13 research outputs found
Frailty modeling of multivariate times to events based on positive stable family
Random effect models are extremely useful for multivariate times to events analysis (Hougaard, 2000); examples abound in the survival analysis literature. Dependent multivariate times to events are available in many cases where subjects in the same group are related to each other or when there are multiple recurrence times of events for the same subject. The variability in times to events data arises due to the variation within subjects and between subjects. The variation among subjects within the same groups may be explained by a random effect known as frailty in the survival analysis literature. The positive stable distribution is an attractive candidate as a frailty distribution because it has certain unique features, and also allows for more heterogeneity, permitting flexible modeling. I pursue different functions of positive stable frailty models, which enable us to capture more heterogeneity and describe the rich dependence structure. Lack of a closed form expression for the density function of the positive stable distribution makes likelihood based inference cumbersome for the PVF frailty model (the PVF is a transformed form of the positive stable), the additive positive stable frailty model, and the bivariate positive stable frailty model, which is discussed here. Incorporating an auxiliary variable, I describe fully Bayesian inference for such models, which permits simultaneous inference of all the model parameters. I also describe the dependence measures for the shared PVF frailty, and the multivariate positive stable frailty models.
Bivariate positive stable frailty models
This article describes inference for dependent multivariate times-to-events using a bivariate positive stable frailty model with a Weibull baseline hazard. Suitable Markov chain Monte Carlo algorithms facilitate Bayesian inference. The method is illustrated using a study conducted by the Air Force Research Laboratory on times to symptoms of decompression sickness in human subjects.
Recommended from our members
1151 Linaclotide Safety and Efficacy in Children Aged 6 to 17 Years With Functional Constipation
Recommended from our members
911 LINACLOTIDE SAFETY AND EFFICACY IN CHILDREN AGED 7 TO 17 YEARS WITH IRRITABLE BOWEL SYNDROME WITH CONSTIPATION
Sa1127 – Intestinal Guanylate Cyclase C Mrna Expression is Similar Across Children Aged 6 Months to ≪18 Years and is Greater in the Duodenum As Compared to the Colon
Recommended from our members
Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies.
Three phase 2 trials were conducted to assess the efficacy and long-term safety of weight-based memantine extended release (ER) treatment in children with autism spectrum disorder. MEM-MD-91, a 50-week open-label trial, identified memantine extended-release treatment responders for enrollment into MEM-MD-68, a 12-week randomized, double-blind, placebo-controlled withdrawal trial. MEM-MD-69 was an open-label extension trial in which participants from MEM-MD-68, MEM-MD-91, and open-label trial MEM-MD-67 were treated ⩽48 weeks with memantine extended release. In MEM-MD-91, 517 (59.6%) participants were confirmed Social Responsiveness Scale responders at week 12; mean Social Responsiveness Scale total raw scores improved two to three times a minimal clinically important difference of 10 points. In MEM-MD-68, there was no difference between memantine and placebo on the primary efficacy parameter, the proportion of patients with a loss of therapeutic response (defined as ⩾10-point increase from baseline in Social Responsiveness Scale total raw score). MEM-MD-69 exploratory analyses revealed mean standard deviation improvement in Social Responsiveness Scale total raw score of 32.4 (26.4) from baseline of the first lead-in study. No new safety concerns were evident. While the a priori-defined efficacy results of the double-blind trial were not achieved, the considerable improvements in mean Social Responsiveness Scale scores from baseline in the open-label trials were presumed to be clinically important
Recommended from our members
Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies.
Three phase 2 trials were conducted to assess the efficacy and long-term safety of weight-based memantine extended release (ER) treatment in children with autism spectrum disorder. MEM-MD-91, a 50-week open-label trial, identified memantine extended-release treatment responders for enrollment into MEM-MD-68, a 12-week randomized, double-blind, placebo-controlled withdrawal trial. MEM-MD-69 was an open-label extension trial in which participants from MEM-MD-68, MEM-MD-91, and open-label trial MEM-MD-67 were treated ⩽48 weeks with memantine extended release. In MEM-MD-91, 517 (59.6%) participants were confirmed Social Responsiveness Scale responders at week 12; mean Social Responsiveness Scale total raw scores improved two to three times a minimal clinically important difference of 10 points. In MEM-MD-68, there was no difference between memantine and placebo on the primary efficacy parameter, the proportion of patients with a loss of therapeutic response (defined as ⩾10-point increase from baseline in Social Responsiveness Scale total raw score). MEM-MD-69 exploratory analyses revealed mean standard deviation improvement in Social Responsiveness Scale total raw score of 32.4 (26.4) from baseline of the first lead-in study. No new safety concerns were evident. While the a priori-defined efficacy results of the double-blind trial were not achieved, the considerable improvements in mean Social Responsiveness Scale scores from baseline in the open-label trials were presumed to be clinically important