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RESEARCH PRODUCT

Study Design in Medical Research

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Medical research studies can be split into five phases—planning, performance, documentation, analysis, and publication (1, 2). Aside from financial, organizational, logistical and personnel questions, scientific study design is the most important aspect of study planning. The significance of study design for subsequent quality, the relability of the conclusions, and the ability to publish a study are often underestimated (1). Long before the volunteers are recruited, the study design has set the points for fulfilling the study objectives. In contrast to errors in the statistical evaluation, errors in design cannot be corrected after the study has been completed. This is why the study design must be laid down carefully before starting and specified in the study protocol. The term "study design" is not used consistently in the scientific literature. The term is often restricted to the use of a suitable type of study. However, the term can also mean the overall plan for all procedures involved in the study. If a study is properly planned, the factors which distort or bias the result of a test procedure can be minimized (3, 4). We will use the term in a comprehensive sense in the present article. This will deal with the following six aspects of study design: the question to be answered, the study population, the type of study, the unit of analysis, the measuring technique, and the calculation of sample size—, on the basis of selected articles from the international literature and our own expertise. This is intended to help the reader to classify and evaluate the results in publications. Those who plan to perform their own studies must occupy themselves intensively with the issue of study design.