Biomedical subjects

A Almudevar

Publications and source records attributed to A Almudevar.

3 recordsLinked to original sources

PubMed2005

Peak oxygen uptake and mortality in children with cystic fibrosis.

BACKGROUND: Single measurements of peak oxygen uptake (VO2) have been shown to predict mortality in patients with cystic fibrosis (CF) although no longitudinal study of serial measurements has been reported in children. A study was undertaken to determine whether the initial, final, or the rate of fall of forced expiratory volume in 1 second (FEV1) or peak VO2 was a better predictor of mortality. METHODS: Twenty eight children aged 8-17 years with CF performed annual pulmonary function and maximal exercise tests over a 5 year period to determine FEV1 and peak VO2, magnitude of their change over time, and survival over the subsequent 7-8 years. Analysis was done using Kaplan-Meier curves and Cox proportional hazard model. RESULTS: Peak VO2 fell during the observation period in 70% of the patients, with a mean annual decline of 2.1 ml/min/kg. Initial peak VO2 was not predictive of mortality but rate of decline and final peak VO2 of the series were significant predictors. Patients with peak VO2 less than 32 ml/min/kg exhibited a dramatic increase in mortality, in contrast to those whose peak VO2 exceeded 45 ml/min/kg, none of whom died. The first, last, and rate of decline in FEV1 over time were all significant predictors of mortality. CONCLUSIONS: Higher peak VO2 is a marker for longer survival in CF patients.

Adolescent↗

PubMed2001

A bootstrap assessment of variability in pedigree reconstruction based on genetic markers.

The problem of assessing the variability in pedigree reconstruction using DNA markers is considered for the special case of single generation samples with no parents present. Error in pedigree reconstruction is measured through a metric imposed on the space of partitions of the individuals into family groups. A confidence set can therefore be taken to be a neighborhood of a point estimate, analogous to the estimation of a parameter in Euclidean space. The coverage probability is estimated using bootstrap techniques. Although the distributional properties of the sample depend on the population genotype frequencies, these are in practice usually unknown. Confidence sets conditioned on a statistic approximately sufficient for these frequencies are compared with confidence sets obtained by substituting frequency estimates directly into the sampling distribution. In two simulation studies, the difference is found to be of some consequence.

Animals↗

PubMed2001

Most powerful permutation invariant tests for relatedness hypotheses using genotypic data.

The problem of inferring kinship structure among a sample of individuals using genetic markers is considered with the objective of developing hypothesis tests for genetic relatedness with nearly optimal properties. The class of tests considered are those that are constrained to be permutation invariant, which in this context defines tests whose properties do not depend on the labeling of the individuals. This is appropriate when all individuals are to be treated identically from a statistical point of view. The approach taken is to derive tests that are probably most powerful for a permutation invariant alternative hypothesis that is, in some sense, close to a null hypothesis of mutual independence. This is analagous to the locally most powerful test commonly used in parametric inference. Although the resulting test statistic is a U-statistic, normal approximation theory is found to be inapplicable because of high skewness. As an alternative it is found that a conditional procedure based on the most powerful test statistic can calculate accurate significance levels without much loss in power. Examples are given in which this type of test proves to be more powerful than a number of alternatives considered in the literature, including Queller and Goodknight's (1989) estimate of genetic relatedness, the average number of shared alleles (Blouin, 1996), and the number of feasible sibling triples (Almudevar and Field, 1999).

Alleles↗