18 research outputs found
Introduction to the Analysis of Survival Data in the Presence of Competing Risks
Competing risks occur frequently in the analysis of survival data. A competing risk is an event whose occurrence precludes the occurrence of the primary event of interest. In a study examining time to death attributable to cardiovascular causes, death attributable to noncardiovascular causes is a competing risk. When estimating the crude incidence of outcomes, analysts should use the cumulative incidence function, rather than the complement of the Kaplan-Meier survival function. The use of the Kaplan-Meier survival function results in estimates of incidence that are biased upward, regardless of whether the competing events are independent of one another. When fitting regression models in the presence of competing risks, researchers can choose from 2 different families of models: modeling the effect of covariates on the cause-specific hazard of the outcome or modeling the effect of covariates on the cumulative incidence function. The former allows one to estimate the effect of the covariates on the rate of occurrence of the outcome in those subjects who are currently event free. The latter allows one to estimate the effect of covariates on the absolute risk of the outcome over time. The former family of models may be better suited for addressing etiologic questions, whereas the latter model may be better suited for estimating a patientâs clinical prognosis. We illustrate the application of these methods by examining cause-specific mortality in patients hospitalized with heart failure. Statistical software code in both R and SAS is provided
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Can the optimal cervical length for placing ultrasoundâindicated cerclage be identified?
ObjectiveTo assess a continuum of cervical length (CL) cut-offs for the efficacy of ultrasound-indicated cerclage in women with previous spontaneous preterm birth (PTB).MethodsThis was a planned secondary analysis of a multicenter randomized clinical trial of ultrasound-indicated cerclage for the prevention of PTB in high-risk women. The efficacy of cerclage for preventing recurrent PTB <â35, <â32 andâ<â24âweeks' gestation was assessed using multivariable logistic regression analysis. Odds ratios (ORs) and CIs were estimated for a range of CL cut-offs using bootstrap regression. The 2.5(th) and 97.5(th) percentiles of bootstrapped ORs determined the CIs. Results were illustrated using smoothed curves superimposed on estimated ORs by CL cut-off.ResultsOf 301 women with a CL <â25âmm, 142 underwent ultrasound-indicated cerclage and 159 did not have cerclage placement. The few cases with CL <â10âmm limited the evaluation to CL cut-offs betweenâ<â10âmm andâ<â25âmm. For PTB <â35âweeks, ORs in women with a cerclage and CL <â25âmm were statistically significantly lower than in those without cerclage, and efficacy was maintained at smaller CL cut-offs. Results were similar for PTB <â32âweeks. For PTB <â24âweeks, results differed, with ORs increasing toward unity (no benefit), with wide CIs, for CL cut-offs betweenâ<â10âmm andâ<â15âmm, attributed to the small number of birthsâ<â24âweeks.ConclusionsThe efficacy of ultrasound-indicated cerclage in women with previous spontaneous PTB varies by action point CL cut-off and by PTB gestational age of interest. Cerclage significantly reduces the risk of PTB <â35 andâ<â32âweeks, at CL cut-offs betweenâ<â10âmm andâ<â25âmm, with the greatest reduction at shorter CL, affirming that women with prior spontaneous PTB and a short CL are appropriate candidates for ultrasound-indicated cerclage. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd