Mixture of normals probit models

This paper generalizes the normal probit model of dichotomous choice by introducing mixtures of normals distributions for the disturbance term. By mixing on both the mean and variance parameters and by increasing the number of distributions in the mixture these models effectively remove the normality assumption and are much closer to semiparametric models. When a Bayesian approach is taken, there is an exact finite-sample distribution theory for the choice probability conditional on the covariates. The paper uses artificial data to show how posterior odds ratios can discriminate between normal and nonnormal distributions in probit models. The method is also applied to female labor force participation decisions in a sample with 1,555 observations from the PSID. In this application, Bayes factors strongly favor mixture of normals probit models over the conventional probit model, and the most favored models have mixtures of four normal distributions for the disturbance term.Econometric models

Transcatheter closure of a large patent ductus arteriosus with the clamshell septal umbrella

AbstractIn 14 patients undergoing transcatheter closure of a large (>4 mm diameter) patent ductus arteriosus, occlusion was attempted with use of the Bard Clamshell septal umbrella. Patient age ranged from 0.7 to 30.4 years. Isolated patent ductus arteriosus was present in 11 patients; 3 had additional congenital heart lesions. Moderate or severe pulmonary hypertension was present in four patients. The diameter of the patent ductus arteriosus ranged from 4.5 to 14 mm, as determined by contrast injection through an 11F sheath or by balloon sizing; it appeared larger by this method than by the standard angiographic method.All 14 patent ductus arteriosi were successfully closed. Prior embolization of a Rashkind umbrella was the reason for using a Clamshell device in three patients; one additional embolization of a Clamshell device occurred. All errant devices were retrieved at cardiac catheterization, without associated hemodynamic instability. No other complications occurred. Among the 14 patients, 11 had complete ductal closure by Doppler color flow mapping at last follow-up and 3 had trivial residual Row. All four patients having associated complex lesions or pulmonary hypertension, or both, had symptomatic improvement after the procedure, although one child (with Shone's anomaly) died 3 months later.The Clamshell device provides stable and effective closure of a large patent ductus arteriosus, and allows transcatheter closure to be offered to some patients who were previously considered unsuitable for this procedure

Bayesian inference for dynamic choice models without the need for dynamic programming

Programming (Mathematics)

Management of coronary artery fistulae Patient selection and results of transcatheter closure

AbstractObjectivesWe report short-term findings in 33 patients after transcatheter closure (TCC) of coronary artery fistulae (CAF) and compare our results with those reported in the recent transcatheter and surgical literature.BackgroundTranscatheter closure of CAF has been advocated as a minimally invasive alternative to surgery.MethodsWe reviewed all patients presenting with significant CAF between January 1988 and August 2000. Those with additional complex cardiac disease requiring surgical management were excluded.ResultsOf 39 patients considered for TCC, occlusion devices were placed in 33 patients (85%) at 35 procedures and included coils in 28, umbrella devices in 6 and a Grifka vascular occlusion device in 1. Post-deployment angiograms demonstrated complete occlusion in 19, trace in 11, or small residual flow in 5. Follow-up echocardiograms (median, 2.8 years) in 27 patients showed no flow in 22 or small residual flow in 5. Of the 6 patients without follow-up imaging, immediate post-deployment angiograms showed complete occlusion in 5 or small residual flow in 1. Thus, complete occlusion was accomplished in 27 patients (82%). Early complications included transient ST-T wave changes in 5, transient arrhythmias in 4 and single instances of distal coronary artery spasm, fistula dissection and unretrieved coil embolization. There were no deaths or long-term morbidity. Device placement was not attempted in 6 patients (15%), because of multiple fistula drainage sites in 4, extreme vessel tortuosity in 1 and an intracardiac hemangioma in 1.ConclusionsA comparison of our results with those in the recent transcatheter and surgical literature shows similar early effectiveness, morbidity and mortality. From data available, TCC of CAF is an acceptable alternative to surgery in most patients

Statistical inference in the multinomial multiperiod probit model

Statistical inference in multinomial multiperiod probit models has been hindered in the past by the high dimensional numerical integrations necessary to form the likelihood functions, posterior distributions, or moment conditions in these models. We describe three alternative approaches to inference that circumvent the integration problem: Bayesian inference using Gibbs sampling and data augmentation to compute posterior moments, simulated maximum likelihood (SML) estimation using the GHK recursive probability simulator, and method of simulated moment (MSM) estimation using the GHK simulator. We perform a set of Monte-Carlo experiments to compare the performance of these approaches. Although all the methods perform reasonably well, some important differences emerge. The root mean square errors (RMSEs) of the SML parameter estimates around the data generating values exceed those of the MSM estimates by 21 percent on average, while the RMSEs of the MSM estimates exceed those of the posterior parameter means obtained via agreement via Gibbs sampling by 18 percent on average. While MSM produces a good agreement between empirical RMSEs and asymptotic standard errors, the RMSEs of the SML estimates exceed the asymptotic standard errors by 28 percent on average. Also, the SML estimates of serial correlation parameters exhibit significant downward bias.Econometric models