Failure time studies with intermittent observation and losses to follow‐up.

In health research interest often lies in modeling a failure time process but in many cohort studies failure status is only determined at scheduled assessment times. While the assessment times may be fixed upon study entry, individuals may become lost to follow‐up and miss visits subsequent to the time of loss to follow‐up. We consider a three‐state model to characterize a joint failure and loss to follow‐up process, and use it to investigate the impact of dependent loss to follow‐up on standard parametric, nonparametric, and semiparametric analysis. The effect of dependent loss to follow‐up is mitigated by fitting the joint model. The performance of standard methods is studied using the asymptotic theory of misspecified models, and the finite sample performance is examined for the standard and joint analyses through simulation studies. An application to data from a youth smoking prevention study is presented for illustration. [ABSTRACT FROM AUTHOR]