Types of clinical studies. III. Cross-sectional studies

Cross-sectional studies are a common methodology to investigate etiological factors and interactions and hierarchization of interventions. They start with a defined population, sample or cohort of patients and simultaneously evaluate the results, their presumed predictive factors and subject characteristics; these studies are also known as prevalence studies, since they enable calculation of disease frequency in a particular sample. This type of study can be used to determine the discriminatory power of a diagnostic test, the predictive characteristics of a clinical finding, or the prevalence of a disease or etiology of an illness. The measure of association in cross-sectional studies is prevalence, the ratio between the diseased subjects at one point in time and all subjects at risk at that point in time. In this article we will present the methodological design and the advantages and disadvantages of cross-sectional studies.