Measuring patient persistency with drug therapy using methods for the design and analysis of natural history studies.

The same methodologic rigor should be applied in measuring both patient persistency with drug therapy and the natural history of disease: Investigators should design natural history cohort studies and evaluate the resulting data using survival analysis. Although simpler analyses, such as those based on the medication possession ratio, may allow identification of obvious drug therapy patterns, results of survival analyses allow more refined interpretations that may help decision makers improve disease management in the population-based setting. This paper explains how to design persistency studies as natural history studies whose outcomes can be analyzed using survival analysis.