Addressing Competing Risks When Assessing the Impact of Health Services Interventions on Hospital Length of Stay.

Background: Although hospital length of stay is generally modeled continuously, it is increasingly recommended that length of stay should be considered a time-to-event outcome (i.e., time to discharge). Additionally, in-hospital mortality is a competing risk that makes it impossible for a patient to be discharged alive. We estimated the effect of trauma center accreditation on risk of being discharged alive while considering in-hospital mortality as a competing risk. We also compared these results with those from the "naive" approach, with length of stay modeled continuously.

Methods: Data include admissions to a level I trauma center in Quebec, Canada, between 2008 and 2017. We computed standardized risk of being discharged alive at specific days by combining inverse probability weighting and the Aalen-Johansen estimator of the cumulative incidence function. We estimated effect of accreditation using pre-post, interrupted time series (ITS) analyses, and the "naive" approach.

Results: Among 5,300 admissions, 12% died, and 83% were discharged alive within 60 days. Following accreditation, we observed increases in risk of discharge between the 7th day (4.5% [95% CI = 2.3, 6.6]) and 30th day since admission 3.8% (95% CI = 1.5, 6.2). We also observed a stable decrease in hospital mortality, -1.9% (95% CI = -3.6, -0.11) at the 14th day. Although pre-post and ITS produced similar results, we observed contradictory associations with the naive approach.

Conclusions: Treating length of stay as time to discharge allows for estimation of risk of being discharged alive at specific days after admission while accounting for competing risk of death.