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Analytical Power (analytical + power)
Selected AbstractsEstimating the power of variance component linkage analysis in large pedigreesGENETIC EPIDEMIOLOGY, Issue 6 2006Wei-Min Chen Abstract Variance component linkage analysis is commonly used to map quantitative trait loci (QTLs) in general pedigrees. Large pedigrees are especially attractive for these studies because they provide greater power per genotyped individual than small pedigrees. We propose accurate and computationally efficient methods to calculate the analytical power of variance component linkage analysis that can accommodate large pedigrees. Our analytical power computation involves the approximation of the noncentrality parameter for the likelihood-ratio test by its Taylor expansions. We develop efficient algorithms to compute the second and third moments of the identical by descent (IBD) sharing distribution and enable rapid computation of the Taylor expansions. Our algorithms take advantage of natural symmetries in pedigrees and can accurately analyze many large pedigrees in a few seconds. We verify the accuracy of our power calculation via simulation in pedigrees with 2,5 generations and 2,8 siblings per sibship. We apply this proposed analytical power calculation to 98 quantitative traits in a cohort study of 6,148 Sardinians in which the largest pedigree includes 625 phenotyped individuals. Simulations based on eight representative traits show that the difference between our analytical estimation of the expected LOD score and the average of simulated LOD scores is less than 0.05 (1.5%). Although our analytical calculations are for a fully informative marker locus, in the settings we examined power was similar to what could be attained with a single nucleotide polymorphism (SNP) mapping panel (with >1 SNP/cM). Our algorithms for power analysis together with polygenic analysis are implemented in a freely available computer program, POLY. Genet. Epidemiol. 2006. © 2006 Wiley-Liss, Inc. [source] Imputation of SF-12 Health Scores for Respondents with Partially Missing DataHEALTH SERVICES RESEARCH, Issue 3 2005Honghu Liu Objective. To create an efficient imputation algorithm for imputing the SF-12 physical component summary (PCS) and mental component summary (MCS) scores when patients have one to eleven SF-12 items missing. Study Setting. Primary data collection was performed between 1996 and 1998. Study Design. Multi-pattern regression was conducted to impute the scores using only available SF-12 items (simple model), and then supplemented by demographics, smoking status and comorbidity (enhanced model) to increase the accuracy. A cut point of missing SF-12 items was determined for using the simple or the enhanced model. The algorithm was validated through simulation. Data Collection. Thirty-thousand-three-hundred and eight patients from 63 physician groups were surveyed for a quality of care study in 1996, which collected the SF-12 and other information. The patients were classified as "chronic" patients if they reported that they had diabetes, heart disease, asthma/chronic obstructive pulmonary disease, or low back pain. A follow-up survey was conducted in 1998. Principal Findings. Thirty-one percent of the patients missed at least one SF-12 item. Means of variance of prediction and standard errors of the mean imputed scores increased with the number of missing SF-12 items. Correlations between the observed and the imputed scores derived from the enhanced models were consistently higher than those derived from the simple model and the increments were significant for patients with ,6 missing SF-12 items (p<.03). Conclusion. Missing SF-12 items are prevalent and lead to reduced analytical power. Regression-based multi-pattern imputation using the available SF-12 items is efficient and can produce good estimates of the scores. The enhancement from the additional patient information can significantly improve the accuracy of the imputed scores for patients with ,6 items missing, leading to estimated scores that are as accurate as that of patients with <6 missing items. [source] The effects of muscular dystrophy on the craniofacial shape of Mus musculusJOURNAL OF ANATOMY, Issue 6 2007Donna Carlson Jones Abstract Skeletal anomalies are common in patients with muscular dystrophy, despite an absence of mutations to genes that specifically direct skeletogenesis. In order to understand these anomalies further, we examined two strains of muscular dystrophy (laminin- and merosin-deficient) relative to controls, to determine how the weakened muscle forces affected skull shape in a mouse model. Shape was characterized with geometric morphometric techniques, improving upon the limited analytical power of the standard linear measurements. Through these techniques, we document the specific types of cranial skeletal deformation produced by the two strains, each with individual shape abnormalities. The mice with merosin deficiency (with an earlier age of onset) developed skulls with more deformation, probably related to the earlier ontogenetic timing of disease onset. Future examinations of these mouse models may provide insight regarding the impact of muscular forces and the production and maintenance of craniofacial integration and modularity. [source] The design of a multi-dimensional LC-SPE-NMR system (LC2 -SPE-NMR) for complex mixture analysis,MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2006A. J. Alexander Abstract In this communication, we describe the design of an online multi-chromatographic approach to the routine NMR analyses of low-level components (,0.1%) in complex mixtures. The technique, termed LC2 -SPE-NMR, optimally combines multi-dimensional liquid chromatography with SPE technology for isolating, enriching and delivering trace analytes to the NMR probe. The fully automated LC2 -SPE-NMR system allows for maximal loading capacity (in the first, preparative LC dimension), close to optimal peak resolution (in the second, analytical LC dimension) and enhanced sample concentration (through SPE). Using this system, it is feasible to conveniently conduct a wide range of NMR experiments on, for example, drug impurities at the low microgram per milliliter level, even for components poorly resolved in the first dimension. Such a sensitivity gain significantly elevates the analytical power of online NMR technology in terms of the level at which substances of pharmaceutical significance can be structurally characterized. Copyright © 2006 John Wiley & Sons, Ltd. [source] Deep genetic subdivision within a continuously distributed and highly vagile marine mammal, the Steller's sea lion (Eumetopias jubatus)MOLECULAR ECOLOGY, Issue 10 2006J. I. HOFFMAN Abstract The Steller's sea lion Eumetopias jubatus is an endangered marine mammal that has experienced dramatic population declines over much of its range during the past five decades. Studies using mitochondrial DNA (mtDNA) have shown that an apparently continuous population includes a strong division, yielding two discrete stocks, western and eastern. Based on a weaker split within the western stock, a third Asian stock has also been defined. While these findings indicate strong female philopatry, a recent study using nuclear microsatellite markers found little evidence of any genetic structure, implying extensive paternal gene flow. However, this result was at odds with mark,recapture data, and both sample sizes and genetic resolution were limited. To address these concerns, we increased analytical power by genotyping over 700 individuals from across the species' range at 13 highly polymorphic microsatellite loci. We found a clear phylogenetic break between populations of the eastern stock and those of the western and Asian stocks. However, our data provide little support for the classification of a separate Asian stock. Our findings show that mtDNA structuring is not due simply to female philopatry, but instead reflects a genuine discontinuity within the range, with implications for both the phylogeography and conservation of this important marine mammal. [source] Species-specific detection of Lobaria pulmonaria (lichenized ascomycete) diaspores in litter samples trapped in snow coverMOLECULAR ECOLOGY, Issue 9 2001J.-C. Walser Abstract The foliose lichen Lobaria pulmonaria has suffered a substantial decline in central and northern Europe during the twentieth century and is now considered to be critically endangered in many European lowland regions. Based on demographic studies, it has been proposed that under the present environmental conditions and forest management regimes, dispersal of diaspores and subsequent establishment of new thalli are insufficient to maintain the remnant small lowland populations. Chances of long-term survival may therefore be reduced. The data and analytical power of these demographic studies are limited. Since lichen diaspores show very few species-specific morphological characteristics, and are therefore almost indistinguishable, the accurate assessment of diaspore flux would be a fundamental first step in better understanding the life cycle of L. pulmonaria. Here we present a new molecular approach to investigate the dispersal of L. pulmonaria diaspores in its natural environment by specifically identifying small amounts of DNA in snow litter samples at varying distances from known sources. We used a species-specific polymerase chain reaction (PCR) primer pair to amplify the ribosomal internal transcribed spacer region (ITS rDNA) and a sensitive automated PCR product detection system using fluorescent labelled primers. We detected considerable amounts of naturally dispersed diaspores, deposited as far as 50 m away from the closest potential source. Diaspores were only found in the direction of the prevailing wind. Diaspore deposition varied from 1.2 diaspores per m2 per day at 50 m distance from the source to 15 diaspores per m2 per day at 1 m distance. The method described in this paper opens up perspectives for studies of population dynamics and dispersal ecology mainly in lichenized ascomycetes but also in other organisms with small, wind-dispersed diaspores. [source] A Content Analysis of Risk Management Disclosures in Canadian Annual ReportsCANADIAN JOURNAL OF ADMINISTRATIVE SCIENCES, Issue 2 2005Kaouthar Lajili Abstract This research paper examines risk information disclosures in Canadian annual reports to provide insights into the current risk disclosure environment, its characteristics, and the analytical usefulness of the information disclosed to the firm's stakeholders. Following a content analysis, the authors describe and then analyze in greater detail the subject matter of risk disclosures of TSE 300 Canadian companies by summarizing and classifying disclosed risk-related information. Results show a high degree of risk disclosure intensity reflecting both mandatory and voluntary risk management disclosures. However, the analytical power of such disclosures, as captured by the risk assessment analysis, appears to lack uniformity, clarity, and quantification, thus potentially limiting their usefulness. The authors conclude that more formalized and comprehensive risk disclosures might be desirable in the future to effectively reduce information asymmetries between management and stakeholders. Résumé La présente étude analyse les divulgations d'informations sur le risque dans les rapports annuels canadiens. Elle se propose de jeter une lumière sur l'environnement actuel de divulgation des risques, ses caractéristiques, et l'utilité analytique des informations divulguées pour les acteurs de l'industrie canadienne. Grâce à la méthode de l'analyse du contenu, les auteurs décrivent puis analysent de fa,on plus détaillée le contenu actuel des divulgations d'informations sur le risque des entreprises du TSE 300. Ils y parviennent en synthétisant et en catégorisant les informations divulguées. Les résultats montrent que les divulgations se font à une fréquence assez élevée, consécutive aux divulgations obligatoires et volontaires de gestion des risques. Cependant, vu la manière dont l'analyse d'évaluation des risques divulgue ces informations, leur pouvoir analytique semble manquer d'homogénéité, de clarté, et de quantification, ce qui limite potentiellement leur utilité. Les auteurs concluent qu'à l'avenir, les divulgations de risques gagneraient à être plus formalisées et plus complètes. Ceci permettrait de réduire l'asymétrie des informations entre les gestionnaires des risques et les investisseurs. [source] | ||||||||||