Longitudinal observational data on patients can be used to investigate causal effects of time‐varying treatments on time‐to‐event outcomes. Several methods have been developed for estimating such ...effects by controlling for the time‐dependent confounding that typically occurs. The most commonly used is marginal structural models (MSM) estimated using inverse probability of treatment weights (IPTW) (MSM‐IPTW). An alternative, the sequential trials approach, is increasingly popular, and involves creating a sequence of “trials” from new time origins and comparing treatment initiators and non‐initiators. Individuals are censored when they deviate from their treatment assignment at the start of each “trial” (initiator or noninitiator), which is accounted for using inverse probability of censoring weights. The analysis uses data combined across trials. We show that the sequential trials approach can estimate the parameters of a particular MSM. The causal estimand that we focus on is the marginal risk difference between the sustained treatment strategies of “always treat” vs “never treat.” We compare how the sequential trials approach and MSM‐IPTW estimate this estimand, and discuss their assumptions and how data are used differently. The performance of the two approaches is compared in a simulation study. The sequential trials approach, which tends to involve less extreme weights than MSM‐IPTW, results in greater efficiency for estimating the marginal risk difference at most follow‐up times, but this can, in certain scenarios, be reversed at later time points and relies on modelling assumptions. We apply the methods to longitudinal observational data from the UK Cystic Fibrosis Registry to estimate the effect of dornase alfa on survival.
The concept of frailty offers a convenient way to introduce unobserved heterogeneity and associations into models for survival data. In its simplest form, frailty is an unobserved random ...proportionality factor that modifies the hazard function of an individual or a group of related individuals. Frailty Models in Survival Analysis presents a compreh
Abstract
Introduction
Assessing objective measures of sleep fragmentation could yield important features reflecting impaired sleep quality in people with insomnia. Survival analysis allows the ...specific examination of the stability of NREM sleep, REM sleep and wake. The objective of this study was to assess the differences between survival dynamics of NREM sleep, REM sleep and wake between people with insomnia and healthy controls.
Methods
We analyzed polysomnography recordings from 88 people with insomnia and 92 healthy controls. For each participant, survival dynamics of REM sleep, NREM sleep and wake were represented using Weibull distributions. We used lasso penalized linear regression to analyze the difference between participant groups with respect to the Weibull scale and shape parameters, while correcting for age, sex, total sleep time and relevant interaction effects. Because comparisons were done for scale and shape parameters of REM sleep, NREM sleep and wake, a Bonferroni correction was applied, resulting in an alpha value of 0.05/6 = 0.0083.
Results
Significant effects of group were found for the NREM scale parameter (unstandardized model coefficient B=-0.79, t=-3.0, p=0.0035), and for the scale and shape parameters of wake (scale parameter B=7.6, t=2.8, p=0.0065; shape parameter B=0.20, t=2.9, p=0.0048). Results indicated that people with insomnia had less stable NREM sleep and more stable wake after sleep onset compared to healthy controls. Additionally, the altered distribution of wake segment lengths indicated an increased difficulty to fall asleep after longer awakenings in the insomnia group. However, these differences were mainly observed in younger participants. Significant effects of group for the survival parameters of REM sleep were not found.
Conclusion
As illustrated by our results, survival analysis can be very useful for disentangling different types of sleep fragmentation in people with insomnia. For instance, the current findings suggest that people with insomnia have an increased fragmentation of NREM sleep, but not necessarily of REM sleep. Additional research into the underlying mechanisms of NREM sleep fragmentation could possibly lead to a better understanding of impaired sleep quality in people with insomnia, and consequently to improved treatment.
Support (if any):
NPLs (Non-PerformingLoans), ou Créditos Não Performados são passivos resultantes de créditos inadimplentes. O mercado de compra e venda desse tipo de ativos vem crescendo em território nacional, ...alavancada pela expansão de crédito iniciada em meados de 2003. É de interesse de muitas empresascederem seus passivos em atraso para conseguir recuperar parte de seus recursos, além de eliminar o saldo devedor dos balanços, melhorando seus resultados. O passo inicial para a cessão de carteiras em atraso é estimar seu valor e projetar o montante com potencial de recuperação. Entretanto, existe uma hipótese pouca avaliada pelos investidores: a probabilidade do devedor estar vivo para quitar sua dívida. O objetivo deste artigoé verificar o impacto da probabilidade de sobrevivência do devedor na recuperação de crédito. Os resultados apontam que, ao considerar o fator atuarial de sobrevivência, a estimativa da recuperação tende a cair.
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