Partitioning Time in Target Trial Emulation
This study addresses the vulnerability of standard estimators in target trial emulation to immortal time bias and time-varying confounding arising from inappropriate temporal discretization. By subdividing follow-up time windows, this work constructs directed acyclic graphs and ancestral multi-world networks to elucidate how intra-interval causal ordering influences estimation. Building on these insights, we derive the g-formula and rectify the clone-censor-weight estimator, proposing a refined approach that restores its validity under fine-grained time partitions. Ultimately, this research establishes an unbiased effect estimation methodology alongside principled criteria for selecting temporal discretization schemes. These contributions offer actionable guidance for clinical studies, enabling more accurate evaluations of treatment effects while mitigating biases inherent in conventional emulation frameworks.