PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “bootstrap”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed1980

Computational illustration of the bootstrap effect.

A constructive computational model is used to show that even under poor case assumptions genetic systems accumulate features which increase their amenability to evolution. These features decrease the fitness of the individual organism, but hitchhike along with the fitness-increasing traits whose probability of appearance they increase.

Biological Evolution↗
PubMed2005

Bootstrap analysis of the relation between initial adhesive events and long-term cellular functions of human osteoblasts cultured on biocompatible metallic substrates.

Classically, the evaluation of cellular adhesion of cells on substrates is limited to the evaluation of cell attachment after some hours. We have claimed for several years that this evaluation is incomplete concerning the evaluation of cell adhesion and more precisely of the quality of the in vitro cell/biomaterial interface. With a view to demonstrating this assertion, we develop in this paper statistical correlations between short-term adhesion (STA) evaluating the attachment after 24 h (IA: initial attachment) and long-term adhesion (LTA) evaluating the strength of the cell/matrix substrate interface over 21 days of culture (AP: adhesion power). Additionally, as the adhesion phase is known to influence further growth of cells we proceed to the correlation of STA with the number of cells after 21 days. We demonstrate statistically the expected positive relation existing between STA and cell growth and we show that this relation is totally independent of the substrate's surface topography or chemistry. More surprisingly, we demonstrate the absence of correlation between IA and AP. This illustrates the fact that different mechanisms underlie STA and LTA. Moreover, this study demonstrates that the evaluation of the number of attached cells after some hours cannot let us presume either that cells will survive or that they will adhere at later times by forming a complex cell/substrate interface by synthesis of extracellular matrix proteins. Finally, the originality of this work lies in the extensive statistical correlation analysis performed between biological parameters describing the cell behaviour on a substrate.

Alloys↗
PubMed2006

Bootstrap tests of significance and the case for humanlike skeletal-size dimorphism in Australopithecus afarensis.

Most estimates of sexual size dimorphism in Australopithecus afarensis indicate that this early hominin was more dimorphic than modern humans. In contrast, a recent study reported that size variation in A. afarensis, as represented by postcranial remains from Hadar and Maka, Ethiopia, is statistically most similar to that of modern humans, indicating a humanlike level of sexual dimorphism. Here, we evaluate the evidence for humanlike dimorphism in A. afarensis. We argue that statistical support for this claim is not as robust as has been asserted for the following reasons: (1) the analysis from which the claim was derived does not distinguish the A. afarensis sample from either the human or chimpanzee samples; (2) for some of the comparisons made, the A. afarensis sample cannot be distinguished from the Gorilla sample using two-tailed tests; and (3) the A. afarensis postcranial sample used in the analysis may contain more male than female specimens, which precludes a straightforward interpretation of the statistical results. Thus, support for humanlike dimorphism is equivocal, and a greater level of dimorphism cannot be ruled out.

Animals↗
PubMed2006

Bootstrapping conceptual deduction using physical connection: rethinking frontal cortex.

The age at which infants can demonstrate the ability to deduce abstract rules can be reduced by more than half, from 21 months to 9 months. The key is to introduce a physical connection between the items to be conceptually related. I argue here that making the same change in how items are presented might also help some preschoolers with learning delays, especially some children with autism. I also suggest that the roles of premotor and ventrolateral prefrontal cortices in deducing abstract rules might have been misinterpreted behaviorally and anatomically. The crucial brain region may be the periarcuate, which partially overlaps both premotor and lateral prefrontal cortex. The cognitive ability made possible by this region might be something far more elementary than previously considered: the ability to perceive conceptual connections in the absence of physical connection.

Child↗
PubMed2002

Bootstrapping the lexicon: a computational model of infant speech segmentation.

Prelinguistic infants must find a way to isolate meaningful chunks from the continuous streams of speech that they hear. BootLex, a new model which uses distributional cues to build a lexicon, demonstrates how much can be accomplished using this single source of information. This conceptually simple probabilistic algorithm achieves significant segmentation results on various kinds of language corpora - English, Japanese, and Spanish; child- and adult-directed speech, and written texts; and several variations in coding structure - and reveals which statistical characteristics of the input have an influence on segmentation performance. BootLex is then compared, quantitatively and qualitatively, with three other groups of computational models of the same infant segmentation process, paying particular attention to functional characteristics of the models and their similarity to human cognition. Commonalities and contrasts among the models are discussed, as well as their implications both for theories of the cognitive problem of segmentation itself, and for the general enterprise of computational cognitive modeling.

Algorithms↗
PubMed1995

Bootstraps taxometrics. Solving the classification problem in psychopathology.

Classification in psychopathology is a problem in applied mathematics; it answers the empirical question "Is the latent structure of these phenotypic indicator correlations taxonic (categories) or nontaxonic (dimensions, factors)?" It is not a matter of convention or preference. Two taxometric procedures, MAMBAC and MAXCOV-HITMAX, provide independent tests of the taxonic conjecture and satisfactorily accurate estimates of the taxon base rate, the latent means, and the valid and false-positive rates achievable by various cuts. The method requires no gold standard criterion, applying crude fallible diagnostic "criteria" only in the phase of discovery to identify plausible candidate indicators. Confidence in the inference to taxonic structure and numerical accuracy of latent values is provided by multiple consistency tests, hence the term coherent cut kinetics for the general approach. Further revision of diagnostic systems should be based on taxometric analysis rather than on committee decisions based on clinical impressions and nontaxometric research.

Humans↗
PubMed2004

Testing the phylogenetic position of a parasitic plant (Cuscuta, Convolvulaceae, asteridae): Bayesian inference and the parametric bootstrap on data drawn from three genomes.

Previous findings on structural rearrangements in the chloroplast genome of Cuscuta (dodder), the only parasitic genus in the morning-glory family, Convolvulaceae, were attributed to its parasitic life style, but without proper comparison to related nonparasitic members of the family. Before molecular evolutionary questions regarding genome evolution can be answered, the phylogenetic problems within the family need to be resolved. However, the phylogenetic position of parasitic angiosperms and their precise relationship to nonparasitic relatives are difficult to infer. Problems are encountered with both morphological and molecular evidence. Molecular data have been used in numerous studies to elucidate relationships of parasitic taxa, despite accelerated rates of sequence evolution. To address the question of the position of the genus Cuscuta within Convolvulaceae, we generated a new molecular data set consisting of mitochondrial (atpA) and nuclear (RPB2) genes, and analyzed these data together with an existing chloroplast data matrix (rbcL, atpB, trnL-F, and psbE-J), to which an additional chloroplast gene (rpl2) was added. This data set was analyzed with an array of phylogenetic methods, including Bayesian analysis, maximum likelihood, and maximum parsimony. Further exploration of data was done by using methods of phylogeny hypothesis testing. At least two nonparasitic lineages are shown to diverge within the Convolvulaceae before Cuscuta. However, the exact sister group of Cuscuta could not be ascertained, even though many alternatives were rejected with confidence. Caution is therefore warranted when interpreting the causes of molecular evolution in Cuscuta. Detailed comparisons with nonparasitic Convolvulaceae are necessary before firm conclusions can be reached regarding the effects of the parasitic mode of life on patterns of molecular evolution in Cuscuta.

Base Sequence↗
PubMed1994

Bootstrapping.

Explore the source record for details and available documents.

Cross Infection↗
PubMed1992

Inference of horizontal genetic transfer from molecular data: an approach using the bootstrap.

Inconsistencies in taxonomic relationships implicit in different sets of nucleic acid sequences potentially result from horizontal transfer of genetic material between genomes. A nonparametric method is proposed to determine whether such inconsistencies are statistically significant. A similarity coefficient is calculated from ranked pairwise identities and evaluated against a distribution of similarity coefficients generated from resampled data. Subsequent analyses of partial data sets, obtained by the elimination of individual taxa, identify particular taxa to which the significance may be attributed, and can sometimes help in distinguishing horizontal genetic transfer from inconsistencies due to convergent evolution or variation in evolutionary rate. The method was successfully applied to data sets that were not found to be significantly different with existing methods that use comparisons of phylogenetic trees. The new statistical framework is also applicable to the inference of horizontal transfer from restriction fragment length polymorphism distributions and protein sequences.

Animals↗