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At least 145 records · Page 8Linked to original sources
PubMed1992

Analysis of body-length distribution of Dirofilaria immitis in the cardio-pulmonary blood vessel of naturally infected dogs in Shiga Prefecture, Japan.

Body-length frequencies of Dirofilaria immitis collected from the cardio-pulmonary blood vessel of the dogs were studied in Shiga Prefecture. Japan, in October 1983 and in January and May 1984. The frequencies were not distributed normally because they included the populations of shorter-bodied worms, probably the growing younger worms, whereas the distributions of the body length of worms collected in July 1983 were proved to fit the single normal distribution. From the results of body-length distribution analysis, the worms collected in different seasons were each composed of 1 to 3 groups with different mean body-lengths, standard deviations and composition rates and successive changes were observed in the distribution patterns. According to the analysis of population structures, the infective season was estimated to range from April or May to October or November in 1983 from the respective ages of shorter-bodied worm groups. The annual rates of first infection and re-infection in 1983 determined by the population of shorter-bodied females collected in January were 48% and 93% respectively and the number of newly infecting females per dog ranged from 1 to 27 with a geometric mean of 8.5. The numbers of newly infecting female worms were distributed following the negative binomial and Poisson distributions in newly infected and already infected dogs respectively.

Animals↗
PubMed1986

The natural variability of vital rates and associated statistics.

The first concern of this work is the development of approximations to the distributions of crude mortality rates, age-specific mortality rates, age-standardized rates, standardized mortality ratios, and the like for the case of a closed population or period study. It is found that assuming Poisson birthtimes and independent lifetimes implies that the number of deaths and the corresponding midyear population have a bivariate Poisson distribution. The Lexis diagram is seen to make direct use of the result. It is suggested that in a variety of cases, it will be satisfactory to approximate the distribution of the number of deaths given the population size, by a Poisson with mean proportional to the population size. It is further suggested that situations in which explanatory variables are present may be modelled via a doubly stochastic Poisson distribution for the number of deaths, with mean proportional to the population size and an exponential function of a linear combination of the explanatories. Such a model is fit to mortality data for Canadian females classified by age and year. A dynamic variant of the model is further fit to the time series of total female deaths alone by year. The models with extra-Poisson variation are found to lead to substantially improved fits.

Age Factors↗
PubMed1984

Non-random distribution of intraepithelial lymphoid cells in follicle-associated epithelium of Peyer's patches in mice.

The spatial distribution of intraepithelial lymphoid cells in follicle-associated and villus epithelium within Peyer's patches was studied quantitatively in Balb/C and CFW/L1 mice. The results were essentially the same for both strains. The distribution of the number of lymphoid cells per segmental length (equal to an average width of an epithelial cell) of dome epithelium was found to be non-random, since it deviated significantly from the theoretical Poisson distribution. Some segments of the dome epithelium, therefore, are lymphocyte-rich and some are lymphocyte-depleted, i.e. they contain either more, or less lymphoid cells than expected from the random distribution. This was in contrast to the distribution in the epithelial layer of the villi, in which the distribution of the number of lymphoid cells per segment followed the Poisson distribution. It was also demonstrated that segments rich in lymphocytes in the dome epithelium occurred in series or clusters. Lymphoid cell clustering was not observed in the villus epithelium. Possible mechanisms responsible for the non-random spatial distribution of lymphoid cells within the dome epithelium of the mouse Peyer's patches are discussed.

Animals↗
PubMed1986

Autoradiographic studies of chromosome replication during the cell cycle of Streptococcus faecium.

Analysis of the distribution of autoradiographic grains around cells of Streptococcus faecium which had been either continuously or pulse-labeled with tritiated thymidine (mass doubling time, 90 min) showed a non-Poisson distribution even when the distribution of cell sizes in the populations studied was taken into account. These non-Poisson distributions of grains were assumed to reflect the discontinuous nature of chromosome replication. To study this discontinuous process further, we fitted an equation to the grain distribution observed for the pulse-labeled cells that assumed that in any population of cells there were subpopulations in which there were zero, one, or two replicating chromosomes. This analysis predicted an average time for chromosome replication and for the period between completion of rounds of chromosome replication and division of 55 and 43 min, respectively, which were in excellent agreement with estimates made by other techniques. The present investigation extended past studies in indicating that the initiation and completion of rounds of chromosome replication are poorly phased with increases in cell volume and that the amount of chromosome replication may be different in different cell halves.

Autoradiography↗
PubMed1995

The frequencies of disease names with the natural language used in the hospital information system.

The statistical behavior of disease names referred by physicians with the natural language in a large hospital information system is little known despite the theoretical and practical interest. To address this issue, we reviewed and investigated the usage-frequencies of 18,274 disease names, 10,288 for outpatient care and 7986 for inpatient care, referred from October 1983 to June 1992 with the notation of the natural language in Japanese by the use of the registration-retrieval system of disease names at Fukui Medical School, Japan. Consequently, we found that the investigated distributions did not conform to the Poisson distribution, but conformed well to the Polya-Eggenberger distribution in both cases of outpatient and inpatient care. It implies that the disease names with the natural language are possibly referred by physicians with some interrelations.

Disease↗
PubMed1998

A general theory of the sampling process with applications to the "veil line".

When a community of species is sampled, nonappearing species are not those with abundances that fall shy of some arbitrary mark, the "veil line" proposed by E. F. Preston in 1948 (Ecology 29, 254-283). Instead, they follow a hypergeometric distribution, which has no resemblance to the veil line. There is therefore no justification for the truncation of distributions proposed to describe the abundances of species in natural communities. The mistake of the veil line points to the need for a general theory of sampling. If a community has a distribution g of species abundances and if samples taken of the community tend to follow distribution f, what is the relationship of f to g? The seeds of such a theory are available in the work of E. C. Pielou. Using the Poisson distribution as a close approximation to the hypergeometric, one may immediately write and (in most cases) solve the transformation from g to f. The transformation appears to preserve distribution formulas to within constants and parameters, providing yet another reason to rule out the use of truncation. Well beyond this application, the theory provides a foundation for rethinking the sampling process and its implications for ecology.

Animals↗
PubMed1980

Ranking of glucocorticoid creams and ointments.

20 corticosteroids ointments and 19 corticosteroid creams available on the Swedish market in January 1977 were tested for their blanching effect. Three ointments and three creams showing pronounced blanching were tested only without occlusion. Hydrocortisone preparations were tested only with occlusion. Other preparations were tested with and without occlusion. All ointments and creams were tested at four randomized sites on the flexor aspect of the forearm in each of 11 or 12 subjects. When used occlusion was applied for 6 hours. Repeated readings were made, using scores 0, 1, 2, and 3. The reading at the time when most preparations showed blanching were analysed statistically. The scores for blanching showed a Poisson distribution when the mean score was less than or equal to 1. Classification of preparations according to blanching was facilitated by the fact that statistical methods for Poisson distribution could be used. A ranking of corticosteroids based on vasoconstriction was obtained, and four different groups for ointments and four for creams emerged. The arbitrary nature of any ranking and grouping of steroids is evident from the data presented.

Administration, Topical↗
PubMed1986

Sensitivity of neurons in the auditory midbrain of the grassfrog to temporal characteristics of sound. II. Stimulation with amplitude modulated sound.

The coding of fine-temporal structure of sound, especially of frequency of amplitude modulation, was investigated on the single-unit level in the auditory midbrain of the grassfrog. As stimuli sinusoidally amplitude modulated sound bursts and continuous sound with low-pass Gaussian noise amplitude modulation have been used. Both tonal and wideband noise carriers have been applied. The response to sinusoidally amplitude modulated sound bursts was studied in two aspects focussing on two types of possible codes: a rate code and a synchrony code. From the iso-intensity rate histogram five basic average response characteristics as function of modulation frequency have been observed: low-pass, band-pass, high-pass, bimodal and non-selective types. The synchronization capability, expressed in a synchronization index, was non-significant for 38% of the units and a low-pass function of modulation frequency for most of the other units. The stimulus-response relation to noise amplitude modulated sound was investigated by a non-linear system theoretical approach. On the basis of first- and second-order Wiener-Volterra kernels possible neural mechanisms accounting for temporal selectivity were obtained. About one quarter of the units had response characteristics that were invariant to changes in sound pressure level and spectral content of the carrier. These units may function as feature detectors of fine-temporal structure of sound. The spectro-temporal sensitivity range of the auditory midbrain of the grassfrog appeared not to be restricted to and showed no preference for the spectro-temporal characteristics of the ensemble of conspecific calls. Comparison of response characteristics to periodic click trains as studied in the companion paper (Epping and Eggermont, 1986) and sinusoidally amplitude modulated sound bursts revealed that the observed temporal sensitivity is due to a combination of sensitivities to sound periodicity and pulse duration. It was found that for most units the first-order kernels for Gaussian amplitude modulated stimuli and Poisson distributed click stimuli were alike. In contrast second-order kernels for the Gaussian amplitude modulated stimuli often represented only static non-linearities, while second-order kernels for Poisson distributed clicks (Epping and Eggermont, 1986) mostly revealed dynamic non-linearities.

Acoustic Stimulation↗
PubMed1988

Induced and natural break sites in the chromosomes of Hawaiian Drosophila.

gamma-Irradiation of a laboratory strain of the Hawaiian species Drosophila heteroneura yielded 310 breaks in the five major acrocentric polytene chromosomes. Their map positions conform to the Poisson distribution, unlike most of the 436 natural breaks mapped in 105 closely related species endemic to Hawaii. Genome element E is longer and has more induced breaks than the others. Both in Hawaiian and related species groups, this element shows increased polymorphism and fixation of naturally occurring inversions. The X chromosome (element A) also accumulates many natural breaks; the majority of the resulting aberrations become fixed rather than remain as polymorphisms. Although size may play a small role in initial break distribution, the major effects relative to the establishment of a rearrangement in natural populations are ascribed to the interaction of selection and drift. Nonconformance of the natural breaks to the Poisson distribution appears to be due to the tendency for breaks to accumulate both in the proximal euchromatic portion of each arm and in heterochromatic regions that are not replicated in the polytene chromosomes.

Animals↗
PubMed1977

Estimates of quantal-release and binomial statistical-release parameters at rat neuromuscular junction.

Quantal-release and binomial statistical-release parameters were examined in the isolated rat diaphragm phrenic nerve preparation. The muscle resting potentials were reduced by cutting the muscle fibers to prevent muscle action potentials and contractions. The cutting technique was modified to allow persistent observation of miniature end-plate potentials (MEPPs) and end-plate potentials (EPPs) with intracellular recording techniques. Direct estimates of quantal release were examined and compared with predicted binomial and Poisson distributions. The results indicate that release is binomial when the nerve is stimulated with low- or high-frequency stimuli. The indirect method of estimating quantal release (variance method), which assumes release is described by a Poisson distribution, seriously overestimates quantal release. The binomial analysis indicates that the statistical store is small (less than 90 quanta) and that most of these quanta are released with each nerve impulse.

Animals↗
PubMed1986

The question of the total gene number in Drosophila melanogaster.

A statistical analysis has been carried out on the distribution and allelism of nearly 500 sex-linked, X-ray-induced, cytologically normal and rearranged lethal mutations in Drosophila melanogaster that were obtained by G. Lefevre. The mutations were induced in four different regions of the X chromosome: (1) 1A1-3E8, (2) 6D1-8A5, (3) 9E1-11A7 and (4) 19A1-20F4, which together comprise more than one-third of the entire chromosome.--The analysis shows that the number of alleles found at different loci does not fit a Poisson distribution, even when the proper procedures are taken to accommodate the truncated nature of the data. However, the allele distribution fits a truncated negative binomial distribution quite well, with cytologically normal mutations fitting better than rearrangement mutations. This indicates that genes are not equimutable, as required for the data to fit a Poisson distribution.--Using the negative binomial parameters to estimate the number of genes that did not produce a detectable lethal mutation in our experiment (n0) gave a larger number than that derived from the use of the Poisson parameter. Unfortunately, we cannot estimate the total numbers of nonvital loci, loci with undetectable phenotypes and loci having extremely low mutabilities. In any event, our estimate of the total vital gene number was far short of the total number of bands in the analyzed regions; yet, in several short intervals, we have found more vital genes than bands; in other intervals, fewer. We conclude that the one-band, one-gene hypothesis, in its literal sense, is not true; furthermore, it is difficult to support, even approximately.--The question of the total gene number in Drosophila will, not doubt, eventually be solved by molecular analyses, not by statistical analysis of mutation data or saturation studies.

Alleles↗
PubMed1984

Temporal characteristics of seizures and epileptiform discharges.

The time relations of epileptic events have been studied in 3 sets of data: (I) counts of individual epileptiform discharges in twelve 48 h EEG recordings, (IIa) seizure calendars of 30 therapy-resistant outpatients participating in a drug trial, (IIb) seizure calendars of 10 mentally subnormal epileptic patients resident in a long-stay unit. The EEG data I were characterized most often by a Poisson distribution of intervals between discharges and the occurrence of marked periodicities, particularly at night. The periods of rhythmic nocturnal events ranged from 13 to 142 min and did not appear to correspond to the REM/non-REM cycle. In the seizure data IIa and b a Poisson distribution of intervals between events was found in half the patients. Periodicities occurred only in group IIa and did not correspond to weekly or monthly cycles. A stochastic process is considered to be the model which best fits these data.

Adolescent↗
PubMed1983

Clustering of rare events.

The clustering of cases of a rare disease is considered. The number of events observed for each unit is assumed to have a Poisson distribution, the mean of which depends upon the population size and the cluster membership of that unit. Here a cluster consists of those units that are homogeneous in their rate of occurrence of the rare events under study. A sample of units is modeled by a mixture of Poisson distributions, one for each cluster, the mixing parameters being the proportions of all units represented by the components of the mixture. Maximum likelihood and Bayes approaches are employed to determine criteria for separating a sample into groups of units with homogeneous rates. A likelihood ratio test for the significance of a two-component mixture is presented as an example. The performance of the criteria is illustrated with data on the spatial occurrence of sudden infant deaths (SIDs) in North Carolina counties over a four-year period. The results suggest that the practice of dividing the counties into high- and low-risk categories on the basis of the ordered rates alone should be questioned. Tests based upon combinatorial methods are also presented to examine the significance of the number of contiguous counties among those with high rates.

Biometry↗
PubMed1986

Sensitivity of neurons in the auditory midbrain of the grassfrog to temporal characteristics of sound. I. Stimulation with acoustic clicks.

The coding of fine-temporal structure of sound, especially pulse repetition rate, was investigated on the single-unit level in the auditory midbrain of the grassfrog. As stimuli periodic click trains and Poisson distributed click ensembles have been used. The response to periodic click trains was studied in two aspects, focussing on two types of possible codes: a rate code and a synchrony code. From the iso-intensity rate histogram five basic average response rate characteristics as function of pulse repetition rate have been established: low-pass, band-pass, high-pass, bimodal and non-selective unit types. The synchronization capability, expressed in a synchronization index, was for a small majority of units non-significant and a low-pass function of pulse repetition rate for most of the other units. The rate code showed the largest diversity of response types and an enhanced selectivity to pulse repetition rate. The stimulus-response relation to Poisson distributed click ensembles was investigated by a non-linear system theoretical approach. On the basis of first- and second-order Poisson kernels possible neural mechanisms accounting for temporal selectivity were determined. A considerable fraction of units exhibited response characteristics that were invariant to changes in sound pressure level and average click rate. These units may function as feature detectors of fine-temporal structure of sound. The spectro-temporal sensitivity range of the auditory midbrain of the grassfrog appeared to be broad and not particularly tuned to the ensemble of conspecific cells.

Acoustic Stimulation↗
PubMed2001

The use of mixture models for identifying high risks in disease mapping.

Conventional approaches for estimating risks in disease mapping or mortality studies are based on Poisson inference. Frequently, overdispersion is present and this extra variability is modelled by introducing random effects. In this paper we compare two computationally simple approaches for incorporating random effects: one based on a non-parametric mixture model assuming that the population arises from a discrete mixture of Poisson distributions, and the second using a Poisson-normal mixture model which allows for spatial autocorrelation. The comparison is focused on how well each of these methods identify the regions which have high risks. Such identification is important because policy makers may wish to target regions associated with such extreme risks for financial assistance while epidemiologists may wish to target such regions for further study. The Poisson-normal mixture model is presented from both a frequentist, or empirical Bayes, and a fully Bayesian point of view. We compare results obtained with the parametric and non-parametric models specifically in terms of detecting extreme mortality risks, using infant mortality data of British Columbia, Canada, for the period 1981-1985, breast cancer data from Sardinia, for the period 1983-1987, and Scottish lip cancer data for 1975-1980. However, we also investigate the performance of these models in a simulation study. The key finding is that discrete mixture models seem to be able to locate regions which experience high risks; normal mixture models also work well in this regard, and perform substantially better when spatial autocorrelation is present.

Adult↗
PubMed1986

Cell survival and radiation induced chromosome aberrations. I. Derivation of formulae for the determination of transmission and survival parameters of aberrations.

Existing mathematical formulations to predict the frequency of radiation induced chromosome aberrations in 2nd post-irradiation division are based on the Poisson distribution [3, 4]. Meanwhile several studies have shown that intercellular distributions exist, deviating from Poisson. In the present study a modified model was developed which permits the application of empirical distributions. Transmission and survival parameters of aberrations can be iteratively computed. A general formula was derived for the calculation of cell survival from 1st to 2nd division.

Cell Survival↗
PubMed1995

Quantifying intracellular radioresponse diversity in irradiated sandwich cultures via micronucleus expression.

Determining the degree of diversity in therapeutic sensitivity exhibited by a tumour population is of considerable clinical importance. In addition to being a contributor to radiation resistance, diversity is the basis for variation in sensitivity over the course of treatment. To study intrapopulation diversity in radiosensitivity following gamma-irradiation (2 Gy), distributions of the number of micronuclei/binucleate cell were obtained for human cervix carcinoma sandwich populations. Cell-to-cell diversity in radioresponse (micronucleus expression) was quantified using the overdispersion index ((variance/mean)--1). As measured by this index, the radioresponse diversity of sandwich cultures sharply increased after introduction of oxygen/nutrients to the cultures, mimicking tumour reperfusion. In addition, a strong correlation was found between this measure of diversity and the extent to which the fraction of cells without micronuclei exceeds that expected from a Poisson distribution. This correlation indicates that for a diverse population there can be a significant departure of the aggregate population sensitivity (determined, for instance, by log-survival in a clonogenic assay) from that inferable from simply averaging per-cell sensitivities (reflected, e.g. by mean number of chromosome aberrations/cell). Our experimental results suggest a model attributing diversity in a population to its being a mixture of distinct subpopulations, each biologically homogeneous with respect to micronucleus expression, and each contributing an individual Poisson-distributed micronucleus response. We demonstrate how such radiodiversity may be quantified and show that reoxygenation of a microenvironmentally heterogeneous population leads to an increase in its radiobiological diversity.

Cell Cycle↗