Study design plays an important role in the quality, execution, and interpretation of biomedical and public health research ( 1– 12).

This manuscript is meant to provide an overview of study design types, strengths and weaknesses of common observational and interventional study designs. Additionally, each study design has potential limitations that are more severe and need to be addressed in the design phase of the study. Each study design has specific outcome measures that rely on the type and quality of data utilized. Interventional studies are often prospective and are specifically tailored to evaluate direct impacts of treatment or preventive measures on disease. These include diagnostic accuracy designs, diagnostic cohort designs, and diagnostic randomized controlled trials. An important subset of observational studies is diagnostic study designs, which evaluate the accuracy of diagnostic procedures and tests as compared to other diagnostic measures. Observational study designs include ecological designs, cross sectional, case-control, case-crossover, retrospective and prospective cohorts. Observational study designs, also called epidemiologic study designs, are often retrospective and are used to assess potential causation in exposure-outcome relationships and therefore influence preventive methods. Each design has its own strengths and weaknesses, and the need to understand these limitations is necessary to arrive at correct study conclusions. There are many study designs to choose from within two broad categories of observational and interventional studies. The appropriate choice in study design is essential for the successful execution of biomedical and public health research.

Definition retrospective study