[Research methods in clinical cardiology (I). Types of basic designs. Observational studies in clinical cardiology (I)].

Clinical investigation studies can be classified according to their purpose (causality, diagnosis, therapy, etc), by its research strategy (observation or intervention), by the characteristics of its design (descriptive or analytic) or according to the basic axes of the investigation process (directionality and time orientation); and the personal attributes (exposure and disease) of the study population. Among observational designs, the cross-sectional and ecological studies are the main representatives of descriptive research. Their main objectives are the estimation of disease prevalence and risk factor distribution in the population, as well as the comparison of prevalence and risk factor distribution among several populations. On the other hand, the aim of analytical studies is the identification of individual risk factors associated with the disease. The key difference between descriptive and analytical studies is the existence of a comparison group in the latter, which allow hypotheses testing. Examples or analytical studies are the case-control and cohort studies. This paper deal with the principles of basic design and methods of descriptive (cross-sectional and ecological), and case-control studies. Finally we outline the basic concepts and principles of the screening, a frequent objective in many cardiovascular surveys, specifically in primary prevention.