Observational Epidemiology

In an observational epidemiologic study, an investigator observes what is occurring in a study population without intervening. Observational studies may be descriptive or analytic. Examples of analytic studies include case-control, cohort, cross-sectional, and ecologic studies, as well as hybrid designs. Measures of association often estimated from observational studies include relative risks, hazard ratios, odds ratios, standardized mortality (or incidence) ratios, and attributable fractions. Bias from inadequate measurement, suboptimal selection of study participants, and uncontrolled confounding is often of concern in observational studies. To assist in reaching conclusions, guidelines have been developed for evaluating the strength of evidence that an exposure is causally related to a disease.