Lesson 3: How to Construct Research Hypotheses, and Directed Acyclic Graphs

Abstract

It is no exaggeration to say that the appropriateness of “research hypotheses” governs the quality of clinical studies. However, few papers in the published literature describe how to set up research hypotheses and how to refine them, and many clinicians conduct clinical studies based on inadequate hypotheses. When setting up a research hypothesis, it is most important to properly define the subjects, exposure (intervention), controls, and results, and to repeatedly engage in discussions and debates based on counterfactual models. It is also important to establish a research plan and analysis plan based on direct acyclic graphs (DAGs), which in recent years have come to be used in the field of epidemiology, and to assess confounding factors that require adjustment. If several simple rules are thoroughly understood, DAGs are very useful tools, and they are useful both when conducting clinical studies and when reading papers.