The time-dependent bias and its effect on extra length of stay due to XXXX .

@entity281 @entity580
OBJECTIVES: Many studies disregard the time dependence of @entity580 when examining length of hospital stay and the associated financial costs. This leads to the "time-dependent bias," which biases multiplicative hazard ratios. We demonstrate the time-dependent bias on the additive scale of extra length of stay. METHODS: To estimate the extra length of stay due to @entity281 , we used a multistate model that accounted for the time of @entity281 . For comparison we used a generalized linear model assuming a gamma distribution, a commonly used model that ignores the time of @entity281 . We applied these two methods to a large prospective cohort of hospital admissions from Argentina, and compared the methods' performance using a simulation study. RESULTS: For the Argentina data the extra length of stay due to @entity580 was 11.23 days when ignoring time dependence and only 1.35 days after accounting for the time of @entity281 . The simulations showed that ignoring time dependence consistently overestimated the extra length of stay. This overestimation was similar for different rates of @entity281 and even when an @entity281 prolonged or shortened stay. We show examples where the time-dependent bias remains unchanged for the true discharge hazard ratios, but the bias for the extra length of stay is doubled because length of stay depends on the @entity281 hazard. CONCLUSIONS: Ignoring the timing of @entity580 gives estimates that greatly overestimate its effect on the extra length of hospital stay.
