Nonparametric estimation of the conditional tail index and extreme quantiles under random censoring

23International audienceIn this paper, we investigate the estimation of the tail index and extreme quantiles of a heavy-tailed distribution when some covariate information is available and the data are randomly right-censored. We construct several estimators by combining a moving-window technique (for tackling the covariate information) and the inverse probability-of-censoring weighting method, and we establish their asymptotic normality. A comprehensive simulation study is conducted to evaluate the finite-sample performance of the proposed estimators and to identify their application scope

Nonparametric estimation of the conditional extreme-value index with random covariates and censoring

International audienceEstimation of the extreme-value index of a heavy-tailed distribution is addressed when some random covariate information is available and the data are randomly right-censored. An inverse-probability-of-censoring-weighted kernel version of Hill's estimator of the extreme-value index is proposed and its asymptotic normality is established. Based on this, a Weissman-type estimator of conditional extreme quantiles is also constructed. A simulation study is conducted to assess the finite-sample behaviour of the proposed estimators

Mineralogical and physico-chemical characterizations of clay from Keur Saër (Senegal)

There is interest in exploiting and developing natural resources, particularly deposits of natural clays. Senegal has several clay mineral deposits for which chemical and mineralogical compositions have been little studied. Some of these natural materials are nowadays used in pottery and ceramics. To extend applications, a better basic knowledge is required and, for this objective, the raw clay and separated <2 μm clay fraction from Keur Saër (Senegal) were subjected to chemical and mineralogical studies. Several techniques including X-ray diffraction (XRD), thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, cation exchange capacity (CEC) measurements and solid state nuclear magnetic resonance (NMR) have been used to characterize the material. It was found that the raw clay and the separated clay fraction consist of a mineral mixture in which kaolinite is the main component. 29Si and 27Al MAS-NMR spectra show the presence of silicon atoms linked to three other silicon atoms via an oxygen atom and six coordinated Al atoms. Significant increases in the specific surface area and cation exchange capacity were observed on purification, reaching a maximum of about 73.2 m2g–1 and 9.5 meq/100 g for the separated fine clay fraction while the values for the raw material were around 28.9 m2g–1 and 7.3 meq/100 g

Effects of mutual health organizations on use of priority health-care services in urban and rural Mali: a case-control study

OBJECTIVE: To examine the effects of a community-based mutual health organization (MHO) on utilization of priority health services, financial protection of its members and inclusion of the poor and other target groups. METHODS: Four MHOs were established in two districts in Mali. A case-control study was carried out in which household survey data were collected from 817 MHO member households, 787 non-member households in MHO catchment areas, and 676 control households in areas without MHOs. We compiled MHO register data by household for a 22-month period. Outcome measures included utilization of priority services, health expenditures and out-of-pocket payments. Independent variables included individual, household and community demographic, socioeconomic and access characteristics, as determined through a household survey in 2004. FINDINGS: MHO members who were up to date on premium payments (controlling for education, distance to the nearest health facility and other factors) were 1.7 times more likely to get treated for fevers in modern facilities; three times more likely to take children with diarrhoea to a health facility and/or treat them with oral rehydration salts at home; twice as likely to make four or more prenatal visits; and twice as likely, if pregnant or younger than 5 years, to sleep under an insecticide-treated net (P < 0.10 or better in all cases). However, distance was also a significant negative predictor for the utilization of many services, particularly assisted deliveries. Household and individual enrolment in an MHO were not significantly associated with socioeconomic status (with the exception of the highest quintile), and MHOs seemed to provide some financial protection for their members. CONCLUSIONS: MHOs are one mechanism that countries strengthening the supply of primary care can use to increase financial access to - and equity in - priority health services