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PubMed1998

The relationship between microfilarial load in the human host and uptake and development of Wuchereria bancrofti microfilariae by Culex quinquefasciatus: a study under natural conditions.

The uptake of Wuchereria bancrofti microfilariae (Mf) by Culex quinquefasciatus and their development in relation to human Mf density were quantified by allowing a total of 1096 wild mosquitoes to feed on 13 volunteers sleeping under partially open bed-nets. For each volunteer, each hour between 18.00 and 06.00 h the Mf density in finger-prick blood was determined and engorged mosquitoes collected. Each hourly collection of mosquitoes was kept separately. Half of them was dissected within 18 h post-feeding for the presence of ingested Mf, the other half was reared for 12 days to allow for the development of L3 larvae. About 20% of the latter mosquitoes died during these 12 days and these harboured significantly more larvae than the surviving ones, which could be an indication of excess-mortality among heavily infected mosquitoes. Assuming that variability in Mf uptake and in the number of developed L3 larvae can be described by a negative binomial distribution, a maximum-likelihood procedure was applied to estimate the relationship between human Mf density and both the arithmetic mean Mf uptake and L3 development. Both were adequately described by a saturating hyperbolic function that significantly differed from linearity. The saturation level for Mf was estimated at 29 (CI: 20-54) and for L3 larvae at 6.6 (CI: 4.3-17.0). Next, the L3 yield was related to Mf uptake indicating that the W. bancrofti-C. quinquefasciatus complex shows 'limitation', i.e. a decreasing yield for an increasing uptake. Both the number of Mf ingested and the number of L3 larvae developing per mosquito were found to be highly aggregated, with the level of aggregation decreasing in a non-linear way with human Mf density.

Adolescent↗
PubMed2003

[Factors related to sickness absenteeism among nursing personnel].

OBJECTIVE: To analyze short-term leaves among the healthcare staff of a university hospital. METHODS: Study population included 965 nursing professionals active on 1 January 2000. Leaves up to 30 days in one year were analyzed. Sickness leaves (one-year aggregate), service demand, and diagnoses were described. Relative risk was estimated through multivariate analysis, using negative binomial distribution. RESULTS: About 65% of workers generated 1,988 appointments, of which 68.6% lead to absence from work. The greatest demand occurred among nursing technicians, women, and statutory workers (OR=1.61; 1.47; 1.53 respectively). Over half the studied population (57.6%) had at least one absence. This corresponds to 87.8% of workers who had physician appointments. These workers generated a total 1,364 leaves of absence--1.41 per worker--and 5,279 workdays were missed. Multivariate analysis was carried out considering each gender separately. An effect was found only for work regime (RR=1.45 e RR=2.43) for both men and women. CONCLUSIONS: A relationship exists between absenteeism and work regime. It is necessary to include other variables, such as time working for the company, shift, and number of children.

Absenteeism↗
PubMed1995

Efficient pooling designs for library screening.

We describe efficient methods for screening clone libraries, based on pooling schemes that we call "random k-sets designs." In these designs, the pools in which any clone occurs are equally likely to be any possible selection of k from the v pools. The values of k and v can be chosen to optimize desirable properties. Random k-sets designs have substantial advantages over alternative pooling schemes: they are efficient, flexible, and easy to specify, require fewer pools, and have error-correcting and error-detecting capabilities. In addition, screening can often be achieved in only one pass, thus facilitating automation. For design comparison, we assume a binomial distribution for the number of "positive" clones, with parameters n, the number of clones, and c, the coverage. We propose the expected number of resolved positive clones--clones that are definitely positive based upon the pool assays--as a criterion for the efficiency of a pooling design. We determine the value of k that is optimal, with respect to this criterion, as a function of v, n, and c. We also describe superior k-sets designs called k-sets packing designs. As an illustration, we discuss a robotically implemented design for a 2.5-fold-coverage, human chromosome 16 YAC library of n = 1298 clones. We also estimate the probability that each clone is positive, given the pool-assay data and a model for experimental errors.

Binomial Distribution↗
PubMed1991

The role of positive and negative interspecific associations in the organization of communities of intestinal helminths of bats.

Twelve populations of bats were examined to determine the extent of interspecific associations in determining the species richness of intestinal helminth infracommunities. The pool of helminth species which was available to individual bats ranged from 2 to 21. The 'summed binomial' distribution was determined to underlie the host frequency distribution of the number of helminth species per host. Overall covariation in occurrences of species in replicated communities can be detected by testing for the equality of the observed variance of the host frequency distribution to the variance expected when species are allocated to hosts at random. Where statistically significant the covariance was indicative of a majority of positive rather than negative interspecific associations. As the mean number of species per host in a host population increases not only does the number of positive associations increase but so does the proportion of species pairs which exhibit positive associations. Although there is an increase in the proportion of species pairs which exhibit positive associations as the number of species increases, the magnitude of the associations (as indicated by the mean positive or the mean negative pairwise covariances) does not. Therefore, we concluded that positive interactions are more common than negative interactions in determining the species richness of helminth infracommunities of bats. Further, positive associations become even more important as the community becomes more complex. However, the increased importance is derived from the number rather than the strength of the associations.

Animals↗
PubMed2002

The illusion of the learning phase for lymphatic mapping.

BACKGROUND: We provide a statistical analysis of the learning phase for sentinel node biopsy. METHODS: Four learning phases were analyzed: 25, 50, 75, and 150 procedures with a corresponding number of 10, 20, 30, and 60 tumor-positive cases. Critical values of nonidentification rate and false-negative rate were defined. The binomial distribution was used to calculate the probabilities of correctly or incorrectly accepting the quality of the performance, given a certain long-term nonidentification or false-negative rate. RESULTS: The chance of incorrectly reaching a favorable false-negative rate of <10% (critical value) in 20 metastasized patients was 18% for a surgeon with a long-term probability of false-negative procedures of 15%. This chance was reduced to 10% with a learning phase of 60 tumor-positive cases. When this chance has to be further reduced to 5%, the critical value has to be lower in smaller groups of patients: 5% false-negative rate in 20 tumor-positive procedures. CONCLUSIONS: A learning phase of at least 150 procedures with 60 tumor-positive cases is needed to draw any reliable conclusion about the quality of sentinel node biopsy. In general, a compromise has to be made between the reliability of the results and the practically achievable number of procedures.

Binomial Distribution↗
PubMedDate not supplied

Development of probabilistic tools to assist in the establishment and management of cryopreserved plant germplasm collections.

A simple method, based on the binomial distribution, is proposed to calculate the probability of recovering at least one (or any other fixed number of) plant(s) from a cryobank sample using four given parameters: the percentage of plant recovery observed from a control sample, pobs, the number of propagules used for this control, n1, the number of propagules in the cryobank sample, n2, a chosen risk for the calculation of a confidence interval for the observed plant recovery, alpha. Using this method, it is possible to assess the number of propagules which should be rewarmed immediately after freezing in order to estimate the plant recovery percentage as a function of the total number of propagules available. It also allows the calculation of the minimum plant recovery percentage to ensure that the probability to recover at least one (or A, with A>1) plant(s) is higher than a fixed probability level, as a function of the control and the cryobank sample sizes. Reciprocally, once the plant recovery percentage has been estimated, it is possible to assess the minimum size of the cryobank sample to obtain a probability to recover at least one (or A, with A>1) plant(s) higher than some fixed level.

Binomial Distribution↗
PubMed1986

On estimating canopy photosynthesis and stomatal conductance in a deciduous forest with clumped foliage.

The foliage in a fully-leafed deciduous forest canopy is clumped. Consequently, theory indicates that the probability of beam penetration will be estimated more accurately with a model based on the negative binomial distribution than with a model based on the Poisson distribution, incorporating an assumption of a spherical leaf inclination angle distribution. Flux densities of photosynthetically active radiation (PAR) were measured in and above a deciduous forest canopy and were computed with the canopy radiative transfer models based on the negative binomial and Poisson distributions. These radiation values were used to compute canopy photosynthesis and stomatal conductance. Canopy photosynthesis and stomatal conductance, based on the negative binomial model, overestimated values computed from measured PAR profiles by 8 and 9%. respectively. The canopy photosynthesis and stomatal conductance values computed with the spherical Poisson model under-estimated measured values by 17 and 10%, respectively. Thus, the negative binomial radiative transfer model improves estimates of canopy photosynthesis and, to a lesser extent, stomatal conductance, inside a deciduous forest.

Journal Article↗
PubMed1998

The incidence of sheep strike by Lucilia sericata on sheep farms in Britain: a simulation model.

Using a combination of a temperature-dependent simulation of the population dynamics of Lucilia sericata and a logistic model of sheep susceptibility, based on patterns of faecal soiling, fleece length and fleece humidity, a deterministic simulation model has been constructed to predict the incidence of sheep strike by L. sericata on lambs and ewes in Britain. Strikes are assigned to individual sheep in the flock according to a negative binomial distribution. The model shows that the majority of the first strikes of the season occur equally on ewes and lambs, when ewe fleeces are long and before lamb susceptibility increases though faecal soiling. With each subsequent generation of gravid blowflies, however, a greater proportion of strikes occur on lambs, while the number of strikes observed on ewes remains relatively consistent throughout the season. The increase in strike of lambs is due to the seasonal increase in lamb faecal soiling, associated with rising helminth infections and lamb fleece growth. The model shows that at the beginning of the season the incidence of strike is limited by the low number of flies present: towards the end of seasons, however, the blowfly population had grown large enough for the number of strikes to be limited by the number of susceptible ewes and lambs. The model shows that the seasonal incidence of strike is highly sensitive to the interactions between temperature, rainfall and would length. Strike was most prevalent under warm, wet conditions. However, there is a critical period during spring, where the short fleeces of lambs and ewes, in the latter case due to shearing, results in the desiccation of egg batches. If this coincides with dry conditions, the high levels of mortality result in suppression of the fly population and a reduction in the subsequent incidence of strike.

Animals↗
PubMed1989

[An analysis of the functional heterogeneity of the sensory motor neuron synapse of the frog].

Four models of the amplitude fluctuations of postsynaptic potentials have been compared. Better agreement of convolution of the two binomial distributions and beta-model as compared to the binomial model is demonstrated. The beta-model is based on the assumption that the probability of the transmitter quantum release is a random variable which has beta distribution. The number of the quantum generators estimated by the beta-model is close to the number of synaptic boutons in the sensory-motor synapses of the frog. Investigation of this model has shown that the number of generators estimated by the binomial model may be interpreted as the number of transmitter release sites functioning with probabilities exceeding 0.2. Results obtained confirm the hypothesis concerning the functional heterogeneity of release sites at the frog interneuronal synapses.

Animals↗
PubMed1993

The application of mitochondrial DNA typing to the study of white Caucasian genetic identification.

Mitochondrial DNA (mtDNA) from 100 unrelated British White Caucasians was extracted, amplified and directly sequenced. Sequences of approximately 800 nucleotides were obtained from 2 hypervariable segments within the non-coding region of the mitochondrial genome. A total of 91 different sequences were observed with an average nucleotide diversity of 1.1%. The most diverse pair of sequences differed at 3.6% of their nucleotide (nt) sites. Comparison to a consensus reference sequence showed that each region was polymorphic to a similar extent. Different methods of genetic analysis were used to examine the variation in each region, including pairwise comparisons, which demonstrated that although the data did not fit a Poisson distribution, the fit was closer to a Negative Binomial distribution.

Base Sequence↗
PubMed1994

[The human factor in accidents].

Data on accidents at work and traffic accidents in different countries are discussed. Comparison of the number of war victims and victims of accidents shows the latter to be more numerous. Public opinion towards is less negative than towards several infectious diseases. The reason for this is the (wrong) opinion that people can prevent getting involved in an accident. There are many reasons why the progress in our knowledge of the phenomenon of accidents has not been faster. The distribution of accidents does not fit the model of chance distribution, but it fits quite well into negative binomial distribution, which is a model of "unequal accident proneness" hypothesis. The term "accident proneness" originated as a result of controversy between European (Eysenck, Shaw and others) and American (Suchman, Haight and others) psychologists. Today, the discrepancy in the attitudes has come to be much slighter because of the more dynamic and situational approach to the phenomenon of "accident proneness". The phenomenon is defined as possession of the qualities that are harmful to safe work at a certain moment or/and lack of possession of the qualities that are indispensable for safe work at that same moment. Certain factors associated with "accident proneness", however, are stable and general: personality and sex. Some are prone to changing slowly during one's lifetime: age and experience. Many are accidental: alcohol, illness, fatigue, mood etc. Ramsey's model of accident proneness in presented in more detail. The model includes interaction between man and an objective situation at different levels: cognitive, conative and psychomotor.

Accident Proneness↗
PubMed1986

Distribution of episodes of mental illness in general practice: results from the Second National Morbidity Survey.

The Second National Morbidity Survey, conducted in England and Wales between 1970 and 1976, contains a unique body of information on episodes of mental illness experienced by individuals registered in a representative sample of general practices around the country. This information is used to construct the episode distribution among the individuals surveyed. The Poisson and negative binomial distributions are then used to model the episodes. The Poisson model gives a very poor fit but the negative binomial model is found to fit the data very well. Deviations of the observed data from this model are discussed. The possibility of applying this model at the local practice level is then considered.

England↗
PubMed2004

Novel moment closure approximations in stochastic epidemics.

Moment closure approximations are used to provide analytic approximations to non-linear stochastic population models. They often provide insights into model behaviour and help validate simulation results. However, existing closure schemes typically fail in situations where the population distribution is highly skewed or extinctions occur. In this study we address these problems by introducing novel second- and third-order moment closure approximations which we apply to the stochastic SI and SIS epidemic models. In the case of the SI model, which has a highly skewed distribution of infection, we develop a second-order approximation based on the beta-binomial distribution. In addition, a closure approximation based on mixture distribution is developed in order to capture the behaviour of the stochastic SIS model around the threshold between persistence and extinction. This mixture approximation comprises a probability distribution designed to capture the quasi-equilibrium probabilities of the system and a probability mass at 0 which represents the probability of extinction. Two third-order versions of this mixture approximation are considered in which the log-normal and the beta-binomial are used to model the quasi-equilibrium distribution. Comparison with simulation results shows: (1) the beta-binomial approximation is flexible in shape and matches the skewness predicted by simulation as shown by the stochastic SI model and (2) mixture approximations are able to predict transient and extinction behaviour as shown by the stochastic SIS model, in marked contrast with existing approaches. We also apply our mixture approximation to approximate a likelihood function and carry out point and interval parameter estimation.

Computer Simulation↗
PubMed2000

Timing of insemination relative to ovulation in pigs: effects on sex ratio of offspring.

The objective of the present study was to identify effects of the interval between insemination and ovulation in pigs on the sex ratio and sex ratio dispersion of offspring. Crossbred sows that had farrowed 2 to 9 litters were weaned (Day 0) and came into estrus between Days 3 and 7 after weaning. Ultrasonography was performed every 6 h, from 12 h after the onset of estrus until ovulation had been observed. The sows were inseminated once at various intervals from the onset of estrus. At farrowing, the numbers of viable piglets and dead piglets were recorded per sow. In four 12-h intervals between insemination and ovulation (36 to 24 h before ovulation, 24 to 12 h before ovulation, 12 to 0 h before ovulation and 0 to 12 h after ovulation), the total number of piglets was (mean+/-SEM) 10.8+/-1.2 (n=15); 13.4+/-0.7 (n=23); 13.2+/-0.9 (n=21); and 12.1+/-1.0 (n=16), respectively (P>0.05). The percentage of male piglets per litter in the four 12-h intervals was 52.1+/-3.6, 50.5+/-2.7, 54.9+/-2.8 and 47.8+/-4.5, respectively (P>0.05). Sex ratio was not influenced by litter size (P>0.05), and its distribution was normally dispersed (i.e., as expected under a binomial distribution) in all 4 intervals between insemination and ovulation (P>0.05).

Animals↗
PubMed1997

Evolutionary distances between nucleotide sequences based on the distribution of substitution rates among sites as estimated by parsimony.

The rate of evolution of macromolecules such as ribosomal RNAs and proteins varies along the molecule because structural and functional constraints differ between sites. Many studies have shown that ignoring this variation in computing evolutionary distances leads to severe underestimation of sequence divergences, and thus can lead to misleading evolutionary tree inferences. We propose here a new parsimony-based method for computing evolutionary distances between pairs of sequences that takes into account this variation and estimates it from the data. This method applies to the number of substitutions per site in ribosomal RNA genes as well as to the number of nonsynonymous substitutions per codon for protein-coding genes and is especially suitable when large data sets (> or = 100 sequences) are analyzed. First, starting from a phylogeny constructed with usual distances, the maximum-parsimony method is used to infer the distribution of the number of substitutions that have occurred at each site (or codon) along this tree. This distribution is then fitted to an "invariant + truncated negative binomial" distribution that allows for invariant sites. Maximum-likelihood fitting of this distribution to different data sets showed that it agreed very well with real data. Noticeably, allowing for invariant sites seemed to be very important. Finally, two distance estimates were developed by introducing the distribution of site variability into the substitution models of Jukes and Cantor and of Kimura. The use of different numbers of aligned sequences (up to 1,000 rRNA sequences) showed that the parameters of the model are very sensitive to the number of sequences used to estimate them. However, if at least 100 sequences are considered, the two new distance estimates are quite stable with respect to the number of sequences used to fit the distribution. This stability is true for low as well as for high evolutionary distances. These new distances appeared to be much better estimates of the number of substitutions per site than the classical distances of Jukes and Cantor and of Kimura, which both greatly underestimate this number, so that they can serve as indexes to detect saturation. We conclude that the new distances are particularly suitable for phylogenetic analysis when very distantly related species and relatively large data sets are considered. Trees reconstructed using these distances are generally different from those constructed by means of the classical estimates. Using this new method, we showed that the mean evolutionary distance between Prokaryotes and Eukaryotes is substantially higher for the small-subunit than for the large-subunit rRNAs. This suggests than the former might have experienced a drastic change during the early evolution of Eukaryotes.

Algorithms↗
PubMed1995

Subunit-dependent assembly of inward-rectifier K+ channels.

Inward-rectifier, G-protein-regulated and ATP-dependent K+ channels form a novel gene family of related proteins which share two transmembrane segments as a common structural feature. These K+ channels are only distantly related to the voltage-gated Shaker-type K+ channels comprising six transmembrane segments. Although the quaternary structure of voltage-gated K+ channels has been extensively studied in the past, little is known about subunit assembly of inward-rectifier K+ channels. Differential sensitivity of inward-rectifier K+ channels to voltage-dependent pore block by spermine was used to analyse subunit assembly. It is shown that inward-rectifier K+ channel proteins are composed of four subunits whose assembly obeys the rules of a binomial distribution. 'Strong' and 'mild' inward-rectifier K+ channel subunits (BIR10 and ROMK1) which are co-expressed in individual auditory hair cells form hetero-tetramers. Distribution of these hetero-tetramers, however, is not binomial. Hetero- and homo-oligomeric channels form with similar probabilities resulting in independent channel populations with distinct functional properties.

Adenosine Triphosphate↗
PubMed1974

All-or-none-acquisition in matching-to-sample and a test of two models.

Three pigeons learned to match three colors in a matching-to-sample procedure. The sample hue was presented on the center one of three keys, and the comparison hues were presented on the side keys. Forty responses on the center key produced the stimuli on the side keys and left the sample on the center key. A single response on the correct side key produced 3-sec access to grain, which was followed by a 25-sec intertrial interval. A correction procedure was employed when an error was committed. Before attaining asymptotic levels, there was no evidence of learning, responses were independent of the preceding response, and distributions of errors in four-trial blocks were binomial. Distributions of error runs, runs of various lengths, autocorrelations of errors of several lags, alternations of correct responses and errors, etc., were shown to fit Bower's (1961) all-or-none model better than a gradual learning model of Bush and Sternberg (1959). A transfer test employing a novel color showed only transitory degradation of performance.

Journal Article↗
PubMed1975

Chromosome aberrations in human lymphocytes after irradiation with 15.0-MeV neutrons in vitro. II. Analysis of the number of absorption events and the interaction distance in the formation of dicentric chromosomes.

The rejoining distance for the formation of dicentric chromosomes in human lymphocytes after irradiation with 15.0-MeV neutrons has been derived on the basis of microdosimetric concepts. For the formation of a dicentric chromosome, primary lesions produced by absorption events can interact within the nucleus over a distance of at least I.8 mum. The mean number of absorption events within this range is lower than for sparsely ionizing radiation. The intercellular distribution of dicentric chromosomes is consistent with a negative binomial distribution.

Cell Nucleus↗