Asymptotic theory for the Cox model with missing time-dependent covariate

The relationship between a time-dependent covariate and survival times is usually evaluated via the Cox model. Time-dependent covariates are generally available as longitudinal data collected regularly during the course of the study. A frequent problem, however, is the occurence of missing covariate data. A recent approach to estimation in the Cox model in this case jointly models survival and the longitudinal covariate. However, theoretical justification of this approach is still lacking. In this paper we prove existence and consistency of the maximum likelihood estimators in a joint model. The asymptotic distribution of the estimators is given along with a consistent estimator of the asymptotic variance.Comment: Published at http://dx.doi.org/10.1214/009053606000000038 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Prevalence and burden of self-reported blindness and low vision for individuals living in institutions: a nationwide survey

BACKGROUND: The prevalence of self-reported low vision (LV) and blindness, and their associated disabilities, handicaps and socio-economic consequences for individuals living in institutions are poorly documented. METHODS: 2,075 institutions were selected at random and eight individuals were picked at random from the list of residents. Three groups of individuals were defined: blind, LV, and a control group (CG). These were compared after adjustment for age and co-morbidities. Of the 15,403 individuals, 14,603 interviews (94.9%) were completed. RESULTS: The prevalence of blindness was 1.6% and the LV 13.4%. Blind individuals needed assistance more often (OR: 2.65 to 11.35) than CG members while the assistance required by LV individuals was similar to that for the CG. Blind individuals required institution adaptation (building and furniture changes) more often than the CG. Blind (57.9%) and LV individuals (35.4%) were more often registered for social allowances. Monthly social allowances were EUR 86 higher for blind than LV individuals. Monthly family incomes were found to be similar between the three groups (from EUR 782 to 797). Social and demographic data, institution description, income, handicaps, disabilities, social allowances and details of daily activities were collected interviews CONCLUSION: The results demonstrate the impact of self-reported blindness and LV on daily life for patients living in institutions

Factors associated with psychological and behavioral functioning in people with type 2 diabetes living in France

<p>Abstract</p> <p>Background</p> <p>To identify demographic and clinical factors associated with psychological and behavioral functioning (PBF) in people with type 2 diabetes living in France.</p> <p>Methods</p> <p>In March 2002, approximately 10,000 adults, who had been reimbursed for at least one hypoglycemic treatment or insulin dose during the last quarter of 2001, received a questionnaire about their health status and PBF (3,646 responders). For this analysis, the 3,090 persons with type 2 diabetes, aged 18-85 years old were selected.</p> <p>PBF was measured with the adapted version of the Diabetes Health Profile for people with type 2 diabetes. This permitted the calculation of three functional scores - psychological distress (PD), barriers to activity (BA), and disinhibited eating (DE) - from 0 (worst) to 100 (best).</p> <p>Results</p> <p>Major negative associations were observed with PBF for microvascular complications (a difference of 6.7 in the BA score between persons with and without microvascular complications) and severe hypoglycemia (difference of 7.9 in the BA score), insulin treatment (-8.5 & -9.5 in the PD & BA scores respectively, as compared to treatment with oral hypoglycemic agents), non-adherence to treatment (-12.3 in the DE score for persons forgetting their weekly treatment), increasing weight (-8.5 & -9.7 in the PD & DE scores respectively, as compared to stable weight), at least one psychiatrist visit in 2001 (-8.9 in the DE score), and universal medical insurance coverage (-7.9 in the PD score) (due to low income).</p> <p>Conclusion</p> <p>Prevention and management of microvascular complications or adherence to treatment (modifiable factors) could be essential to preserving or improving PBF among people with type 2 diabetes. A specific approach to type 2 diabetes management may be required in groups with a low socioeconomic profile (particularly people with universal medical insurance coverage), or other non modifiable factors.</p

Modèle de Rasch et validation de questionnaires de qualité de vie

The assesment of quality of life has become an important problem in medicine. This assesment is aimed to evaluate the limitations induced by therapeutics on the daily life of patients. In most of cases, a questionnaire is administred to the patients in order to quantify their quality of life. Then, we have to construct a statistical model that links the items answers to an unobserved quantitative variable, here the quality of life. In most of the clinical studies, only linear linear modelizations are used. The purpose of this work is to study a new approach based on Rasch model[...][...] Nous présentons l'algorithme stochastique SEM et nous l'utilisons de façon originale dans le cadre du modèle de Rasch. Si cette utilisation apporte peu dans le cas classique, nous montrons qu'elle est quasiment incontournable dans le cas du modèle de Rasch pour données longitudinales. La fiabilité, ou précision d'une mesure obtenue par questionnaire, est presque toujours estimée par le coëfficient alpha de Cronbach. Nous avons proposé de généraliser le calcul de la fiabilité au cas du modèle de Rasch. Le coefficient alpha de Cronbach et le nouveau coefficient sont comparés à l'aide de simulations. Nous présentons les problèmes posés par l'évaluation de la qualité de vie et les méthodes actuellement utilisées pour la validation de questionnaires. Nous exposons ensuite les nouveaux test d'ajustement au modèle de Rasch et montrons comment ils apporter des réponses aux problèmes de la construction de mesures de qualité de vie. Dans la dernière partie de ce travail, nous avons proposé, en nous basant sur les estimations isotoniques des probabilités de réponse, un nouveau test de type Kolmogorov-Smirnov pour la comparaison de traits lents entre deux groupes.LORIENT-BU (561212106) / SudocSudocFranceF

Test de type log-rank pour l évolution de la qualité de vie liée à la santé

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Sur l'estimation non-paramétrique de la fonction d' "Egalisation Equipercentile" (applications à la qualité de vie)

PARIS-BIUSJ-Mathématiques rech (751052111) / SudocSudocFranceF