Overview of Clinical study design.

The goal of clinical study is to examine the associated factors to the disease and to assess the efficacy and safety of an investigational drug or procedure or device. Since the clinical study design is different according to the own characteristics of each type of the study, it is aimed to help researchers understand the design of each type of the clinical study, select the optimal type of study within the given research circumstances. Clinical studies are classified into the two main types, observational study and clinical trial, according to presence or absence of intervention applied to human for the study. Designs for case-control study, cohort study involving prospective study and retrospective study, case-control study within a cohort including nested case-control study, case cohort study, and cross-sectional study in observational study are explained. Also, controlled/non-controlled trial, randomized/non-randomized trial, open-label/blind trial, parallel/cross-over/factorial design trials and pragmatic trial are reviewed. Each type of clinical study has both advantages and disadvantages. Therefore, in consideration of the characteristics of designs of the study, the researcher must plan and proceed his or her study by choosing the type of the clinical study that can most scientifically achieve the study objective within the given study circumstances.