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PubMed1985

Characterization of a cation channel on the apical surface of the frog lens epithelium.

The properties of a single conductance pathway of the apical (fibre-facing) surface of the frog lens epithelium are reported. Using the patch-clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981), the most common single-channel currents had an amplitude of 1.9 pA, the mean open time 2.1 ms and a conductance of 25 pS. One open-state time constant (to = 3.3 ms) and two closed-state time constants (tau c1 = 0.9 ms, tau c2 = 23.1 ms) were resolved. The channel current and the mean open time were both increased when Ca2+ was removed from the external solution and the open time distribution was no longer fitted by a single exponential. Multiple-channel events in cell-attached patches containing two or more identical channels were distributed in a binomial fashion and the probability that an individual channel was open, obtained by fitting the binomial distribution, was 0.039. The channel was found to have a Na+:K+ selectivity ratio of 3:1. When Ca2+ was removed from the pipette solution the probability that an individual channel was open increased to 0.137 and the Na+:K+ selectivity ratio increased to 4:1. Channel activity was observed in the presence of tetrodotoxin (10(-6) M) in the bathing medium and the pipette solution but was abolished by internal perfusion of the patch pipette with 0.5 x 10(-4) M amiloride. this apical conductance pathway is identified as an amiloride-sensitive cation channel. These channels are clustered in groups on the apical membrane, spontaneously active at the resting potential and with the possibility of altering their Na+:K+ selectivity. They represent a distinct type of channel, that differ from nerve and muscle Na+ channels in their manner of activation, but do share some common features with both Na+ and Ca2+ channels in excitable cells.

Amiloride↗
PubMed2000

B chromosomes in two fish species, genus Rhamdia (Siluriformes, Pimelodidae).

Specimens belonging to two fish species genus Rhamdia were cytogenetically analysed from seven localities in Brazil and Argentina. In addition to the 58 chromosomes of the basic karyotype, one to five metacentric B chromosomes were observed carrying conspicuous heterochromatic blocks on the distal regions of both chromosome arms. These B chromosomes are mitotically stable and, in the two best-sampled populations in R. hilarii (Lobo and 29 reservoirs), they showed frequency distributions fitting a binomial distribution, though Bs were more frequent in the latter. The presence of B chromosomes with the same appearance in R. quelen suggests an ancient origin for these B chromosomes, presumably prior to speciation from a common ancestor.

Animals↗
PubMed1989

[Natural microbial control of crickets populations (Orthoptera: Gryllotalpidae: Scapteriscus borellii): regulation of populations aggregated in time and space].

From 1983 through 1988, a total of 1,762 collections, containing 31,312 individuals of the mole cricket, Scapteriscus borellii, were made, principally in the State of São Paulo, Brazil. Collections were found to fit a negative binomial distribution both as whole and when divided into monthly collections. In these collections, an iridovirus, a entomogenous nematode, and the fungi Metarhizium anisopliae, Beauveria bassiana, Paecilomyces sp., and Entomophtora sp., were found to be agents of natural mortality, although usually as endozootics and relatively rarely as epizootics and panzootics. As a group, these diseases were also distributed in a binomial negative. These data suggest that the temporal and spatial aggregations of the mole crickets, produced by high rates of migration among suitable habitats, are adaptations to outbreaks of epidemics, which also serve as mole cricket population regulators. These ideas are develop and derived from simple mathematical models of population change.

Animals↗
PubMed1979

Predictive probability early termination plans for phase II clinical trials.

A phase II clinical trial is designed to gather data to help decide whether an experimental treatment has sufficient effectiveness to justify further study. In a one-arm trial with dichotomous outcome, we wish to test a simple null hypothesis on the Bernoulli parameter against a one-sided alternative in a sample of N patients. It is advisable to have a rule to terminate the trial early when evidence accumulates that the treatment is ineffective. Predictive probabilities based on the binomial distribution and beta and uniform prior distributions for the binomial parameter are found to be useful as the basis of group sequential designs. Size, power and average sample size for these designs are discussed. A process for the specification of an early termination plan, advice on the quantification of prior beliefs, and illustrative examples are included.

Antineoplastic Agents↗
PubMedDate not supplied

[The determination of the upper limits of year-round morbidity].

The use of K. Pearson's criterion has made it possible to establish that the empirical rows presenting the annual data on dysentery morbidity for each month during the period of many years correspond to binomial distribution. For this reason, the calculation of the highest limit of annual morbidity for many years should be made with the use of the formulae of great radices of quadratic inequation [formula: see text] used in mathematical statistics for the determination of the highest limits in binomial distribution. For the number of observations (n) not the number of inhabitants (which contradicts to the notion of observation in the theory of probability), but the number of minimal values of monthly morbidity, used for the calculation of the minimal average morbidity value omega or theta*, should be taken. To obtain objective results, the minimal average value omega or theta* and the ratio t2/2n must be of the same order, where t is the critical value of Student's criterion equal to 1.96.

Bacterial Infections↗
PubMed1997

The latent class model for multiple binary screening tests.

Given multiple binary tests, such as repeated application of a blind screening test to each individual in a sample, we attempt to estimate the prevalence, sensitivity and specificity of the test without knowing the true disease status of those tested (gold standard). This problem is equivalent to finding the mixing distribution of a mixture of binomial distributions. We suggest a new method to determine the number of latent classes. Our simulations show that the coverage probabilities of the bootstrap confidence intervals of our estimates are correct. Our methods are illustrated by examples from published medical research.

Algorithms↗
PubMed2005

Detection of anthelmintic resistance: a comparison of mathematical techniques.

Anthelmintic resistance has become an increasing problem particularly to gastrointestinal tract nematodes and appropriate methods are required to detect this phenomenon so the correct action can be taken. This paper compares a number of mathematical techniques that are used to analyse data. The negative binomial distribution is a mathematical distribution used to model aggregated data and hence is suitable to model the intensity of parasite burden and the magnitude of the faecal egg counts. Maximum likelihood techniques are utilised to exploit this mathematical distribution to analyse the magnitude of the faecal egg count reduction and decline in the worm burden in response to anthelmintic treatment. Data from experimental groups of sheep described in the accompanying paper are used. In addition, simulated data sets of faecal egg counts were created using a random number generator following appropriate negative binomial distributions. The results demonstrate this statistical model can detect evidence of anthelmintic resistance with a faecal egg reduction test that otherwise might require a slaughter trial to demonstrate. In addition, the simulated data sets confirm that there is a significant probability of failure to detect low anthelmintic efficacy with commonly used mathematical techniques. Consequently, the use of maximum likelihood mathematical techniques with a negative binomial statistical model would aid in the early detection of anthelmintic resistance using faecal egg count reductions and result in a lower probability of inappropriately assigning an anthelmintic as effective.

Animals↗
PubMed1998

The subclass approach for mutational spectrum analysis: application of the SEM algorithm.

Analysis and comparison of mutational spectra represents an important problem in molecular biology. To analyse a mutational spectra we apply an algorithm based on the SEM subclass approach (Simulation, Expectation, Maximization). The algorithm tries to classify the mutational sites according to different mutation probabilities, and each site should belong to one class. Each class is approximated by binomial distribution and thus any real mutational spectrum is regarded as a mixture of binomial distributions. The separation process runs iteratively. Each iteration includes the simulation, maximization and estimation procedures. To evaluate the quality of the classification results, the X2 test is used. The algorithm has been checked on random spectra with preset parameters and on real mutational spectra. As has been shown, 17 out of 19 analysed real mutational spectra can be divided into two or more classes of sites, of which one contains hotspots of mutation. For the G:C-->A:T mutational spectra induced by Sn1 alkylating mutagenes (11 spectra) the classification accuracy was 0.95. To test different site volumes, each Sn1-induced spectrum was divided into the G-->A and C-->T spectra. The classification accuracy for these spectra was 0.96. From the analysis of classification errors it is possible to suggest that at least part of them cannot be ascribed to the faults of the algorithm but are caused by some special features of the mutagenesis itself. The results of the real data are in good relation with existing knowledge. The approach we present is an attempt to formalize the concept of a "mutational hotspot". The program implementing the SEM algorithm is available on the Web server (http:/(/)www.itba.mi.cnr.it/webmutation).

Algorithms↗
PubMed2006

Statistical description of sediment transport experiments.

A longstanding problem in the study of sediment transport in gravel-bed rivers is related to the physical mechanisms governing bed resistance and particle motion. To study this problem, we investigated the motion of coarse spherical glass beads entrained by a steady shallow turbulent water flow down a steep two-dimensional channel with a mobile bed. This experimental facility is the simplest representation of sediment transport on the laboratory scale, with the tremendous advantages that boundary conditions are perfectly controlled and a wealth of information can be obtained using imaging techniques. Flows were filmed from the side by a high-speed camera. Using image processing software made it possible to determine the flow characteristics such as particle trajectories, their state of motion (rest, rolling, or saltating motion), and flow depth. In accordance with earlier investigations, we observed that over short time periods, sediment transport appeared as a very intermittent process. To interpret these results, we revisited Einstein's theory on sediment and derived the statistical properties (probability distribution and autocorrelation function) of the key variables such as the solid discharge and the number of moving particles. Analyzing the autocorrelation functions and the probability distributions of our measurements revealed the existence of long-range correlations. For instance, whereas theory predicts a Binomial distribution for the number of moving particles, experiments demonstrated that a negative binomial distribution best fit our data, which emphasized the crucial role played by wide fluctuations. These frequent wide fluctuations stemmed particle entrainment and motion being collective phenomena rather than individual processes, contrary to what is assumed in most theoretical models.

Journal Article↗
PubMedDate not supplied

[Lernaea cyprinacea (Copepoda, Lernaeidae) from crucian carp Carassius carassius from the Dlinnoje Lake in the middle stream of the Vychegda River].

Till 1996 the Vychegda River's flood lakes at the territory of the biological station of the Syktyvkar University were overflowed every spring by water so that fishing took place from time to time. In 1996 a low flood level and intensive fishing resulted in the change of the infection rate of crucians by Lernaea, as well as in the change of the size and sex ratios of the crucian population in the Dlinnoje Lake. Thus, the size pattern of the crucian population became simpler, and it led to the changes in parasite-host relation. As a result, the intensity of the invasion of crucians by Lernaea cyprinacea have increased and the distribution of the parasite in the host population does not fit by the negative-binomial distribution. Crucian females and males play an equal role in the maintenance of the parasite population. In 1984 crucian females of medium and large body length played the main role in that process. Functions of other host groups (fishes of small body length, males) were different. Up to 2001 a significance of "k"-exponent of the negative-binomial distribution, describing the number of copepods in the mature part of crucian population, changed with a small range that suggests a stability of parasite-host relationship in the investigated crucian groups. We suppose that after a period of an unstable state in 1997-2000 the population of the parasite reached a new stable state.

Animals↗
PubMed2006

Within-plant distribution and binomial sampling of Pentalonia nigronervosa (Hemiptera: Aphididae) on banana.

The banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), infests banana (Musa spp.) worldwide. Pentalonia nigronervosa is the vector of Banana bunchy top virus (family Nanoviridae, genus Babuvirus) the etiological agent of Banana bunchy top disease (BBTD). BBTD is currently the most serious problem affecting banana in Hawaii. Despite the importance of this vector species, little is known about its biology or ecology. There are also no sampling plans available for P. nigronervosa. We conducted field surveys to develop a sampling plan for this pest. Ten plots were surveyed on seven commercial banana farms on the island of Oahu, HI, for the presence of P. nigronervosa on banana plantlets. We found aphids more frequently near the base of plants, followed by the newest unfurled leaf at the top of the plant. Aphids were least likely to be located on leaves in between the top and bottom of the plant. Aphid infestation on surveyed plots ranged from 8 to 95%. We developed a sequential binomial sampling plan based on our surveys. We also discovered that the within-plant distribution of P. nigronervosa is an important factor to consider when sampling for this pest. Our sampling plan will assist in the development of sustainable management practices for banana production.

Animals↗
PubMed1976

On the regularities of distribution of Hypoderma bovis De Geer larvae parasitizing cattle herds in different parts of the range of this warble fly.

The type and parameters of the distribution of the second and third instar larvae of Hypoderma bovis in cattle herds in Czechoslovakia (54 herds, 7233 head), Mongolia (20 herds, 1809 head) and the USSR (48 herds, 4978 head) were studied. A statistical analysis showed a) that in the majority of cases negative binomial distribution serves as a model of the distribution of larvae with sufficient reliability; b) that the regularity of dependence of the distribution exponent k of the negative binomial distribution on the incidence of infestation remains constant in different parts of the range of this warble fly. The latter fact indicates that the regulatory systems limiting the population numbers of this warble fly are associated with host-parasite relationships and do not depend on a complex of conditions specific for various natural zones. In order to understand the regulatory processes in parasite populations it is necessary to study equally the regulatory mechanisms operating primarily on the level of specimens as well as the regulatory systems operating on the level of populations.

Animals↗
PubMed1976

On the regularities of distribution of Hypoderma bovis De Geer larvae parasitizine cattle herds in different parts of the range of this warble fly.

The type and parameters of the distribution of the second and third instar larvae of Hypoderma bovis in cattle herds in Czechoslovakia (54 herds, 7233 head), Mongolia (20 herds, 1809 head) and the USSR (48 herds, 4978 head) were studied. A statistical analysis showed a) that in the majority of cases negative binomial distribution serves as a model of the distribution of larvae with sufficient reliability; b) that the regularity of dependence of the distribution exponent k of the negative binomial distribution on the incidence of infestation remains constant in different parts of the range of thes warble fly. The latter fact indicates that the regulatory systems limiting the population numbers of this warble fly are associated with host-parasite relationships and do not depend on a complex of conditions specific for various natural zones. In order to understand the regulatory processes in parasite populations it is necessary to study equally the regulatory mechanisms operating primarily on the level of specimens as well as the regulatory systems operating on the level of populations.

Animals↗
PubMed1988

Doxapram dosage regimen in apnea of prematurity based on pharmacokinetic data.

To 18 premature apneic patients refractory to theophylline, doxapram (0.5-2.5 mg/kg/h) was administered in combination with therapeutic doses of theophylline. Doxapram concentrations in serum were measured 48 h after commencement of the infusion and then in 2-hour intervals during a 6-8 h withdrawal. Total body clearance (dose/Css) of the drug ranged from 0.20 to 0.56 liter/h in 13 patients and 1.14 to 1.75 liter/h in 4 patients suggesting a binomial distribution in the disposition kinetics of the drug. Other pharmacokinetic indices, although variable, did not exhibit binomial distribution. The mean volume of distribution and half-life of doxapram were 7.33 +/- 4.55 liter/kg and 8.17 +/- 4.13 h, respectively. Based on our calculations to accelerate the attainment of a steady-state plasma concentration (Css) of approximately 1.5 mg/l, a loading dose of 5.5 mg/kg and a maintenance dose of 1 mg/kg/h along with serum concentration monitoring are recommended.

Apnea↗
PubMedDate not supplied

Natural fertility in northeastern Mexico.

BACKGROUND: The aims of this study were as follows: 1) to describe the fertility of a sample of Mexican women (> or =45 years of age, married, not using any family planning methods, and residing in the Mexican state of Nuevo León); 2) to determine whether or not the distribution of completed family size fits the negative binomial distribution, as in other populations studied in the world, and 3) to assess the association between fertility and 10 explanatory variables. METHODS: A sample of 410 women was interviewed at and selected from seven medical units of the Instituto Mexicano del Seguro Social (IMSS). The women were grouped by their year of birth (1896-1925 and 1926-1955) and birthplace [persons whose four grandparents were born in northeastern Mexico (NE) and outside northeastern Mexico (Not-NE)]. A binomial negative distribution analysis was assessed. Multiple linear regression was used to assess association between fertility (transformed by the use of inverse hyperbolic sines) and 10 explanatory variables, including age at marriage, heterozygosity, individual admixture, wife's education, husband's education, wife's occupation, husband's occupation, and couple's residence zone, birth year, and birthplace. RESULTS: Completed fertility was only associated with age at marriage. This population showed a fertility pattern similar to those described in Venezuelan and Brazilian populations in 1950 and 1940, respectively. CONCLUSIONS: We conclude that before worldwide family planning programs, fertility was determined mainly by natural selection forces.

Adolescent↗
PubMed1986

Estimation and analysis of the concentration-response surfaces associated with multiple-agent combinations.

Chinese hamster cells (V79) were treated with ethylnitrosourea (ENU) and cis-diamminedichloroplatinum(II) (DDP) alone and in combination. Sister chromatid exchanges (SCEs) were quantified as measures of genotoxicity of the two agents. The combination experiment employed a factorial design in which cells were treated, in various concentration combinations, with both agents simultaneously. Response surface methodology, using a polynomial model based on a negative binomial distribution of SCE events, was employed for analysis of the interactions of the two genotoxic agents. The negative binomial distribution, a generalization of the Poisson distribution, is required since SCEs are discrete variables which, under the conditions of these experiments, have a distribution which exhibits extra-Poisson variability. The model of the ENU/DDP combinations indicated an increasingly less-than-additive effect resulting from increasing concentrations of each agent in the combination. The analysis of these experiments demonstrates the usefulness of a powerful statistical procedure for evaluating the biological effects resulting from exposure to multiple cytotoxic agents. The methodology can be used with many other types of endpoints and is not limited by the number of treatment agents.

Cells, Cultured↗
PubMed2001

Analysis of the distribution pattern of sister chromatid exchanges in mitotic chromosomes of human T-lymphocytes.

Band locations of 344 sister chromatid exchanges (SCE), observed in chromosome preparations of peripheral T-lymphocyte cultures, were identified using a sequential Q-banding-sister chromatid differentiation staining protocol. A comparison between expected Poisson, expected negative binomial distributions and observed SCE patterns, revealed that the negative binomial distribution provided a better fit to our SCE data. The aggregated pattern of SCE distribution indicated that some bands were more prone to undergo these events. Genetic markers assigned to those bands recording a significant number of exchanges seemed to correspond with the transcriptionally active genes. The results confirm that SCE are induced at the early S-phase of the cell cycle involving the early replicating genes in these events. Potential applications of cytogenetic techniques employed in the present study are proposed.

Chromosome Banding↗
PubMed1976

The distribution of fetal death in control mice and its implications on statistical tests for dominant lethal effects.

In dominant lethal testing fetal death is generally assumed to follow either a Poisson or binomial distribution. However, both of these models were found to be inappropriate when three large sets of mouse control data and other data sets from the literature were examined. The validity of statistical test procedures based on these inappropriate models was then studied in detail. It was found that chi-square tests (which assume an underlying binomial distribution) may seriously exaggerate the level of significance and hence should not be used. In contrast, the inappropriateness of the underlying Poisson or binomial model appeared to have little effect on the validity of pairwise comparisons by analysis of variance procedures. Unlike chi-square, these procedures regard the pregnant female rather than the individual implant as the experimental unit. However, a statistical analysis of dominant lethal data generally involves more than a series of pairwise comparisons, and it is unclear how an invalid underlying model may affect statistical test procedures in this more complex situation. Moreover, it is difficult to justify the use of statistical models that are demonstrably invalid when a reasonable alternative exists. Thus, until a satisfactory parametric model can be found and appropriate test procedures derived, we prefer to analyze dominant lethal data by non-parametric (distribution-free) methods. Proportion of dead implants per female appears to be a more meaningful measure of fetal death than number of dead implants per female for several seasons which include (1) analyses based on proportions take the total number of implants per female into account and (2) analyses based on proportions make more reasonable assumptions concerning pre-implantation losses and are more powerful when such losses occur. Despite our concern with the appropriateness of the underlying model, in practice we have found few instances in which non-parametric and analysis of variance procedures have led to markedly different conclusions.

Animals↗