It Is Time to Reconsider Factorial Designs: How Bradford Hill and R. A. Fisher Shaped the Standard of Clinical...

Could medical research and quality improvement studies be more productive with greater use of multifactor study designs?

Drawing on new primary sources and the literature, we examine the roles of A. Bradford Hill and Ronald A. Fisher in introducing the design of experiments in medicine.

Hill did not create the randomized controlled trial, but he popularized the idea. His choice to set aside Fisher's advanced study designs shaped the development of clinical research and helped the single-treatment trial to become a methodological standard.

Multifactor designs are not widely used in medicine despite their potential to make improvement initiatives and health services research more efficient and effective. Quality managers, health system leaders, and directors of research institutes could increase productivity and gain important insights by promoting a broader use of factorial designs to study multiple interventions simultaneously and to learn from interactions.