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Individual studies in patient-oriented research, whether described as "comparative effectiveness" or using other terms, are based on underlying methodological designs. A simple taxonomy of study designs includes randomized controlled trials on the one hand, and observational studies (such as case series, cohort studies, and case-control studies) on the other. A rigid hierarchy of these designtypes is a fairly recentphenomenon, promotedas a tenet of "evidence-based medicine," with randomized controlled trials receiving gold-standard status in terms of producing valid results. Although randomized trials have many strengths, and contribute substantially to the evidence base in clinical care, making presumptionsaboutthe quality of a study basedsolelyoncategory of research design is unscientific. Both the limitations of randomized trials as well as the strengths of observational studies tend to be overlooked when a priori assumptions are made. This essay presents an argument in support of a more balanced approach to evaluating evidence, and discusses representative examples from the general medical as well as pulmonary and critical care literature. The simultaneous consideration of validity (whether results are correct "internally") and generalizability (how well results apply to "external" populations) is warranted in assessing whether a study's results are accurate for patients likely to receive the intervention- examining the intersection of clinical and methodological issues in what can be called a medicine-based evidence approach. Examination of cause-effect associations in patient-oriented research should recognize both the strengths and limitations of randomized trials as well as observational studies.
Keywords: epidemiologic research design; randomized controlled trials; cohort studies; case-control studies; evidence-based medicine
The spectrum of medical research includes studies in patientoriented (nonlaboratory) research that focus on an intact person or patient as the unit of observation. Patient-oriented research relies on the basic science of clinical epidemiology, and individual studies are often described using terms such as outcomes research or health services research. Comparative effectiveness research is a recent addition to this list, bolstered by $1.1 billion of funding from the American Recovery and Reinvestment Act of 2009. Several types of study design (research architecture) are commonly employed in patient-oriented research, including randomized controlled trials (RCTs) as well as observational studies, such as case reports, case series, cohort studies, and case- control studies. The RCT (a.k.a., randomized trial) achieved great popularity during the latter-half of the 20th century,...