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At least 937 records · Page 52Linked to original sources
PubMed1979

Studies on the dense-core vesicles in the ontogenesis of locus coeruleus. II. Method of statistical reconstruction of the diameter distribution of the dense-core vesicles.

A statistical method for reconstruction of the distribution of the diameters of spheres according to their planar image obtained from ultrathin sections, is proposed. The method can be applied for casses when the thickness of the section is commensurate with the diameter of the spheric objects studied. The formulae worked out in the work are based on the assumption that the diameters of the spheres are with discrete distribution in geometric order. The method is elaborated in connection with the problem of the changes in the diameters of the dense-core vesicles in monoaminergic structures during development.

Animals↗
PubMed2001

Phenanthrene desorption from soil in the presence of bacterial extracellular polymer: observations and model predictions of dynamic behavior.

The extracellular polymer produced by a bacterium isolated from soil was employed in laboratory studies of desorption of a model polynuelear aromatic hydrocarbon (PAH), phenanthrene. The experimental results show that the selected extracellular polymer enhances the extent of release of soil-bound phenanthrene. A kinetic model was developed as an aid in interpreting the alterations in phenanthrene desorption resulting from polymer addition. The model employs a statistical gamma (gamma) distribution to describe spectrum of rate constants for transfer of phenanthrene from soil to water, and assumes instantaneous binding of phenanthrene to polymer and of polymer to the test soil. The relevant distribution coefficients and statistical parameters of the gamma distribution needed for the model were evaluated in independent experiments. Using these measured parameters, the model provides a satisfactory independent prediction of phenanthrene release from soil to aqueous phase at two test polymer concentrations, 50 mg TOC/L and 100 mg TOC/L. The success of the independent model predictions suggests a mechanism for the influence of extracellular polymer on phenanthrene desorption. The intrinsic, soil-specific, rate constants for solid to solution transfer of phenanthrene do not appear to be changed by bacterial polymer. Instead, polymer binding of phenanthrene in solution results in an increase in driving force for desorption by decreasing the solution concentration of the free, unbound, PAH molecule.

Bacteria↗
PubMed1987

Statistical and graphical evaluation of erythrocyte volume distributions.

A protocol for the statistical and graphical evaluation of erythrocyte volume distributions has been developed using expectation-maximization methods for distribution parameter estimation. In a reference sample group of 50 healthy individuals, none of the red cell volume distributions determined by an aperture impedance method differed significantly from a log normal model. Measurements in 211 patients with anemia provided evidence that similar statistical methods could be used for the characterization of abnormal red cell volume distributions. Graphical displays accurately summarize the quantitative information derived from the analysis of volume distributions and show a reference distribution fitted to the observed distribution against the range of distributions found in healthy individuals. This protocol provides a specific, statistically valid implementation of the general principles for the analysis of cell volume distributions proposed by the International Committee for Standardization in Hematology.

Anemia↗
PubMed1988

Spatial distribution of fiber types in skeletal muscle: test for a random distribution.

A statistical test is introduced for the assessment of fiber type grouping based on the number of neighboring fibers of different histochemical type. It is conceptually simple and can be applied to regular and irregular fiber patterns alike. One important feature of this test is that it has more power than existing ones, which means that deviations from a normal situation can be detected in an earlier stage than with any other method. The dependency of the outcome of the test on type-specific size differences is rather small. Moreover, a method is given to correct for this bias. With the aid of the test it is shown that in normal muscle tissue of young persons a slight segregation of fiber type is a common situation.

Humans↗
PubMed1990

A statistical model of the VA/Q distribution.

A "blocks model" is proposed to model the distribution of the ventilation-perfusion ratio (VA/Q distribution). This model is developed from statistical principles and enables the estimated VA/Q distribution to be interpreted in a straightforward and intuitive manner. Estimation of parameters of the blocks model uses a constrained weighted least-squares procedure. Although developed initially to estimate VA/Q distributions from data generated by the multiple inert gas elimination technique (P. D. Wagner, H. A. Saltzman, and J. B. West, J. Appl. Physiol. 36: 588-599, 1974), the blocks method is applicable to any problem in which the unknown distribution is related to the data through an ill-posed integral equation and is particularly suited for problems in which the data are scarce. The method is illustrated with several examples--hypothetical data representing a wide range of VA/Q distributions as well as some real data.

Computer Simulation↗
PubMed2004

The sampling distributions of Gaussian ROC statistics.

For a discrimination experiment, a plot of the hit rate against the false-alarm rate--the ROC curve--summarizes performance across a range of confidence levels. In many content areas, ROCs are well described by a normal-distribution model and the z-transformed hit and false-alarm rates are approximately linearly related. We examined the sampling distributions of three parameters of this model when applied to a ratings procedure: the area under the ROC (Az), the normalized difference between the means of the underlying signal and noise distributions (da), and the slope of the ROC on z-coordinates (s). Statistical bias (the degree to which the mean of the sampling distribution differed from the true value) was trivial for Az, small but noticeable for da, and substantial for s. Variability of the sampling distributions decreased with the number of trials and was also affected by the number of response categories available to the participant and by the overall sensitivity level. Figures in the article and tables available on line can be used to construct confidence intervals around ROC statistics and to test statistical hypotheses.

Humans↗
PubMedDate not supplied

[Prosthetic rehabilitation with a force-distribution prosthesis. Clinical and statistical evaluation of the results obtained in 79 oral rehabilitations].

The results obtained with 79 odontoprosthetic rehabilitations by means of removable force distribution prosthesis are reported. Using half-round section wires, this prosthesis distributed masticatory forces axially on the abutment teeth and also distributes them evenly over the edentulous crest, thus achieving a mixed dental and mucous support. Clinical and statistical assessment takes in 79 patients of both sexes aged between 22 and 69 treated over the fifteen year period since 1964. All types of edentulism according to the Kennedy classification were treated. The clinical results were considered, particularly the periodontal situation and the mechanical results, above all friction between retention and function elements of the connecting wires. Clinically, 82,2% of results were positive and 74.6% of the results were mechanically positive also.

Adult↗
PubMed1995

Asymptotic distributions of polylocus test statistics.

Polylocus linkage analysis methods are modified two-point analyses which aim to approach the information gain of multilocus analysis. Terwilliger and Ott [(1992) Am J Hum Genet 51:A202, (1993) Genet Epidemiol 10:477-482] put forth two such methods. This paper presents asymptotic approximations to the null distribution of the likelihood ratio statistics for these two methods, correcting earlier reports [Terwilliger and Ott (1993) Genet Epidemiol 10:477-482; Schaid and Elston (1994) Genet Epidemiol 11:1-17]. The performance of the approximations is then assessed for finite samples of fully informative meioses.

Chromosome Mapping↗
PubMed1986

Reacting appropriately to thrombocytopenia in pregnancy.

The lower limit of normal for the platelet count is considered to be 150,000/cu mm in both pregnant and nonpregnant normal adults. In the absence of preeclampsia, sepsis, drugs, or other apparent causes, the finding of asymptomatic mild thrombocytopenia in pregnant women is compatible with previously unrecognized immune thrombocytopenic purpura (ITP). Because of the risk of fetal/neonatal thrombocytopenia and the subsequent risk of neonatal intracranial hemorrhage in infants born of mothers with ITP, the optimal mode of delivery for an asymptomatic but thrombocytopenic mother is problematic. Conceivably, those gravidas with mild previously unrecognized thrombocytopenia may not have ITP and thus could be spared cesarean section. From the platelet counts of 730 antepartum patients, we found a mean value of 263,900/cu mm with a standard deviation of 66,000/cu mm, yielding 95% confidence limits of 134,500 to 393,300/cu mm. The distribution is statistically indistinguishable from a normal distribution. Of 26 asymptomatic thrombocytopenic patients with no hematologic history, none had infants with hemorrhage or platelet counts less than 100,000/cu mm. Only one patient subsequently had severe glucocorticoid-resistant thrombocytopenia requiring splenectomy several months after delivery. The remaining patients continue to be asymptomatic to date, with platelet counts greater than 100,000/cu mm. We suggest a plan for managing less than normal platelet counts in asymptomatic gravidas without a history of hematologic abnormality.

Cesarean Section↗
PubMed2006

The mean matters: effects of statistically defined nonspeech spectral distributions on speech categorization.

Adjacent speech, and even nonspeech, contexts influence phonetic categorization. Four experiments investigated how preceding sequences of sine-wave tones influence phonetic categorization. This experimental paradigm provides a means of investigating the statistical regularities of acoustic events that influence online speech categorization and, reciprocally, reveals regularities of the sound environment tracked by auditory processing. The tones comprising the sequences were drawn from distributions sampling different acoustic frequencies. Results indicate that whereas the mean of the distributions predicts contrastive shifts in speech categorization, variability of the distributions has little effect. Moreover, speech categorization is influenced by the global mean of the tone sequence, without significant influence of local statistical regularities within the tone sequence. Further arguing that the effect is strongly related to the average spectrum of the sequence, notched noise spectral complements of the tone sequences produce a complementary effect on speech categorization. Lastly, these effects are modulated by the number of tones in the acoustic history and the overall duration of the sequence, but not by the density with which the distribution defining the sequence is sampled. Results are discussed in light of stimulus-specific adaptation to statistical regularity in the acoustic input and a speculative link to talker normalization is postulated.

Acoustic Stimulation↗
PubMedDate not supplied

[Spatial distribution of rare species: statistical approach].

Many species are locally rare (have low occurrences in a given region). The method is proposed for the analysis of spatial distribution of such species. The procedure is based on the comparison of actual mean distances between records with Monte-Carlo-simulated mean distances expected for random occurrence pattern. The method was applied to two datasets: benthic macrofauna from the Barents and Kara Seas (Kucheruk, Kotov, 2002) and the Black Sea interstitial ciliates (original data). For both datasets, the number of rare species positively correlates with number of common species per site and with the total number of species. Furthermore (and irrespectively of total diversity pattern), rare species usually were locally clumped in their distribution: each of the species was mostly found at sites that were close together. This tendency, however, was significant for the macrofauna species but not for ciliates.

Animals↗
PubMed2004

On the origin of the deviation from the first-order kinetics in inactivation of microbial cells by pulsed electric fields.

A computer model was developed for the estimation of the kinetics of microbial inactivation by pulsed electric field (PEF). The model is based on the electroporation theory of individual membrane damage, where spherical cell geometry and distribution of cell sizes are assumed. The variation of microbial cell sizes was assumed to follow a statistical probability distribution of the Gaussian type. Surviving kinetics was approximated by Weibull equation. The dependencies of two Weibull parameters (shape n and time tau, respectively) versus electric field intensity E and width of cell diameters distribution were studied.

Bacteria↗