Invited Commentary: The Prevalent New-User Design in Pharmacoepidemiology—Challenges and Opportunities

The prevalent new-user design includes a broader study population than the traditional new-user approach that is frequently used in pharmacoepidemiologic research. In an article appearing in this issue (Am J Epidemiol. 2021;190(7):1341-1348), Webster-Clark et al. describe the treatment initiator types included in the prevalent new-user design and contrast the causal questions assessed using a prevalent new-user design versus a new-user design. They further applied a series of simulation studies showing the importance of accounting for treatment history in addition to time since initiation of the comparator in the prevalent new-user design. In this commentary, we put their findings in the broader context with a discussion of the strengths and limitations of the prevalent new-user design and settings where it would be most useful. The prevalent new-user design and new-user design both address unique questions of clinical and public health importance. Real-world evidence generated by pharmacoepidemiologic research is increasingly being used by regulators and other knowledge users to inform their decision-making. Understanding the causal questions addressed by different designs is crucial in this process; the study by Webster-Clark et al. represents an important step in addressing this issue.