Idiopathic pulmonary fibrosis (IPF) is a rare condition for which reliable disease trends over time can be difficult to obtain. Understanding the epidemiology of IPF is crucial given its impact on quality of life and productivity of affected individuals and their families,1 as well as substantial costs to the healthcare system.2 The occurrence of IPF over time has likely changed with growing awareness of the disease, the advent of antifibrotic therapies that slow disease progression and multiple promising clinical trials that may alter the disease’s natural history. Knowledge of the incidence and prevalence of IPF informs healthcare needs, which range from access to specialists and pharmacotherapy to availability of hospice and resources for end-of-life care.

Although smaller studies based on primary sources (eg, medical chart review) exist,3 4 many epidemiological studies on IPF have used patient registries.5 Clinical registries allow for increased accuracy in case identification and more comprehensive data collection,6 which is particularly helpful in complex conditions like pulmonary fibrosis. Studying epidemiology using clinical registries is limited by the costs required to build and maintain them, evolving diagnostic criteria that may affect case identification,7 8 and referral bias given these databases are often located in …