Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Statistical Distributions”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,153 records · Page 64Linked to original sources
PubMed2004

Frequency and spatial distribution of environmental Campylobacter spp.

Humans are exposed to Campylobacter spp. in a range of sources via both food and environmental pathways. For this study, we explored the frequency and distribution of thermophilic Campylobacter spp. in a 10- by 10-km square rural area of Cheshire, United Kingdom. The area contains approximately 70, mainly dairy, farms and is used extensively for outdoor recreational activities. Campylobacter spp. were isolated from a range of environmental samples by use of a systematic sampling grid. Livestock (mainly cattle) and wildlife feces and environmental water and soil samples were cultured, and isolates were presumptively identified by standard techniques. These isolates were further characterized by PCR. Campylobacter jejuni was the most prevalent species in all animal samples, ranging from 11% in samples from nonavian wildlife to 36% in cattle feces, and was isolated from 15% of water samples. Campylobacter coli was commonly found in water (17%) and sheep (21%) samples, but rarely in other samples. Campylobacter lari was recovered from all sample types, with the exception of sheep feces, and was found in moderate numbers in birds (7%) and water (5%). Campylobacter hyointestinalis was only recovered from cattle (7%) and birds (1%). The spatial distribution and determinants of C. jejuni in cattle feces were examined by the use of model-based spatial statistics. The distribution was consistent with very localized within-farm or within-field transmission and showed little evidence of any larger-scale spatial dependence. We concluded that there is a potentially high risk of human exposure to Campylobacter spp., particularly C. jejuni, in the environment of our study area. The prevalence and likely risk posed by C. jejuni-positive cattle feces in the environment diminished as the fecal material aged. After we took into account the age of the fecal material, the absence or presence of rain, and the presence of bird feces, there was evidence of significant variation in the prevalence of C. jejuni-positive cattle feces between grazing fields but no evidence of spatial clustering beyond this resolution. The spatial pattern of C. jejuni is therefore consistent with that for an organism that is ubiquitous in areas contaminated with cattle feces, with a short-scale variation in infection intensity that cannot be explained solely by variations in the age of the fecal material. The observed pattern is not consistent with large-scale transmission attributable to watercourses, wildlife territories, or other geographical features that transcend field and farm boundaries.

Animals↗
PubMed2001

The estimation of statistical parameters for local alignment score distributions.

The distribution of optimal local alignment scores of random sequences plays a vital role in evaluating the statistical significance of sequence alignments. These scores can be well described by an extreme-value distribution. The distribution's parameters depend upon the scoring system employed and the random letter frequencies; in general they cannot be derived analytically, but must be estimated by curve fitting. For obtaining accurate parameter estimates, a form of the recently described 'island' method has several advantages. We describe this method in detail, and use it to investigate the functional dependence of these parameters on finite-length edge effects.

Algorithms↗
PubMed2003

Three-dimensional reconstruction of immunolabeled neuromuscular junctions in the human thyroarytenoid muscle.

OBJECTIVES/HYPOTHESIS: The objective was to reveal the location of the neuromuscular junctions in a three-dimensional reconstruction of the human thyroarytenoid muscle within the true vocal fold. STUDY DESIGN: Immunohistochemical analysis of serially sectioned human true vocal folds was performed, followed by reconstruction in three dimensions using computer imaging software. METHODS: Six fresh human larynges from autopsy were harvested, fixed in formalin, and embedded in paraffin. Eight vocal cords were studied from these six larynges. Five-micron serial sections were collected throughout the entire vocal cord in an axial plane at 500-microm intervals. Immunohistochemical analysis was performed with anti-synaptophysin antibody. A computer-controlled imaging and reconstruction system was used to create a three-dimensional reconstruction from the serial sections and to represent the location of the clustered band of neuromuscular junctions within each true vocal fold. The vocal cord was divided into equal thirds from anterior to posterior for statistical analysis. RESULTS: The most neuromuscular junctions (74%) were located in the middle third, and the least (7%) were found in the anterior third. The difference in anterior-to-posterior distribution was statistically significant in all eight specimens by chi2 analysis (P <.001). CONCLUSION: The distribution of neuromuscular junctions is not random within the human thyroarytenoid muscle. Because neuromuscular junctions are most highly concentrated in a band within the mid belly of the muscle, botulinum toxin type A (Botox) injection in patients with spasmodic dysphonia should be targeted to this region.

Adult↗
PubMed2005

Pressures generated during spinal manipulation and their association with hand anatomy.

BACKGROUND CONTEXT: The role of the variation in the application manipulation itself is largely unknown. A greater understanding of its input parameters is necessary to better understand spinal manipulation outcomes. PURPOSE: The objective of this study is to determine if pressures generated during manipulation are altered by hand configuration. DESIGN/SETTING: Paired comparison of 2 different variable groups. METHODS: Sixteen chiropractors provided 2 manipulations to a rigid surface using 2 hand configurations used commonly in clinical practice: arched and flat. Interposed between the hand and the rigid surface was a pressure sensor array and radiographic cassette. For each manipulation, pressures were recorded and a radiographic image was captured. Two radiologists then located the osseous features of the hand with respect to the sensor array. RESULTS: In 15 of 16 cases, arched configurations produced peak pressures that corresponded to the radiographic location of the pisiform bone. In flat configurations, peak pressure migrated about the location of the hamate bone. Radiologists' agreement for bone position was high (kappa = 0.96). Measures of peak pressure, total pressure, and pressure distribution were statistically different between hand configurations. CONCLUSIONS: The results of this study suggest that hand configuration influences the magnitude, location, and distribution of pressure generated by the hand during manipulation. This knowledge may have importance in understanding the relation among application parameters of manipulation, therapeutic benefit, and patient safety.

Adult↗
PubMed2000

CNV and temporal uncertainty with 'ageing' and 'non-ageing' S1-S2 intervals.

OBJECTIVES: Uncertainty about the timing of a known external event is an everyday phenomenon but has been rarely investigated with electrophysiological methods. We studied how the amplitude of the contingent negative variation (CNV) is affected by temporal variation of S2 presentation. Competing hypotheses about the development of CNV during the foreperiod until S2 presentation were that CNV either would follow a monotonic trend, be it increasing or decreasing, or alternatively that the time-course of CNV would be affected by the probability with which S2 was presented at each time-point in a given task. METHODS: The interval between cueing stimulus and imperative stimulus was randomly chosen from 3 different values between 1.3 and 2.6 s, using 3 different probability distributions in separate blocks: an 'ageing', a 'non-ageing' and a 'Gaussian' distribution. RESULTS: As previously shown, reaction times were determined by the probability of the imperative stimulus at the given length of the foreperiod. The same was found for CNV amplitude: the effects of temporal uncertainty on CNV mainly depended on the particular distribution of temporal probabilities used in a block. The relevant parameter was the a posteriori probability of event occurrence, very similar to the effects of this parameter on response times. In fact, the major part of the effect of a posteriori probability on CNV was common variation of CNV and response times. CONCLUSIONS: Thus, under temporal uncertainty the amplitude of CNV reflects the subjective expectancies for the occurrence of a given event, with this variation being related to variations in response times.

Adult↗
PubMed1996

The frequency distribution of blood-flow velocities in the extraocular vessels.

PURPOSE: The study was carried out in order to assess the distribution of normal values of the blood-flow velocity in the extraocular vessels. METHODS: In 240 healthy visitors to a public fair, blood-flow characteristics in the extraocular vessels were measured, and the resistivity index was calculated. Blood-flow velocity was measured with a color Doppler imaging device, using a 7.5-mHz linear-array transducer. Peak-systolic and end-diastolic blood-flow velocities in the arteries were measured, and the resistivity index was calculated. In the central retinal vein the minimal and maximal blood-flow velocities were measured. The statistical analysis of the 14 measured and calculated variables included descriptive statistics, frequency distribution, and quantile plots. RESULTS: The quantile plots of the cumulative frequency showed that none of these 14 variables are normally distributed. Also, no normal distribution could be achieved by adjustment of the data by age. CONCLUSIONS: The blood-flow velocities in the extraocular vessels measured are not distributed normally. Therefore, nonparametric tests are to be used for statistical analysis if the sample size is small. The estimation of tolerance intervals has to be based on distribution-free assumptions.

Adolescent↗
PubMed1967

Dynamic statistics of crayfish caudal photoreceptors.

Crayfish caudal photoreceptor units were monitored during transient and steady-state responses to light stimuli (step on, step off). A statistical analysis of interpulse interval distributions during quasi-stationary time periods was carried out. Firing statistics during transient conditions were superposable with statistics under whatever steady stimulation produced the same firing rate, indicating that mean firing rate is a sufficient statistic. Distributions encountered formed a continuum of possible shapes. Considerable variation in shape was found with temperature and also among species, with Orconectes clarkii tending to fire more regularly than Orconectes virilis. Some properties of O. virilis statistics are described, including a linear relation between mean and standard deviation, and a tendency for intervals to be nonindependent. The data are considered as constraints on closed form models of the photoreceptor nerve pulse generator.

Animals↗
PubMedDate not supplied

Estimating ethnic change in London, 1981-91, using a variety of census data.

"This paper provides estimates of ethnic minority populations in 1981 in Greater London so that spatial population change can be measured. The estimation method involves the application of conditional probabilities of ethnicity given the country of birth. Several different data sources from the census of population have been used to compute the conditional probabilities. Each of these sources has deficiencies; the new method proposed here employs data on 1981-91 survivors in the ONS Longitudinal Study (LS). The estimated ethnic minority populations for 1981 are smaller than those generated using 1991 Census data, and hence the estimate of change is larger. Careful pairwise comparisons are made between alternative estimates. A set of very different maps of change, based on the LS method, are presented and interpreted for the ethnic groups of London at the borough scale."

Culture↗
PubMed2001

Improved inference of mutation rates: II. Generalization of the Luria-Delbrück distribution for realistic cell-cycle time distributions.

In the first paper of this series (Kepler and Oprea, Theor. Popul. Biol. 2001) we found a continuum approximation of the Luria-Delbrück distribution in terms of a scaled variable related to the proportion of mutants in the culture. Here we show that the Luria-Delbrück distribution is inaccurate when realistic division processes are being considered due to the non-Markovian character of the cell cycle. We derive the expectation of the proportion of mutants in the culture for arbitrary cell-cycle time distributions. We then introduce a two-parameter generalization of the continuum Luria-Delbrück distribution for two of the more commonly used cell-cycle time distributions: gamma and shifted exponential. We obtain the generalized distribution by defining a map from the actual parameters to "effective" parameters. The effective mutation rate is obtained analytically, while the effective population size is obtained by fitting simulation data. Our simulations show that the second parameter depend mostly on the coefficient of variation of the cell-cycle time distribution.

Algorithms↗
PubMed1999

Quantum kinetics and thermalization in a particle bath model.

We study the dynamics of relaxation and thermalization in an exactly solvable model of a particle interacting with a harmonic oscillator bath. Our goal is to understand the effects of non-Markovian processes on the relaxational dynamics and to compare the exact evolution of the distribution function with approximate Markovian and non-Markovian quantum kinetics. There are two different cases that are studied in detail: (i) a quasiparticle (resonance) when the renormalized frequency of the particle is above the frequency threshold of the bath and (ii) a stable renormalized "particle" state below this threshold. The time evolution of the occupation number for the particle is evaluated exactly using different approaches that yield to complementary insights. The exact solution allows us to investigate the concept of the formation time of a quasiparticle and to study the difference between the relaxation of the distribution of bare particles and that of quasiparticles. For the case of quasiparticles, the exact occupation number asymptotically tends to a statistical equilibrium distribution that differs from a simple Bose-Einstein form as a result of off-shell processes whereas in the stable particle case, the distribution of particles does not thermalize with the bath. We derive a non-Markovian quantum kinetic equation which resums the perturbative series and includes off-shell effects. A Markovian approximation that includes off-shell contributions and the usual Boltzmann equation (energy conserving) are obtained from the quantum kinetic equation in the limit of wide separation of time scales upon different coarse-graining assumptions. The relaxational dynamics predicted by the non-Markovian, Markovian, and Boltzmann approximations are compared to the exact result. The Boltzmann approach is seen to fail in the case of wide resonances and when threshold and renormalization effects are important.

Journal Article↗
PubMed1999

A joint interspike interval difference stochastic spike train analysis: detecting local trends in the temporal firing patterns of single neurons.

We introduce a stochastic spike train analysis method called joint interspike interval difference (JISID) analysis. By design, this method detects changes in firing interspike intervals (ISIs), called local trends, within a 4-spike pattern in a spike train. This analysis classifies 4-spike patterns that have similar incremental changes. It characterizes the higher-order serial dependence in spike firing relative to changes in the firing history. Mathematically, this spike train analysis describes the statistical joint distribution of consecutive changes in ISIs, from which the serial dependence of the changes in higher-order intervals can be determined. It is similar to the joint interspike interval (JISI) analysis, except that the joint distribution of consecutive ISI differences (ISIDs) is quantified. The graphical location of points in the JISID scatter plot reveals the local trends in firing (i.e., monotonically increasing, monotonically decreasing, or transitional firing). The trajectory of these points in the serial-JISID plot traces the time evolution of these trends represented by a 5-spike pattern, while points in the JISID scatter plot represent trends of a 4-spike pattern. We provide complete theoretical interpretations of the JISID analysis. We also demonstrate that this method indeed identifies firing trends in both simulated spike trains and spike trains recorded from cultured neurons.

Animals↗