Binomial Distribution (binomial + distribution)

Distribution by Scientific Domains

Kinds of Binomial Distribution

  • negative binomial distribution


  • Selected Abstracts


    Designing Accurate Control Charts Based on the Geometric and Negative Binomial Distributions

    QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2005
    Neil C. Schwertman
    Abstract Attribute control charts are used effectively to monitor for process change. Their accuracy can be improved by judiciously selecting the sample size. The required sample sizes to achieve accuracy can be quite restrictive, especially when the nominal proportions of non-conforming units are quite small. The usual attribute control chart has a set sample size and the number of non-conforming units in the sample is plotted. If, instead of setting a specific sample size the number of non-conforming units is set, an alternative monitoring process is possible. Specifically, the cumulative count of conforming (CCC- r) control chart is a plot of the number of units that must be tested to find the rth non-conforming unit. These charts, based on the geometric and negative binomial distributions, are often suggested for monitoring very high quality processes. However, they can also be used very efficiently to monitor processes of lesser quality. This procedure has the potential to find process deterioration more quickly and efficiently. Xie et al. (Journal of Quality and Reliability Management 1999; 16(2):148,157) provided tables of control limits for CCC- r charts for but focused mainly on high-quality processes and the tables do not include any assessments of the risk of a false alarm or the reliability of detecting process change. In this paper, these tables are expanded for processes of lesser quality and include such assessments using the number of expected monitoring periods (average run lengths (ARLs)) to detect process change. Also included is an assessment of the risk of a false alarm, that is, a false indication of process deterioration. Such assessments were not included by Xie et al. but are essential for the quality engineer to make sound decisions. Furthermore, a hybrid of the control charts based on the binomial, geometric and negative binomial distributions is proposed to monitor for process change. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Comparison of Additional Costs for Several Replacement Strategies of Randomly Ageing Reinforced Concrete Pipes

    COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 7 2009
    Franck Schoefs
    Some of them carry seawater and can deteriorate with time because of internal corrosion. Because of the low O2 content of aggressive water, slow corrosion is expected for such applications. If the RCPs are not periodically replaced, they will eventually fail. Replacement strategies for these pipes depend on (1) the risks associated with the failure of the water distribution network, and (2) the costs associated with replacing the pipes, including the removal of existing pipes, installation of new pipes, and associated production losses. Because of the lack of statistical data regarding RCP failure, the development of a risk-based replacement strategy is not an easy task. This article demonstrates how predictive models for the evolution of the failure of RCPs and the associated consequences of failure can be used to develop risk-based replacement strategies for RCPs. An application for the replacement strategies of a network modeled as a system consisting of 228 RCPs is presented as a case study. We focus on the assessment of the number of replaced components that governs the costs. The main objective of this article is to provide a theoretical approach for comparing replacement strategies, based on (1) the results of a reliability study, (2) the representation of the distributions of failed components (binomial distribution), and (3) the decision tree representation for replacement of RCPs. A focus on the scatter of the induced costs themselves is suggested to emphasize the financial risk. [source]


    Predicting global abundance of a threatened species from its occurrence: implications for conservation planning

    DIVERSITY AND DISTRIBUTIONS, Issue 1 2009
    Marcos S. L. Figueiredo
    Abstract Aim, Global abundance is an important characteristic of a species that is correlated with geographical distribution and body size. Despite its importance these estimates are not available since reliable field estimates are either expensive or difficult to obtain. Based on the relationship between a species' local abundance and distribution, some authors propose that abundance can be obtained through spatial distribution data from maps plotted at different scales. This has never been tested over the entire geographical range of a species. Thus, the aim of this study was to estimate global abundance of the Neotropical primate Brachyteles hypoxanthus (northern muriqui) and compare the results with available field estimates. Location, From southern Bahia to Minas Gerais and Espírito Santo states, in the Brazilian Atlantic rain forest. Methods, We compiled 25 recent occurrence localities of B. hypoxanthus and plotted them in grid cells of five different sizes (1, 25, 50, 75 and 100 km per side) to evaluate the performance and accuracy of abundance estimates over a wide range of scales. The abundance estimates were obtained by the negative binomial distribution (NBD) method and corrected by average group size to take into account primate social habits. To assess the accuracy of the method, the predicted abundances were then compared to recent independent field estimates. Results, The NBD estimates were quite accurate in predicting B. hypoxanthus global abundance, once the gregarious habits of this species are taken into account. The predicted abundance estimates were not statistically different from those obtained from field estimates. Main conclusions, The NBD method seems to be a quick and reliable approach to estimate species abundance once several limiting factors are taken into account, and can greatly impact conservation planning, but further applications in macroecological and ecological theory testing needs improvement of the method. [source]


    Measures, perceptions and scaling patterns of aggregated species distributions

    ECOGRAPHY, Issue 1 2010
    Cang Hui
    Non-random (aggregated) species distributions arise from habitat heterogeneity and nonlinear biotic processes. A comprehensive understanding of the concept of aggregation, as well as its measurement, is pivotal to our understanding of species distributions and macroecological patterns. Here, using an individual-based model, we analyzed opinions on the concept of aggregation from the public and experts (trained ecologists), in addition to those calculated from a variety of aggregation indices. Three forms of scaling patterns (logarithmic, power-law and lognormal) and four groups of scaling trajectories emerged. The experts showed no significant difference from the public, although with a much lower deviation. The public opinion was partially influenced by the abundance of individuals in the spatial map, which was not found in the experts. With the increase of resolution (decrease of grain), aggregation indices showed a general trend from significantly different to significantly similar to the expert opinion. The over-dispersion index (i.e. the clumping parameter k in the negative binomial distribution) performed, at certain scales, as the closest index to the expert opinion. Examining performance of aggregation measures from different groups of scaling patterns was proposed as a practical way of analyzing spatial structures. The categorization of the scaling patterns of aggregation measures, as well as their over- and in-sensitivity towards spatial structures, thus not only provides a potential solution to the modifiable areal unit problem, but also unveils the interrelationship among the concept, measures and perceptions of aggregated species distributions. [source]


    Transmission dynamics of an iridescent virus in an experimental mosquito population: the role of host density

    ECOLOGICAL ENTOMOLOGY, Issue 4 2005
    Carlos F. Marina
    Abstract., 1.,The transmission of insect pathogens cannot be adequately described by direct linear functions of host and pathogen density due to heterogeneity generated from behavioural or physiological traits, or from the spatial distribution of pathogen particles. Invertebrate iridescent viruses (IIVs) can cause patent and lethal infection or a covert sub-lethal infection in insects. Aedes aegypti larvae were exposed to suspensions of IIV type 6 at two densities. High larval density increased the prevalence of aggression resulting in potentially fatal wounding. 2.,The overall prevalence of infection (patent + covert) was positively influenced by host density and increased with exposure time in both densities. The survival time of patently infected insects was extended by , 5 days compared with non-infected insects. 3.,Maximum likelihood models based on the binomial distribution were fitted to empirical results. A model incorporating heterogeneity in host susceptibility by inclusion of a pathogen-free refuge was a significantly better fit to data than an all-susceptible model, indicating that transmission is non-linear. The transmission coefficient (,) did not differ with host density whereas the faction of the population that occupied the pathogen-free refuge (,R) was significantly reduced at high host density compared with the low density treatment. 4.,The transmission of free-living infective stages of an IIV in Ae. aegypti larvae is non-linear, probably because of density-related changes in the frequency of aggressive encounters between hosts. This alters host susceptibility to infection and effectively reduces the proportion of hosts that occupy the pathogen-free refuge. [source]


    The role of resources and natural enemies in determining the distribution of an insect herbivore population

    ECOLOGICAL ENTOMOLOGY, Issue 2 2001
    Iain S. Williams
    Summary 1. Both resources and natural enemies can influence the distribution of a herbivore. The ideal free distribution predicts that herbivores distribute themselves to optimise utilisation of resources. There is also evidence of herbivores seeking out refuges that reduce natural enemy attack (enemy-free space). Which of these theories predominates in a thistle,tephritid Terellia ruficauda (Diptera: Tephritidae),parasitoid interaction is examined. 2. The plant, Cirsium palustre, had a contagious distribution approximated by the negative binomial distribution. Terellia ruficauda foraged preferentially and oviposited on isolated plants although its larvae gained neither nutritional benefit nor reduced natural enemy pressure from such behaviour. 3. Parasitoids of T. ruficauda foraged and oviposited more frequently on isolated than on crowded T. ruficauda, resulting in inverse density-dependent parasitoid attack at all spatial scales examined. Neither the herbivore nor natural enemies distributed themselves according to the predictions of the ideal free distribution and the herbivore did not oviposit to reduce natural enemy attack. 4. Extrapolating from the theoretical predictions of the ideal free distribution and enemy-free space to the field requires considerable caution. Terellia ruficauda and its parasitoids appear to select their oviposition sites to spread the risk of losses through factors (e.g. mammal herbivory) that may damage dense clusters of C. palustre. [source]


    Evaluation of water quality using acceptance sampling by variables

    ENVIRONMETRICS, Issue 4 2003
    Eric P. Smith
    Abstract Under section 303(d) of the Clean Water Act, states must identify water segments where loads of pollutants are violating numeric water quality standards. Consequences of misidentification are quite important. A decision that water quality is impaired initiates the total maximum daily load or TMDL planning requirement. Falsely concluding that a water segment is impaired results in unnecessary TMDL planning and pollution control implementation costs. On the other hand, falsely concluding that a segment is not impaired may pose a risk to human health or to the services of the aquatic environment. Because of the consequences, a method is desired that minimizes or controls the error rates. The most commonly applied approach is to use the Environmental Protection Agency (EPA)'s raw score approach in which a stream segment is listed as impaired when greater than 10 per cent of the measurements of water quality conditions exceed a numeric criteria. An alternative to the EPA approach is the binomial test that the proportion exceeding the standard is 0.10 or less. This approach uses the number of samples exceeding the criteria as a test statistic along with the binomial distribution for evaluation and estimation of error rates. Both approaches treat measurements as binary; the values either exceed or do not exceed the standard. An alternative approach is to use the actual numerical values to evaluate standard. This method is referred to as variables acceptance sampling in quality control literature. The methods are compared on the basis of error rates. If certain assumptions are met then the variables acceptance method is superior in the sense that the variables acceptance method requires smaller sample sizes to achieve the same error rates as the raw score method or the binomial method. Issues associated with potential problems with environmental measurements and adjustments for their effects are discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Distributional Patterns of Diatoms and Limnodrilus Oligochaetes in a Kenyan Dry Streambed Following the 1999,2000 Drought Conditions

    INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2005
    Jude M. Mathooko
    Abstract Drought is a natural phenomenon experienced by many intermittent and also seasonal lotic systems. It has diverse effects on the structure and distribution of biological communities through habitat transition from wetted to terrestrial conditions. The Njoro River, a tropical stream, was drought-stressed between late 1999 and mid 2000, providing an opportunity to sample and describe the distributional patterns of diatoms and Limnodrilus oligochaetes in the vertical sediment profile. The dispersion of Limnodrilus oligochaetes with sediment depth profile varied from quasi-random (i.e. exponent k of the negative binomial distribution >2.0 or <0) at the surface to strong aggregation (0 < k < 1.0) in the deeper sediments. Diatoms were heterogenous, with most species contributing less than 1% of all the diatoms collected from the riverbed. Contagious dispersion was a common feature among the diatom species. The distribution of Fragilaria ulna was largely quasi-random in all sites, with Nitzschia amphibia and Cocconeis placentula demonstrating quasi-random distribution in the Kerma vertical sediment profile. Escape from stranding to deeper sediment strata as the drought progressed was not a universal response among the diatom species. Our results showed that drought-stress altered the structure of biological assemblages and also emphasized the need for the management of tropical lotic systems and their catchments for flow permanence. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Predicting abundance from occupancy: a test for an aggregated insect assemblage

    JOURNAL OF ANIMAL ECOLOGY, Issue 3 2003
    M. Warren
    Summary 1The ubiquitous, positive abundance-occupancy relationship is of potential value to conservation and pest management because of the possibility of using it to predict species abundance from occupancy measures. 2He & Gaston (2000a) developed a model, and a parameterization method, for the prediction of abundance from occupancy based on the negative binomial distribution. There are to date few empirical tests of either the estimation method or model. Here we conduct such a test in a field-based mesocosm experiment using a Drosophilidae assemblage associated with decaying fruit. 3With individual (and groups of) fruit as minimum mapping units, abundance estimates derived using the parameterization method of the He-Gaston model differed significantly from measured values, and were least accurate for the most abundant species. 4Substitution of k -values corrected for species density in the model did not improve abundance predictions significantly. However, substitution of k -values calculated directly from the negative binomial distribution yielded highly accurate abundance predictions. 5Although the distribution of fly species did not deviate significantly from the negative binomial distribution, and the finest possible minimum mapping units were used (individual fruit), the parameterization method in the He-Gaston model consistently underestimated the abundance of species in the assemblage because individuals were very highly aggregated within fruit. 6Because of its potential importance, this model and parameterization method require further exploration at fine scales, commonly represented by individual habitat units, for highly aggregated species. The incorporation of spatially explicit information may provide a means of improving abundance predictions in this regard. [source]


    Sampling plan for the coffee leaf miner Leucoptera coffeella with sex pheromone traps

    JOURNAL OF APPLIED ENTOMOLOGY, Issue 6 2008
    T. Bacca
    Abstract The population density of the coffee leaf miner Leucoptera coffeella (Guérin-Méneville & Perrottet) (Lep., Lyonetiidae) can be estimated using pheromone traps in coffee fields as male capture reflects this pest damage based on previous correlational study. However, the spatial distribution of pheromone traps and their density are necessary to optimize the sampling procedure with pheromone traps. Therefore, the objectives of the present study were to determine the pheromone trap density required per hectare to sample coffee leaf miner populations and to determine the spatial distribution of the males of this pest species. The males were sampled every 8 days in 12 consecutive evaluations. Taylor's power law and frequency distributions were used to recognize the distribution of the male capture data, which followed a negative binomial distribution. A common K was obtained, allowing the establishment of a single conventional sampling plan for the 12 fields investigated. The adjusted sampling plan requires eight traps in an area of 30 ha for a 25% precision error. Kriging-generated maps allowed the simulation of male captures for 8, 12 and 20 traps per 30 ha and the results were compared with those obtained with absolute sampling resulting in R2 -values of 0.30, 0.57 and 0.60 respectively. The traps were able to identify the more highly infested areas within the field and are a precise and efficient tool for sampling populations of L. coffeella. [source]


    Nestling sex ratio of golden-winged warblers Vermivora chrysoptera in an introgressed population

    JOURNAL OF AVIAN BIOLOGY, Issue 6 2008
    Kate J. Neville
    Sex ratio biases in avian species remain controversial, although several studies have documented apparent facultative adjustment of offspring sex ratios. While hybridizing pied and collared flycatchers have exhibited sex ratio skews that may be a response to sex-based costs associated with hybridization, this appears not to be true of a hybridized population of blue-winged Vermivora pinus and golden-winged V. chrysoptera warblers. We examined the primary sex ratio of nestlings in a population of hybrid and introgressed golden-winged warblers. The sex ratio of 298 nestlings from 81 nests in the population was approximately 50:50. We conducted paternity assignments and analyzed groups of nestlings with shared genetic parents ("genetic broods") and found no difference from the expected binomial distribution, and no statistically significant relationship between parental species phenotype and nestling sex ratio. We saw no evidence of preferential production of male or female nestlings, and female hybrids were found to mate and breed in the population. This suggests that heterogametic (female) hybrids are both viable and fertile, and thus that Haldane's Rule does not apply to this system. While populations of hybridizing golden-winged warblers should be monitored for evidence of costs of heterospecific pairings, it is unlikely that adjustment of sex ratios would be the form of compensation for sub-optimal mating conditions. Our results provide support for the emerging hypothesis that hybrids suffer no disadvantage relative to golden-winged and blue-winged warblers. [source]


    Sex allocation in black-capped chickadees Poecile atricapilla

    JOURNAL OF AVIAN BIOLOGY, Issue 2 2003
    Scott M. Ramsay
    Optimal sex allocation for individuals can be predicted from a number of different hypotheses. Fisherian models of sex allocation predict equal investment in males and females up to the end of parental care and predict brood compositions based on the relative costs of producing males and females. The Trivers-Willard hypothesis predicts that individual females should alter the sex ratio of their broods based on their own condition if it has a differential impact on the lifetime reproductive success of their sons and daughters. The Charnov model of sex allocation predicts that females should alter sex allocation based on paternal attributes that may differentially benefit sons versus daughters. Because females are the heterogametic sex in birds, many recent studies have focussed on primary sex ratio biases. In black-capped chickadees Poecile atricapilla, males are larger than females suggesting they may be more costly to raise than females. Female condition affects competitive ability in contests for mates, and thus may be related to variance in fecundity. Females prefer high-ranking males as both social and extrapair partners. These observations suggest that females might vary the sex ratio of their broods based on the predictions of any of the above models. Here, we report on the results of PCR based sex determination of 1093 nestlings in 175 broods sampled from 1992 to 2001. Population-wide, we found a mean brood sex ratio of 0.525±0.016, with no significant deviation from a predicted binomial distribution. We found no effect of clutch size, female condition, hatch date, parental rank or paternity. Our results reject the idea that female black-capped chickadees systematically vary sex allocation in their broods. [source]


    Absence of seasonal variation in great tit offspring sex ratios

    JOURNAL OF AVIAN BIOLOGY, Issue 2 2002
    Nanette Verboven
    When the timing of breeding affects the reproductive value of sons and daughters differently, parents are expected to increase their fitness by changing the offspring sex ratio during the course of the breeding season. Previous studies have shown that in great tits Parus major hatching date has a stronger effect on the fitness of juvenile males than on that of juvenile females. We tested whether this difference was reflected in a seasonal decline in the proportion of sons per breeding attempt. Although offspring sex ratio was more variable than would be expected from a binomial distribution, there was no significant relationship between the proportion of sons and the laying date of the clutch. Moreover, individual females did not adjust the sex ratio of their offspring following an experimental delay of breeding. This study therefore fails to demonstrate adaptive seasonal variation in great tit offspring sex ratios. [source]


    Nestling sex ratios in a population of Bluethroats Luscinia svecica inferred from AFLPÔ analysis

    JOURNAL OF AVIAN BIOLOGY, Issue 1 2000
    S. Questiau
    We studied the sex ratio of Bluethroat Luscinia svecica broods using AFLPs. Our aim was to test whether there is a bias towards males that could be explained by sexual selection theories, or conversely, a bias towards females that could help explain the female-biased sex ratio among juveniles observed at a wintering site. The AFLP technique was reliable in sexing the nestlings from even small initial DNA quantities. Given the large number of polymorphic markers that can be obtained for each primer combination, the probability of detecting a W-chromosome-linked fragment is reasonably high. As a consequence, this method could be used in other species for sex-ratio studies and for other genetic purposes. Among 246 nestlings, we found an overall proportion of males of 50.8% at hatching and the sex-ratio variation using broods as independent units was not significantly different from expectation under a binomial distribution. None of the parental and environmental variables tested changed significantly the deviance to the model. Thus, sex determination in the Bluethroat seems to match the classical Mendelian model of a 1:1 sex ratio and cannot explain the biased sex ratio towards juvenile females found at the wintering site. [source]


    Interspecific variation in primary seed dispersal in a tropical forest

    JOURNAL OF ECOLOGY, Issue 4 2008
    Helene C. Muller-Landau
    Summary 1We investigated the relationships of seed size, dispersal mode and other species characteristics to interspecific variation in mean primary seed dispersal distances, mean annual seed production per unit basal area, and clumping of seed deposition among 41 tropical tree species on Barro Colorado Island, Panama. 2A hierarchical Bayesian model incorporating interannual variation in seed production was used to estimate seed dispersal, seed production, and clumping of seed rain for each species from 19 years of data for 188 seed traps on a 50-ha plot in which all adult trees were censused every 5 years. 3Seed dispersal was modelled as a two-dimensional Student's T distribution with the degrees of freedom parameter fixed at 3, interannual variation in seed production per basal area was modelled as a lognormal, and the clumping of seed rain around its expected value was modelled as a negative binomial distribution. 4There was wide variation in seed dispersal distances among species sharing the same mode of seed dispersal. Seed dispersal mode did not explain significant variation in seed dispersal distances, but did explain significant variation in clumping: animal-dispersed species showed higher clumping of seed deposition. 5Among nine wind-dispersed species, the combination of diaspore terminal velocity, tree height and wind speed in the season of peak dispersal explained 40% of variation in dispersal distances. Among 31 animal-dispersed species, 20% of interspecific variation in dispersal distances was explained by seed mass (a negative effect) and tree height (a positive effect). 6Among all species, seed mass, tree height and dispersal syndrome explained 28% of the variation in mean dispersal distance and seed mass alone explained 45% of the variation in estimated seed production per basal area. 7Synthesis. There is wide variation in patterns of primary seed rain among tropical tree species. Substantial proportions of interspecific variation in seed production, seed dispersal distances, and clumping of seed deposition are explained by relatively easily measured plant traits, especially dispersal mode, seed mass, and tree height. This provides hope for trait-based generalization and modelling of seed dispersal in tropical forests. [source]


    Two New Statistics to Detect Answer Copying

    JOURNAL OF EDUCATIONAL MEASUREMENT, Issue 1 2003
    Leonardo S. Sotaridona
    Two new indices to detect answer copying on a multiple-choice test,S1 and S2,were proposed. The S1 index is similar to the K index (Holland, 1996) and the K2 index (Sotaridona & Meijer, 2002) but the distribution of the number of matching incorrect answers of the source and the copier is modeled by the Poisson distribution instead of the binomial distribution to improve the detection rate of K and K2. The S2 index was proposed to overcome a limitation of the K and K2 index, namely, their insensitiveness to correct answers copying. The S2 index incorporates the matching correct answers in addition to the matching incorrect answers. A simulation study was conducted to investigate the usefulness of S1 and S2 for 40- and 80-item tests, 100 and 500 sample sizes, and 10%, 20%, 30%, and 40% answer copying. The Type I errors and detection rates of S1 and S2 were compared with those of the K2 and the , copying index (Wollack, 1997). Results showed that all four indices were able to maintain their Type I errors, with S1 and K2 being slightly conservative compared to S2 and ,. Furthermore, S1 had higher detection rates than K2. The S2 index showed a significant improvement in detection rate compared to K and K2. [source]


    Industry Characteristics Linked to Establishment Concentrations in Nonmetropolitan Areas

    JOURNAL OF REGIONAL SCIENCE, Issue 2 2000
    Yunsoo Kim
    In this paper we investigate industry characteristics associated with the clustering of establishments in three-digit SIC manufacturing industries in nonmetropolitan areas. The dispersion parameter k of the negative binomial distribution is selected as the measure of industry spatial concentration. Associations between industry characteristics and spatial concentration are investigated using OLS regression analysis. Our findings indicate that the spatial clustering of establishments is positively related to industry average establishment size, reliance on natural resource inputs, labor intensity, cost shares of professional and technical employees, and cost shares of low-skilled workers. Agglomeration is negatively related to multiplant structure, employment in precision production, and reliance on local product and input markets. [source]


    COMPARISON OF METHODS FOR ANALYZING REPLICATED PREFERENCE TESTS

    JOURNAL OF SENSORY STUDIES, Issue 6 2005
    CHUN-YEN CHANG COCHRANE
    ABSTRACT Preference testing is commonly used in consumer sensory evaluation. Traditionally, it is done without replication, effectively leading to a single 0/1 (binary) measurement on each panelist. However, to understand the nature of the preference, replicated preference tests are a better approach, resulting in binomial counts of preferences on each panelist. Variability among panelists then leads to overdispersion of the counts when the binomial model is used and to an inflated Type I error rate for statistical tests of preference. Overdispersion can be adjusted by Pearson correction or by other models such as correlated binomial or beta-binomial. Several methods are suggested or reviewed in this study for analyzing replicated preference tests and their Type I error rates and power are compared. Simulation studies show that all methods have reasonable Type I error rates and similar power. Among them, the binomial model with Pearson adjustment is probably the safest way to analyze replicated preference tests, while a normal model in which the binomial distribution is not assumed is the easiest. [source]


    Distributional differences of the impact factor in the sciences versus the social sciences: An analysis of the probabilistic structure of the 2005 journal citation reports

    JOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 9 2008
    Stephen J. Bensman
    This paper examines the probability structure of the 2005 Science Citation Index (SCI) and Social Sciences Citation Index (SSCI) Journal Citation Reports (JCR) by analyzing the Impact Factor distributions of their journals. The distribution of the SCI journals corresponded with a distribution generally modeled by the negative binomial distribution, whereas the SSCI distribution fit the Poisson distribution modeling random, rare events. Both Impact Factor distributions were positively skewed,the SCI much more so than the SSCI,indicating excess variance. One of the causes of this excess variance was that the journals highest in the Impact Factor in both JCRs tended to class in subject categories well funded by the National Institutes of Health. The main reason for the SCI Impact Factor distribution being more skewed than the SSCI one was that review journals defining disciplinary paradigms play a much more important role in the sciences than in the social sciences. [source]


    Multilevel modelling of the number of property crimes: household and area effects

    JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 2 2006
    Andromachi Tseloni
    Summary., This study examines household and area effects on the incidence of total property crimes and burglaries and thefts. It uses data from the 2000 British Crime Survey and the 1991 UK census small area statistics. Results are obtained from estimated random-effects multilevel models, with an assumed negative binomial distribution of the dependent variable. Both household and area characteristics, as well as selected interactions, explain a significant portion of the variation in property crimes. There are also a large number of significant between-area random variances and covariances of household characteristics. The estimated fixed and random effects may assist in advancing victimization theory. The methods have potential for developing a better understanding of factors that give rise to crime and so assist in framing crime prevention policy. [source]


    Modelling species diversity through species level hierarchical modelling

    JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 1 2005
    Alan E. Gelfand
    Summary., Understanding spatial patterns of species diversity and the distributions of individ-ual species is a consuming problem in biogeography and conservation. The Cape floristic region of South Africa is a global hot spot of diversity and endemism, and the Protea atlas project, with about 60 000 site records across the region, provides an extraordinarily rich data set to model patterns of biodiversity. Model development is focused spatially at the scale of 1, grid cells (about 37 000 cells total for the region). We report on results for 23 species of a flowering plant family known as Proteaceae (of about 330 in the Cape floristic region) for a defined subregion. Using a Bayesian framework, we developed a two-stage, spatially explicit, hierarchical logistic regression. Stage 1 models the potential probability of presence or absence for each species at each cell, given species attributes, grid cell (site level) environmental data with species level coefficients, and a spatial random effect. The second level of the hierarchy models the probability of observing each species in each cell given that it is present. Because the atlas data are not evenly distributed across the landscape, grid cells contain variable numbers of sampling localities. Thus this model takes the sampling intensity at each site into account by assuming that the total number of times that a particular species was observed within a site follows a binomial distribution. After assigning prior distributions to all quantities in the model, samples from the posterior distribution were obtained via Markov chain Monte Carlo methods. Results are mapped as the model-estimated probability of presence for each species across the domain. This provides an alternative to customary empirical ,range-of-occupancy' displays. Summing yields the predicted richness of species over the region. Summaries of the posterior for each environmental coefficient show which variables are most important in explaining the presence of species. Our initial results describe biogeographical patterns over the modelled region remarkably well. In particular, species local population size and mode of dispersal contribute significantly to predicting patterns, along with annual precipitation, the coefficient of variation in rainfall and elevation. [source]


    Group inspection of dependent binary processes

    QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2009
    Christian H. Weiß
    Abstract We consider serially dependent binary processes, how they occur in several fields of practice. If such a process cannot be monitored continuously, because of process speed for instance, then one can analyze connected segments instead, where two successive segments have a sufficiently large time-lag. Nevertheless, the serial dependence has to be considered at least within the segments, i.e. the distribution of the segment sums is not binomial anymore. We propose the Markov binomial distribution to approximate the true distribution of the segment sums. Based on this distribution, we develop a Markov np chart and a Markov exponentially weighted moving average (EWMA) chart. We show how average run lengths (ARLs) can be computed exactly for both types of chart. Based on such ARL computations, we derive recommendations for chart design and investigate the out-of-control performance. A real-data example illustrates the application of these charts in practice. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    Phorbol esters and adenosine affect the readily releasable neurotransmitter pool by different mechanisms at amphibian motor nerve endings

    THE JOURNAL OF PHYSIOLOGY, Issue 2 2003
    T. J. Searl
    Phorbol esters and adenosine have been proposed to interact at common sites downstream of calcium entry at amphibian motor nerve endings. We thus studied the actions and interactions of phorbol esters and adenosine using electrophysiological recording techniques in conjunction with both binomial statistical analysis and high-frequency stimulation at the amphibian neuromuscular junction. To begin this study, we confirmed previous observations that synchronous evoked acetylcholine (ACh) release (reflected as endplate potentials, EPPs) is well described by a simple binomial distribution. We then used binomial analysis to study the effects of the phorbol ester phorbol dibutyrate (PDBu, 100 nm) and adenosine (50 µm) on the binomial parameters n (the number of calcium charged ACh quanta available for release) and p (the average probability of release), where the mean level of evoked ACh release (m) =np. We found that PDBu increased m by increasing the parameter n whilst adenosine reduced m by reducing n; neither agent affected the parameter p. PDBu had no effect on either the potency or efficacy of the inhibition produced by adenosine. Subtle differences between these two agents were revealed by the patterns of EPPs evoked by high-frequency trains of stimuli. Phorbol esters increased ACh release during the early phase of stimulation but not during the subsequent plateau phase. The inhibitory effect of adenosine was maximal at the beginning of the train and was still present with reduced efficacy during the plateau phase. When taken together with previous findings, these present results suggest that phorbol esters increase the immediately available store of synaptic vesicles by increasing the number of primed vesicles whilst adenosine acts at a later stage of the secretory process to decrease the number of calcium-charged primed vesicles. [source]


    Seasonal dynamics, dispersion, sequential sampling plans and treatment thresholds for the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in a mature lemon block in coastal New South Wales, Australia

    AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 3 2008
    Zhong Min Liu
    Abstract, Studies of citrus leafminer in a coastal orchard in NSW, Australia indicated that an increase in abundance to about one mine per flush was followed during the midseason flush by a rapid increase in population that was related to an increase in the percentage of leaves infested within flushes and the number of mines per leaf. The fits of frequency distributions and Iwao's patchiness regression indicated that populations were highly contagious initially, and as the exponent k of the negative binomial distribution increased with increasing population density, the distribution approached random. Concurrently, the coefficient of variation of mines per flush (which was strongly related to the proportion of un-infested flushes) decreased to about unity as the proportion of un-infested flushes reached zero and fell further as the number of mines per flush increased. Both numerative and binomial sequential sampling plans were developed using a decision threshold based on 1.2 mines per flush. The binomial sampling plan was based on a closely fitting model of the functional relationship between mean density and proportion of infested flushes. Functional relationships using the parameters determined from Iwao's patchiness regression and Taylor's power law were equally satisfactory, and one based on the negative binomial model also fitted well, but the Poisson model did not. The three best fitting models indicated that a decision threshold of 1.2 mines per flush was equivalent to 50% of flushes infested. From a practical point of view, the transition from 25% infestation of flushes through 50% is so rapid that it may be prudent to take action when the 25% level is reached; otherwise, the 50% may be passed before the crop is checked again. For valuable nursery stock should infestation be detected in spring, it may be advisable to apply prophylactic treatment as the midseason flush starts. [source]


    A Bayesian Long-term Survival Model Parametrized in the Cured Fraction

    BIOMETRICAL JOURNAL, Issue 3 2009
    Mário de Castro
    Abstract The main goal of this paper is to investigate a cure rate model that comprehends some well-known proposals found in the literature. In our work the number of competing causes of the event of interest follows the negative binomial distribution. The model is conveniently reparametrized through the cured fraction, which is then linked to covariates by means of the logistic link. We explore the use of Markov chain Monte Carlo methods to develop a Bayesian analysis in the proposed model. The procedure is illustrated with a numerical example. [source]


    Exact, Distribution Free Confidence Intervals for Late Effects in Censored Matched Pairs

    BIOMETRICAL JOURNAL, Issue 1 2009
    Shoshana R. Daniel
    Abstract When comparing censored survival times for matched treated and control subjects, a late effect on survival is one that does not begin to appear until some time has passed. In a study of provider specialty in the treatment of ovarian cancer, a late divergence in the Kaplan,Meier survival curves hinted at superior survival among patients of gynecological oncologists, who employ chemotherapy less intensively, when compared to patients of medical oncologists, who employ chemotherapy more intensively; we ask whether this late divergence should be taken seriously. Specifically, we develop exact, permutation tests, and exact confidence intervals formed by inverting the tests, for late effects in matched pairs subject to random but heterogeneous censoring. Unlike other exact confidence intervals with censored data, the proposed intervals do not require knowledge of censoring times for patients who die. Exact distributions are consequences of two results about signs, signed ranks, and their conditional independence properties. One test, the late effects sign test, has the binomial distribution; the other, the late effects signed rank test, uses nonstandard ranks but nonetheless has the same exact distribution as Wilcoxon's signed rank test. A simulation shows that the late effects signed rank test has substantially more power to detect late effects than do conventional tests. The confidence statement provides information about both the timing and magnitude of late effects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Is optimal foraging a realistic expectation in orb-web spiders?

    ECOLOGICAL ENTOMOLOGY, Issue 4 2009
    WILL EDWARDS
    Abstract 1.,Explanations for web relocation invoking optimal foraging require reliable differentiation between individual sites and overall habitat quality. We characterised natural conditions of resource variability over 20 days in artificial webs of the orb-web spider Gasteracantha fornicata to examine this requirement. 2.,Variability in catch success was high. Day-to-day catch success in 90% (18/20) catch sites fitted negative binomial distributions, whereas 10% fitted Poisson distributions. Considered across trap sites (overall habitat), variance in catch success increased proportionally faster than the mean (i.e. Taylor's Power Law, variance = 0.54mean1.764). 3.,We compared the confidence intervals for the expected cumulative catch in randomly drawn sequential samples from a frequency distribution representing the overall habitat (based on the parameters for Taylor's power law) and the frequency distribution of expected cumulative catch within each individual catch site [via randomisation based on the mean and negative binomial exponent (k)]. 4.,In all cases and across all sample sizes, median values for the power to differentiate habitat and catch sites never exceeded 0.2, suggesting that principles involved in optimal foraging, if operating, must be accompanied by a very high degree of uncertainty. 5.,Under conditions of high resource variability, many days must be spent in a single catch site if movement decisions are based on an ability to differentiate current catch site from overall habitat. Empirical evidence suggests this is never met. This may explain why proximal mechanisms that illicit quickly resolved behavioural responses have been more successful in describing web relocation patterns than those associated with optimal foraging. [source]


    Dispersion patterns of parasites in 0+ year three-spined sticklebacks: a cross population comparison

    JOURNAL OF FISH BIOLOGY, Issue 6 2002
    M. Kalbe
    Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes of c. 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of S.D. of each parasite species over all samples to form an ,individual parasitation index' (IPI), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks. [source]


    Designing Accurate Control Charts Based on the Geometric and Negative Binomial Distributions

    QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2005
    Neil C. Schwertman
    Abstract Attribute control charts are used effectively to monitor for process change. Their accuracy can be improved by judiciously selecting the sample size. The required sample sizes to achieve accuracy can be quite restrictive, especially when the nominal proportions of non-conforming units are quite small. The usual attribute control chart has a set sample size and the number of non-conforming units in the sample is plotted. If, instead of setting a specific sample size the number of non-conforming units is set, an alternative monitoring process is possible. Specifically, the cumulative count of conforming (CCC- r) control chart is a plot of the number of units that must be tested to find the rth non-conforming unit. These charts, based on the geometric and negative binomial distributions, are often suggested for monitoring very high quality processes. However, they can also be used very efficiently to monitor processes of lesser quality. This procedure has the potential to find process deterioration more quickly and efficiently. Xie et al. (Journal of Quality and Reliability Management 1999; 16(2):148,157) provided tables of control limits for CCC- r charts for but focused mainly on high-quality processes and the tables do not include any assessments of the risk of a false alarm or the reliability of detecting process change. In this paper, these tables are expanded for processes of lesser quality and include such assessments using the number of expected monitoring periods (average run lengths (ARLs)) to detect process change. Also included is an assessment of the risk of a false alarm, that is, a false indication of process deterioration. Such assessments were not included by Xie et al. but are essential for the quality engineer to make sound decisions. Furthermore, a hybrid of the control charts based on the binomial, geometric and negative binomial distributions is proposed to monitor for process change. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Statistical Inference in a Stochastic Epidemic SEIR Model with Control Intervention: Ebola as a Case Study

    BIOMETRICS, Issue 4 2006
    Phenyo E. Lekone
    Summary A stochastic discrete-time susceptible-exposed-infectious-recovered (SEIR) model for infectious diseases is developed with the aim of estimating parameters from daily incidence and mortality time series for an outbreak of Ebola in the Democratic Republic of Congo in 1995. The incidence time series exhibit many low integers as well as zero counts requiring an intrinsically stochastic modeling approach. In order to capture the stochastic nature of the transitions between the compartmental populations in such a model we specify appropriate conditional binomial distributions. In addition, a relatively simple temporally varying transmission rate function is introduced that allows for the effect of control interventions. We develop Markov chain Monte Carlo methods for inference that are used to explore the posterior distribution of the parameters. The algorithm is further extended to integrate numerically over state variables of the model, which are unobserved. This provides a realistic stochastic model that can be used by epidemiologists to study the dynamics of the disease and the effect of control interventions. [source]