[Clinical research I. The importance of the research design].

The endeavor of clinical research to study a group of patients is to make a diagnosis, estimate the prognosis and prove a treatment. For this purpose is used the scientific method: 1) the architectural arrangement, which can be divided into cause-effect and the process of research; 2) the methodological approach, which includes controlled clinical trials, cohorts, case control, and cross-sectional designs; 3) the goal-oriented approach, in which studies on diagnostic tests, prognosis, treatment and risk or causal factors are grouped. The designs mentioned above are considered primary studies; it means that the information was obtained directly from the subjects studied. There is a second category of studies, which uses information obtained from the primary studies. This is the reason why they are considered as secondary or integrative studies.