent to rkoretz{at}ladhs.org. Research projects attempt to answer specific questions. The particular study design that is selected will depend in large measure on the nature of the question and the time and resources available. There are 5 common categories of clinical questions; they relate to etiology, prognosis, utility of diagnostic tests, efficacy of proposed interventions, and cost of treatment in specific disease states. A number of study designs can be used. Case reports serve to memorialize unusual or novel aspects of diseases. Retrospective case series are useful for defining natural history. Case-control studies are used by epidemiologists to elucidate potential etiologies of diseases. Prospective cohort studies can be used to assess natural history or to assess potential disease etiologies. Controlled trials are designed to assess the efficacy of therapeutic interventions. Studies that define the sensitivity and specificity of diagnostic tests can be used to assess the utility of those tests. Economic analyses estimate the costs that particular diseases or therapies will require. Each of these study designs has limitations; with the exception of high-quality randomized trials, none of these study designs can establish a causative relationship between putative etiologic (or therapeutic) factors and disease (outcomes).
Nutrition in Clinical Practice, Vol. 22, No. 6,
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