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At least 199 records · Page 11Linked to original sources
PubMed1996

Clustered distribution of calcium sensitivities: an indication of hetero-tetrameric gating components in Ca2+-activated K+ channels reconstituted from avian nasal gland cells.

Calcium-activated potassium channels (maxi K+ channels) isolated from avian nasal salt gland cells were reconstituted into lipid bilayers and characterized. The 266 pS channel is blocked discretely by charybdotoxin from the external solution at nanomolar concentrations and by Ba2+ from the cytosolic side at micromolar concentrations. Fast tetraethylammonium (TEA) block is seen as apparent reductions in amplitude of the unitary currents. From the extent of the reductions, TEA binding affinity was calculated to be 0.16 mM from the external solution and 37 mm from internal solution. The overall channel properties conform to those of maxi K+ channels in other epithelial tissues. The calcium sensitivity of the channel was found to be variable from channel to channel, extending over a wide range of concentrations from 1 to 1,000 microM. Examination of the pooled calcium titration curves, revealed that these curves are grouped into five clusters, and the probability distribution of the clusters matches a binomial distribution. The Hill coefficient derived from the titration curves varies from 1 to 5 and is linearly correlated to calcium binding with a slope of 1 per 10-fold change in Kd. Clustered titration curves with such a characteristic suggest that the gating components and the calcium binding sites of the maxi K+ channels in the avian nasal gland are hetero-tetrameric and may result from random mixing of two distinct subunits possessing high and low calcium sensitivities, respectively.

Animals↗
PubMed1997

Cooperative effects of photodynamic treatment of cells in microcolonies.

Microcolonies of 2-8 Madison-Darby canine kidney cells (MDCK II) and Chinese hamster lung fibroblasts (V79) cells were incubated with the photosensitizer Photofrin and exposed to light, and the resulting number of dead cells per colony was determined. The distribution of this number was found to be incompatible with the assumption that cells are inactivated independently. The experimental distributions were significantly different from the binomial distribution expected from this assumption, but in accordance with a model in which an inactivated cell can inactivate adjacent cells with a certain probability. These findings are contrary to the common view that damage caused by radiation is limited to the cell in which the primary damage takes place. Our findings clearly indicate some kind of cooperativity between cells treated with Photofrin and light.

Animals↗
PubMed1999

Echinococcus granulosus larvae in the livers of sheep in Tunisia: the effects of host age.

A baseline survey of hepatic hydatid disease in sheep in Tunisia was undertaken. Prevalence and intensity (i.e. the number of cysts/liver) were both found to increase with age. The age-specific trends in these two parameters indicate that Echinococcus granulosus is in an endemic equilibrium steady-state in Tunisia and therefore amenable to control. The distribution of parasites within the livers of the hosts followed a negative binomial distribution. The negative binomial constant, k, increased with age, indicating that there was a lower propensity for aggregation of parasites in the hosts as the sheep became older.

Age Factors↗
PubMed2004

A quantitative risk assessment of waterborne cryptosporidiosis in France using second-order Monte Carlo simulation.

A pragmatic quantitative risk assessment (QRA) of the risks of waterborne Cryptosporidium parvum infection and cryptosporidiosis in immunocompetent and immunodeficient French populations is proposed. The model takes into account French specificities such as the French technique for oocyst enumeration performance and tap water consumption. The proportion of infective oocysts is based on literature review and expert knowledge. The probability of infection for a given number of ingested viable oocysts is modeled using the exponential dose-response model applied on published data from experimental infections in immunocompetent human volunteers challenged with the IOWA strain. Second-order Monte Carlo simulations are used to characterize the uncertainty and variability of the risk estimates. Daily risk of infection and illness for the immunocompetent and the immunodeficient populations are estimated according to the number of oocysts observed in a single storage reservoir water sample. As an example, the mean daily risk of infection in the immunocompetent population is estimated to be 1.08 x 10(-4) (95% confidence interval: [0.20 x 10(-4); 6.83 x 10(-4)]) when five oocysts are observed in a 100 L storage reservoir water sample. Annual risks of infection and disease are estimated from a set of oocyst enumeration results from distributed water samples, assuming a negative binomial distribution of day-to-day contamination variation. The model and various assumptions used in the model are fully explained and discussed. While caveats of this model are well recognized, this pragmatic QRA could represent a useful tool for the French Food Safety Agency (AFSSA) to define recommendations in case of water resource contamination by C. parvum whose infectivity is comparable to the IOWA strain.

Animals↗
PubMed1983

Studies on the low and fundamental populations of the warble fly Hypoderma bovis (De Geer) (Diptera, Hypodermatidae).

During control measures against cattle hypodermatosis low populations of warble flies with incidence of infestation (extensity, percentage) up to 2-5% persist after a rapid decrease of the degree of infestation. In order to study these low populations isolated warble fly populations were experimentally created under conditions of Central Europe. Fundamental populations observed originated from one ovipositing female in a herd of heifers and included 17, 25, 42 and 83 larvae with 11-52% of infestation and mean infestation of 1.1-1.6 larvae per infested host (intensity of infestation). With the increasing age of heifers from one to 2.5 years the numbers of fundamental populations decreased to one quarter, the extensity of infestation to one fifth, while the mean infestation per infested host remained nearly at the same level. The persistence of low warble fly populations was caused by an internal system regulating the numbers of parasites in the host populations. The distribution of larvae of fundamental warble fly population in a cattle herd agrees with the Poisson distribution as well as the negative binomial distribution. The direct significance of the results obtained for the control of hypodermatosis is pointed out.

Animals↗
PubMedDate not supplied

A random graph model for the final-size distribution of household infections.

In epidemiological/disease control studies, one might be interested in estimating the parameters community probability infection (CPI) and the household secondary attack rate (SAR), as introduced by Longini and Koopman. The quasi-binomial distribution I (QBD I) with parameters n, p and theta, introduced by Consul, is proposed as a model for the final-size distribution of household infections, where p (CPI) is the probability of an individual being infected from the community and theta (SAR) is the rate of secondary transmission of infection within household. An individual can be infected either from within the household or from the community. Let X be the total number of infected members in a household of size n. Then the distribution of X is given by the QBD I with the probability mass function: (formula: see text) with 0 < p < 1, theta > or = 0 such that p + n theta < 1. The epidemic model is derived from a directed random graph. Data from influenza epidemics in Asian and American households are used to test the model and a comparison is made with the Longini-Koopman model. It is shown empirically that the QBD I is as good as the L-K model in describing the household infectious disease data, and both models provide almost identical estimates for community and household transmission parameters although they are derived from different perspectives and conditions.

Asia↗
PubMed2002

Host manipulation by Ligula intestinalis: a cause or consequence of parasite aggregation?

Previous investigations suggest that the infection of the cyprinid roach, Rutilus rutilus, with the larval plerocercoid forms of the cestode, Ligula intestinalis, creates behavioural and morphological changes in the fish host, potentially of adaptive significance to the parasite in promoting transmission to definitive avian hosts. Here we consider whether these behavioural changes are important in shaping the distribution of parasite individuals across the fish population. An examination of field data illustrates that fish infected with a single parasite were more scarce than expected under the negative binomial distribution, and in many months were more scarce than burdens of two, three or more, leading to a bimodal distribution of worm counts (peaks at 0 and >1). This scarcity of single-larval worm infections could be accounted for a priori by a predominance of multiple infection. However, experimental infections of roach gave no evidence for the establishment of multiple worms, even when the host was challenged with multiple intermediate crustacean hosts, each multiply infected. A second hypothesis assumes that host manipulation following an initial single infection leads to an increased probability of subsequent infection (thus creating a contagious distribution). If manipulated fish are more likely to encounter infected first-intermediate hosts (through microhabitat change, increased ingestion, or both), then host manipulation could act as a powerful cause of aggregation. A number of scenarios based on contagious distribution models of aggregation are explored, contrasted with alternative compound Poisson models, and compared with the empirical data on L. intestinalis aggregation in their roach intermediate hosts. Our results indicate that parasite-induced host manipulation in this system can function simultaneously as both a consequence and a cause of parasite aggregation. This mutual interaction between host manipulation and parasite aggregation points to a set of ecological interactions that are easily missed in most experimental studies of either phenomenon.

Animals↗
PubMed1990

The relationship between the frequency distribution of Ascaris lumbricoides and the prevalence and intensity of infection in human communities.

Observed field data from a range of geographically distinct human communities suggest a consistent non-linear relationship between prevalence and mean intensity of Ascaris lumbricoides infection. Utilizing the negative binomial distribution as a description of observed aggregation, maximum-likelihood analysis reveals that the degree of aggregation is a negative linear function of mean worm burden. The factors responsible for this relationship in human populations require further study but may involve some combination of (i) density-dependent reduction in worm numbers within individuals, (ii) density-dependent parasite-induced host mortality or (iii) self-treatment by heavily infected hosts. Variability in the degree of aggregation appears dependent on the level of infection in a community and independent of geographical differences in the host or parasite populations.

Animals↗
PubMed2006

Typicality Index of the Strong Interest Inventory: a binomial analysis.

The Typicality Index of the 2004 Strong Interest Inventory was developed by Donnay, Morris, Schaubhut, and Thompson to identify inconsistent or other atypical responding. Analysis by the binomial distribution shows that the index, with the recommended cut score, correctly classifies 95.1% of randomly completed inventories.

Binomial Distribution↗
PubMed1993

Distribution of the number of Eurytrema sp. eggs per gram of feces in naturally infected cattle.

Eurytrema sp. egg counts (epg) in the feces of naturally infected cattle were performed and the technique employed showed 94.2% probability of detecting positive cases of the infection with a single examination independently of the host parasite burden. It was also demonstrated that the epg of Eurytrema sp. follows a negative binomial distribution model and is characterized by its small magnitude.

Animals↗
PubMed2000

Stochastic host-parasite interaction models.

We contribute to the discussion of causes and effects of aggregation (overdispersion) of macroparasite counts, focussing particularly upon the effects of clumped infections and parasite-induced host mortality. The simple nonlinear stochastic model for the evolution of the parasite load of a single host, investigated in Isham (1995), is extended to allow three parasite stages (larval, mature and offspring), and to allow durations of these stages to be non-exponentially distributed. As in the earlier work, exact algebraic results are possible, providing insight into the aggregation mechanisms, as long as the only source of interaction between host and parasites is an excess host mortality linearly related to the parasite load. Results are obtained on the distribution of parasite load and on host survival. In particular, although parasite-induced host mortality is usually thought of as a process that reduces parasite aggregation (Anderson and Gordon 1982), it is shown that, for this model, parasite-induced host mortality cannot cause the index of dispersion to fall below unity. Host heterogeneity and disease control are also discussed. An approximation based on moment assumptions appropriate to a specially-constructed multivariate negative binomial distribution is proposed. This approximation, which is applicable to other processes, and an alternative based on the multivariate normal distribution are compared with exact results.

Animals↗
PubMed1997

Sex ratio in relation to fathers' occupations.

OBJECTIVE: To investigate whether the sex ratio of children varies between fathers of different occupations. METHODS: The sex ratio (the ratio of the number of boys to the number of girls at birth) was calculated in relation to paternal occupation in the cohort of all 253,433 live births in Cumbria, north west England, from 1950-89. Exact binomial confidence intervals were used to estimate whether the sex ratio in each occupational category was significantly different from that for the rest of the cohort. RESULTS: There were fewer occupational categories with significantly different sex ratios at the 5% level than expected by chance alone, assuming the same binomial distribution of sexes at birth within each paternal occupation. CONCLUSIONS: Significant variation of the sex ratio with fathers' occupations was not found. There is some evidence that the sex ratio shows less variance than expected under a binomial model which assumes independence of the sex of each child; a possible explanation of this may be parental preference for limiting family size after children of both sexes have been born or some other factor which results in children within a family being more likely to be of both sexes rather than the same sex.

Binomial Distribution↗
PubMed1993

An evaluation of some methods for fitting dose-response models to quantal-response developmental toxicology data.

The analysis of quantal-response developmental toxicology data by dose-response modeling is discussed, with emphasis on methods that avoid exact distributional assumptions. These methods (quasi-likelihood, bootstrapping, and jackknifing) are contrasted with analyses based on the beta-binomial distribution. For the resampling procedures, dose-response models are fit under a binomial likelihood. A justification for this choice of estimator in resampling plans is given, based on an extension of the standard results for asymptotic normality and consistency of maximum likelihood estimators. This justification depends only on the true distribution of the data having the usual binomial expectation. A quasi-likelihood approach is also considered, in which simple assumptions about the intralitter correlation structure are made. Quasi-likelihood methods are in theory asymptotically robust to misspecification of the intralitter correlation structure. The practical implications of these asymptotic results are evaluated in a simulation study.

Abnormalities, Drug-Induced↗
PubMed1995

Multiple comparisons procedures for comparing several treatments with a control based on binary data.

In this paper, we examine three approaches for comparing several treatments with a control with use of binary response data. The first approach relies on asymptotic theory applied to the Freeman-Tukey transformation of the observed proportions. The second finds an acceptance region based on the binomial distributions estimated under the joint null hypotheses. The third approach applies Dunnett's procedure to the binary data. We evaluated the actual overall type I error rates of the Freeman-Tukey test and Dunnett's procedure using both simulation and binomial calculations while we assessed those of the binomial approach using simulation. Based upon their capability to preserve the desirable overall type I error rate, we provide recommendations regarding the choices among the three approaches for various occasions. In addition, we provide comments on the power of these three approaches.

Binomial Distribution↗
PubMed2004

Samples of exact k-stage group sequential designs for Phase II and Pilot studies.

That the test of H(0): p=p(0) versus H(1): p>p(0) can be based on a binomially distributed random variable is widely known among users of statistical methods. What is not generally known is that under certain very general conditions, it is possible to find an exact k-stage group sequential test whose total sample size is bounded above by the sample size for the single stage binomial test. That is, it is possible to find k-stage tests for detecting H(1) for which the sum of the sample sizes at each of the stages is bounded above by the sample size for the standard binomial test. This result is somewhat remarkable since the total sample size under the group sequential test setting can be strictly less than the sample size for the uniformly most powerful (UMP) one-stage binomial test. In other words, exact group sequential tests cannot only save the average sample size but can also save the maximum sample size when they are compared to the standard binomial test. In this paper, implications of existing theory are explored and a web application written by the authors is presented. No new theory is established. Applications are described and methods are demonstrated that use the web application to rapidly create efficient designs for Phase II and Pilot studies that put a minimum number of patients at risk and that facilitate the rapid progression through a scientific research agenda. While couched here in the context of clinical trials, the results may be used in any field of inquiry where inferences are made based on the size of a binomial random variable.

Binomial Distribution↗
PubMed1988

Quantitative genetic analysis of bi-iliac breadth.

Bi-iliac breadth, the frontal maximum diameter between right and left iliac crests, was measured in 1,547 male and 2,085 female residents of a rural area in Japan. All subjects were over 14 years of age. The bi-iliac breadth showed an increase related to age but little sex difference. Modification of age and sex variations from the measured value was obtained by calculation of the score, represented by arithmetical means and standard deviations. Distribution of these scores appeared to be binomial, and since binomial distribution approaches normal distribution when n is large, it is presumed that this trait gains normal distribution. Thus variation of bi-iliac breadth in subjects 20-79 years of age enables us to analyze inheritance. No significant difference was found between husband and wife in the correlation coefficients or between father and daughter (0.13 +/- 0.08). Significant differences were found as follows: father-son (0.35 +/- 0.05) (P less than 0.001), mother-son (0.28 +/- 0.05) (P less than 0.001), and mother-daughter (0.28 +/- 0.06) (P less than 0.001). There was no indication of maternal or paternal effects, since no significant difference was found in father-child and mother-child correlation coefficients. It is concluded that bi-iliac breadth is a quantitative genetic trait under control of polygenes on autosomes. Regression coefficient of child on midparental value was 0.55 +/- 0.05, approximately twice the means of four pairs of correlation coefficients between parent-offspring. Narrowly, heritability was estimated as 0.54 approximately 0.55. Contribution of dominance to total variance was small (VD = 0.11), in contrast to the larger additive genetic variance (VA = 0.54).

Adolescent↗
PubMed1983

Patterns of fusimotor innervation by gamma-efferents in cat peroneus tertius.

The pattern of gamma-efferent innervation of the muscle spindle was investigated in the peroneus tertius muscle of the cat. A number of spindle group Ia afferents were isolated and monitored during tetanic stimulation of isolated gamma-axons. The sample was dominated by efferents producing a static fusimotor effect on the afferent. An individual static axon normally projected to less than five but at times as many as seven muscle spindles. Each spindle normally received innervation from three to five static gamma-efferents but occasionally up to eight. The number of spindles innervated by a static gamma-axon was directly related to the efferent axonal conduction velocity. For each experiment, a probability distribution of the number of fusimotor effects was constructed from all available connections between the muscle spindles and static gamma-efferents considered in matrices of four afferents and four efferents. This distribution was then compared to a random binomial distribution. In each of the ten experiments, statistically significant differences (p less than 0.01) were noted between the experimental and random distributions. In order to interpret such deviations from the random distributions, similar analyses were performed on various combinations of afferents and efferents in simulated sets displaying grouping of effects. It was concluded that the observed differences between experimental and random distributions may be produced by a grouping of fusimotor innervation limited to a small set of spindles.

Afferent Pathways↗
PubMed1976

Evoked neurotransmitter release: statistical effects of nonuniformity and nonstationarity.

Recent studies of the mechanism of quantal neurotransmitter release have assumed that the number of quanta released at each stimulation is binomially distributed and have sought to estimate the binomial parameters n and p. Mathematical analysis and computer simulations show that temporal variation in the number of eligible or filled release sites and either spatial or temporal variation in the probability of release at a site can drastically bias such estimates, while the experimental histograms remain statistically indistinguishable from those predicted by the binomial law. Interpretation of the estimates n and p in terms of ultrastructural or physiological characteristics of the nerve terminal is liable to significant error if departures from the binomial assumptions are not suitably assessed.

Computers↗