Showing papers by "Hammou El Barmi published in 2002"
01 Jan 2002
TL;DR: In this article, the authors considered the competing risks problem with two risks and when the data are grouped or discrete and obtained nonparametric maximum likelihood estimates of the sub-survival functions corresponding to the two risks under the restriction that they are uniformly ordered and then used them to derive the likelihood ratio statistic for testing the null hypothesis of equality of the two sub-Survival functions against ordered alternatives.
Abstract: We consider the competing risks problem with two risks and when the data are grouped or discrete. We rstly obtain nonparametric maximum likelihood estimates of the sub-survival functions corresponding to the two risks under the restriction that they are uniformly ordered and then use them to derive the likelihood ratio statistic for testing the null hypothesis of equality of the two sub-survival functions against ordered alternatives. The asymptotic null distribution of the test statistic is seen to be of the chi-bar square ( 2 ) type. A simulation
11 citations
TL;DR: Simulation results suggest that the derived confidence intervals have acceptable coverage probabilities, even when sample sizes are small and the diagnostic tests have high accuracies.
Abstract: Nous envisageons une inference sur la vraisemblance de profil basee sur la distribution multinomiale pour evaluer la precision d'un test diagnostic. La methode s'applique a des donnees ordinales quand la precision est evaluee au moyen de l'aire sous la courbe caracteristique du receveur (courbe ROC). Des resultats de simulation suggerent que les intervalles de confiance derives ont vies probabilites de couverture acceptables, meme lorsque les tailles d'echantillons sont petites et que le test diagnostic a une haute precision. Les methodes s'etendent a des contextes stratifies, et a des situations ou les evaluations sont correlees. Nous illustrons les methodes sur des donnees provenant d'un essai clinique sur la detection du cancer de l'ovaire.
9 citations
TL;DR: In this paper, a binary search procedure was proposed to detect the changepoints in the sequence of the ratios of probabilities and obtain the maximum likelihood estimators of two multinomial probability vectors under the assumption that the probability ratio sequence has a changepoint.
Abstract: This article studies the problem of testing and locating changepoints in likelihood ratios of two multinomial probability vectors. We propose a binary search procedure to detect the changepoints in the sequence of the ratios of probabilities and obtain the maximum likelihood estimators of two multinomial probability vectors under the assumption that the probability ratio sequence has a changepoint. We also give a strongly consistent estimator for the changepoint location. An information theoretic approach is used to test the equality of two discrete probability distributions against the alternative that their ratios have a changepoint. Approximate critical values of the test statistics are provided by simulation for several choices of model parameters. Finally, we examine a real life data set pertaining to average daily insulin dose from the Boston Collaborative Drug Surveillance Program and locate the changepoints in the probability ratios.
5 citations
TL;DR: In this article, a non-parametric maximum likelihood estimator (NPMLE) f n of a nonincreasing probability density function f with distribution function F on the basis of a sample from a weighted distribution G with density given by g(x)=w(x)f(x)/μ(f,w), where w(u)>0 for all u and μ(m,m,w)=∫w(mf,mw),w),∫m(m),m)d u is the normalizing constant.
5 citations