The aim of the present study was to calculate reference equations for carbon monoxide and nitric oxide transfer, measured in two distinct populations.The transfer factor of the lung for nitric oxide (TL,NO) and carbon monoxide (TL,CO) were measured in 303 people aged 18-94 yrs. Measurements were similarly made in two distant cities, using the single-breath technique. Capillary lung volume (Vc) and membrane conductance, the diffusing capacity of the membrane (Dm), for carbon monoxide (Dm,CO) were derived.The transfer of both gases appeared to depend upon age, height, sex and localisation. The rate of decrease in both transfers increased after the age of 59 yrs. TL,NO/alveolar volume (VA) and TL,CO/VA were only age-dependent. The mean TL,NO/TL,CO was 4.75 and the mean Dm/Vc was 6.17 min ; these parameters were independent of any covariate. Vc and Dm,CO calculations depend upon the choice of coefficients included in the Roughton-Forster equation. Values of 1.97 for Dm,NO/Dm,CO ratio and 12.86 min?kPa -1 for 1/red cell CO conductance are recommended.The scatter of transfer reference values in the literature, including the current study, is wide. The present results suggest that differences might be due to the populations themselves and not the methods alone.KEYWORDS: Ageing, capillary lung volume, carbon monoxide, diffusion, nitric oxide, pollution T he measurement of the transfer of gases through the lung is one of the few tests aimed at investigating alveolar function. The 1957 model and equation of ROUGHTON and FORSTER [1] permitted the transfer of carbon monoxide through the aveolocapillary structure to be split into two resistances, one for the alveolar membrane (1/membrane conductance, the diffusing capacity of the membrane (Dm), for carbon monoxide (Dm,CO)) and the other for the blood reacting with the gas (1/HCOVc), where HCO is the red cell conductance at a concentration, set by the pioneers of the method, of 14.9 g?dL -1 [2] and Vc the capillary lung volume:where TL,CO is the transfer factor of the lung for carbon monoxide. The first technique used to solve this equation with two unknowns, Dm and Vc, was to measure two transfers of CO, one under conditions of normoxia the other under hyperoxia. Breathing O 2 , by reducing HCO, lowers the TL,CO. GUENARD et al.[3] first published measurements of Dm and Vc using transfer factor of the lung for nitric oxide (TL,NO) and TL,CO and assuming HNO to be infinity, i.e. TL,NO5Dm,NO.The transfer of CO is dependant upon both Dm and Vc with HCO as a finite value.The relationship between Dm for nitric oxide (Dm,NO) and Dm,CO introduces a constant a: Dm,NO5aDm,CO. Therefore, the measurement of NO transfer alone permits the calculation of Dm,CO and, by introducing the latter into the CO transfer equation, of Vc.Most published reference values for Dm and Vc have been derived from the first two-step technique; one used the NO/CO method in a population of 127 healthy adults with a mean¡SD age of ,40¡12 yrs [4] and another focused on NO transfer in a population of 1...

We consider models based on multivariate counting processes, including multi-state models. These models are specified semi-parametrically by a set of functions and real parameters. We consider inference for these models based on coarsened observations, focusing on families of smooth estimators such as produced by penalized likelihood. An important issue is the choice of model structure, for instance, the choice between a Markov and some non-Markov models. We define in a general context the expected Kullback-Leibler criterion and we show that the likelihood-based cross-validation (LCV) is a nearly unbiased estimator of it. We give a general form of an approximate of the leave-one-out LCV. The approach is studied by simulations, and it is illustrated by estimating a Markov and two semi-Markov illness-death models with application on dementia using data of a large cohort study. Copyright 2007 Board of the Foundation of the Scandinavian Journal of Statistics..

We develop a general dynamical model as a framework for causal interpretation. We first state a criterion of local independence in terms of measurability of processes that are involved in the Doob-Meyer decomposition of stochastic processes; then we define direct and indirect influence. We propose a definition of causal influence using the concepts of a 'physical system'. This framework makes it possible to link descriptive and explicative statistical models, and encompasses quantitative processes and events. One of the features of the paper is the clear distinction between the model for the system and the model for the observation. We give a dynamical representation of a conventional joint model for human immunodeficiency virus load and CD4 cell counts. We show its inadequacy to capture causal influences whereas in contrast known mechanisms of infection by the human immunodeficiency virus can be expressed directly through a system of differential equations. Copyright (c) 2009 Royal Statistical Society.

We study the asymptotic behavior of the least squares estimators of the unknown parameters of general pth-order bifurcating autoregressive processes. Under very weak assumptions on the driven noise of the process, namely conditional pair-wise independence and suitable moment conditions, we establish the almost sure convergence of our estimators together with the quadratic strong law and the central limit theorem. All our analysis relies on non-standard asymptotic results for martingales.