Weighted Cox Regression Using the R Package coxphw

Cox's regression model for the analysis of survival data relies on the proportional hazards assumption. However, this assumption is often violated in practice and as a consequence the average relative risk may be under- or overestimated. Weighted estimation of Cox regression is a parsimonious alternative which supplies well interpretable average effects also in case of non-proportional hazards. We provide the R package coxphw implementing weighted Cox regression. By means of two biomedical examples appropriate analyses in the presence of non-proportional hazards are exemplified and advantages of weighted Cox regression are discussed. Moreover, using package coxphw, time-dependent effects can be conveniently estimated by including interactions of covariates with arbitrary functions of time

Vascular morphometric changes after radioactivestent implantation: a dose-response analysis

AbstractObjectivesThe goal of this study was to evaluate the dose-dependency of morphometric changes in the coronary arterial wall after radioactive stenting.BackgroundRadioactive stents have been found to reduce intrastent intimal hyperplasia (IIH) but lead to a characteristic type of restenosis occurring predominantly at the stent edges.MethodsFifteen patients underwent intravascular ultrasound (IVUS) examination after implantation of a P-32 radioactive stent and at the six-month follow-up. The post-stent IVUS measurements on seven predefined locations of each lesion were subjected to a computer algorithm for the development of dose-volume histograms (DVH). Thus, we derived the radiation doses delivered to at least 10% and 90% of the adventitia (DV10, DV90). The IIH and vascular remodeling at follow-up were correlated with the doses in each segment.ResultsThe IIH was most pronounced at the stent edges and lowest in the stent-body, whereas we detected a significant expansive remodeling within the stent body. The delivered doses correlated with a decreased IIH (r = 0.52, p < 0.001 for DV10 and r = 0.62, p < 0.001 for DV90) and with expansive remodeling (r = 0.48, p = 0.009 for DV10 and r = 0.50, p = 0.006 for DV90). A DV10 >90 Gy or a DV90 >15 Gy reduced IIH and induced expansive remodeling. Plaque growth was not reduced by radioactive stents.ConclusionsThe DVH analysis reveals a dose-dependent increase of external elastic lamina area behind radioactive stents, whereas plaque growth is not reduced but inverted into an outward direction from the stent. A DV10 >90 Gy or a DV90 >15 Gy results in a beneficial long-term outcome after radioactive stenting

SPLUS and SAS

Fixing the nonconvergence bug in logistic regression wit