The Clone-Censor-Weight Method in Pharmacoepidemiologic Research: Foundations and Methodological Implementation

Purpose of Review Over the past two decades, cautions have repeatedly been issued about the potential for immortal time bias in observational studies. This bias is particularly relevant in fields that routinely leverage large secondary databases such as pharmacoepidemiology. A variety of study design and analysis tools exist to prevent immortal time bias. A newer approach, the clone-censor-weight method, successfully eliminates the possibility for immortal time while maintaining a target trial emulation framework. We review the rationale for the clone-censor-weight approach, outline the steps for implementation, compare the method to other tools for handling immortal time, and describe how the method has been used in a convenience sample of applied studies. Recent Findings The clone-censor-weight method offers distinct advantages over other methods for handling immortal time bias, namely the retention of a target trial emulation framework. The clone-censor-weight method has been used across numerous substantive areas within pharmacoepidemiology, with variation in how the method is implemented. Summary The clone-censor-weight method represents a rigorous approach for emulating a target trial and preventing immortal time bias. Many pharmacoepidemiologic studies would benefit from appropriate use of this method, though future work should illuminate the impact of different implementation choices.