On Framing the Research Question and Choosing the Appropriate Research Design.

Clinical epidemiology is the science of human disease investigation with a focus on diagnosis, prognosis, and treatment. The generation of a reasonable question requires definition of patients, interventions, controls, and outcomes. The goal of research design is to minimize error, ensure adequate samples, measure input and output variables appropriately, consider external and internal validities, limit bias, and address clinical as well as statistical relevance. The hierarchy of evidence for clinical decision-making places randomized controlled trials (RCT) or systematic review of good-quality RCTs at the top of the evidence pyramid. Prognostic and etiologic questions are best addressed with longitudinal cohort studies.