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PubMed1985

Gastrointestinal nematode infections in wild ruminants Rupicapra rupicapra and Dama dama: influence of density and cohabitation with domestic ruminants.

The distribution of gastrointestinal nematodes in different populations of wild ruminants has been studied with regard to density of the animals and the presence of domestic ruminants in the habitat. The degree of parasite overdispersion among the hosts has been examined in the hypothesis of a negative binomial model of distribution. The results show that the density has a greater weight than cohabitation with domestic ruminants, in destabilizing the host-parasite relationship.

Animals↗
PubMed1996

[The psychophysics of sweet taste. 8. Interindividual variability of differential findings].

Contribution to the psychophysics of sweet taste. Part 8. On the inter-individual variability of the difference sensitivity. The variability of sensitivity of volunteers is a considerable imponderability for the comparison of sensoric results. The paper deals with the quantitative determination of the different sensitivity of sweet taste of 132 persons, 38 men and 94 women at the age of 19 to 64 years, using a statistically defined method. The numbers of errors are estimated for each person by means of one test difference of two saccharose concentrations using 10 pairs of comparisons and 4 runs. The average number of error of 10 comparisons corresponds to the individual measure of sensitivity. The medium value of the total distribution is 1.54 and the standard deviation is 1.19 errors. The value is only less above the binomial calculated number. In random test women show in comparison to men a significant higher variance at the statistical identical mean. A variance analysis based on the cutting of the distribution edges in the range of 0.5 to 4.0 errors can detect high significantly the steady learning effect of the volunteers during the runs. The method is applicable to determine classified subjective characteristics. The calculations of necessary group numbers for such experiments on the base of binomial distribution are discussed.

Adult↗
PubMed2005

Excluded volume effect for large and small solutes in water.

The cavitation effect, i.e., the process of the creation of a void of excluded volume in bulk solvent (a cavity), is considered. The cavitation free energy is treated in terms of the information theory (IT) approach [Hummer, G.; Garde, S.; Garcia, A. E.; Paulaitis, M. E.; Pratt, L. R. J. Phys. Chem. B 1998, 102, 10469]. The binomial cell model suggested earlier is applied as the IT default distribution p(m) for the number m of solute (water) particles occupying a cavity of given size and shape. In the present work, this model is extended to cover the entire range of cavity size between small ordinary molecular solutes and bulky biomolecular structures. The resulting distribution consists of two binomial peaks responsible for producing the free energy contributions, which are proportional respectively to the volume and to the surface area of a cavity. The surface peak dominates in the large cavity limit, when the two peaks are well separated. The volume effects become decisive in the opposite limit of small cavities, when the two peaks reduce to a single-peak distribution as considered in our earlier work. With a proper interpolation procedure connecting these two regimes, the MC simulation results for model spherical solutes with radii increasing up to R = 10 A [Huang, D. H.; Geissler, P. L.; Chandler, D. J. Phys. Chem. B 2001, 105, 6704] are well reproduced. The large cavity limit conforms to macroscopic properties of bulk water solvent, such as surface tension, isothermal compressibility and Tolman length. The computations are extended to include nonspherical solutes (hydrocarbons C1-C6).

Journal Article↗
PubMedDate not supplied

Predicting the distribution of aflatoxin test results from farmers' stock peanuts.

Suitability of the negative binomial function for use in estimating the distribution of sample aflatoxin test results associated with testing farmers' stock peanuts for aflatoxin was studied. A 900 kg portion of peanut pods was removed from each of 40 contaminated farmers' stock lots. The lots averaged about 4100 kg. Each 900 kg portion was divided into fifty 2.26 kg samples, fifty 4.21 kg samples, and fifty 6.91 kg samples. The aflatoxin in each sample was quantified by liquid chromatography. An observed distribution of sample aflatoxin test results consisted of 50 aflatoxin test results for each lot and each sample size. The mean aflatoxin concentration, m; the variance, S2 mean among the 50 sample aflatoxin test results; and the shape parameter, k, for the negative binomial function were determined for each of the 120 observed distributions (40 lots times 3 sample sizes). Regression analysis indicated the functional relationship between k and m to be k = 0.000006425m0.8047. The 120 observed distributions of sample aflatoxin test results were compared to the negative binomial function by using the Kolmogorov-Smirnov (KS) test. The null hypothesis that the true unknown distribution function was negative binomial was not rejected at the 5% significance level for 114 of the 120 distributions. The negative binomial function failed the KS test at a sample concentration of 0 ng/g in all 6 of the distributions where the negative binomial function was rejected. The negative binomial function always predicted a smaller percentage of samples testing 0 ng/g than was actually observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxins↗
PubMed1988

Analysis of finite mixture of distributions: a statistical tool for biological classification problems.

A microcomputer program to analyze finite mixtures of normal, binomial, Poisson or exponential distributions by a maximum likelihood estimation procedure is described. The program is coded in Turbo Pascal. Some theoretical and practical aspects of the compound distributions are discussed, mainly mathematical characteristics, fitting procedures and tests of hypotheses. The statistical tool, which is a cluster analysis technique, is presented in a general context for applications in biology. In particular an ecological example is briefly described: the age class structure resolution of a white-tailed deer population. To improve the usefulness for classification purposes, the link with discriminant analysis is examined. For a successful analysis of finite mixture of distributions the need for a large sample size is emphasized.

Age Factors↗
PubMed2003

A comparison of several regression models for analysing cost of CABG surgery.

Investigators in clinical research are often interested in determining the association between patient characteristics and cost of medical or surgical treatment. However, there is no uniformly agreed upon regression model with which to analyse cost data. The objective of the current study was to compare the performance of linear regression, linear regression with log-transformed cost, generalized linear models with Poisson, negative binomial and gamma distributions, median regression, and proportional hazards models for analysing costs in a cohort of patients undergoing CABG surgery. The study was performed on data comprising 1959 patients who underwent CABG surgery in Calgary, Alberta, between June 1994 and March 1998. Ten of 21 patient characteristics were significantly associated with cost of surgery in all seven models. Eight variables were not significantly associated with cost of surgery in all seven models. Using mean squared prediction error as a loss function, proportional hazards regression and the three generalized linear models were best able to predict cost in independent validation data. Using mean absolute error, linear regression with log-transformed cost, proportional hazards regression, and median regression to predict median cost, were best able to predict cost in independent validation data. Since the models demonstrated good consistency in identifying factors associated with increased cost of CABG surgery, any of the seven models can be used for identifying factors associated with increased cost of surgery. However, the magnitude of, and the interpretation of, the coefficients vary across models. Researchers are encouraged to consider a variety of candidate models, including those better known in the econometrics literature, rather than begin data analysis with one regression model selected a priori. The final choice of regression model should be made after a careful assessment of how best to assess predictive ability and should be tailored to the particular data in question.

Aged↗
PubMed1997

Time-frequency analysis of the first heart sound. Part 2: An appropriate time-frequency representation technique.

A simulated first heart sound (S1) signal is used to determine the best technique for analysing physiological S1 from the following five time-frequency representations (TFR): the spectrogram, time-varying autoregressive modelling, binomial reduced interference distribution, Bessel distribution and cone-kernel distribution (CKD). To provide information on the time and frequency resolutions of each TFR technique, the instantaneous frequency and the -3 dB bandwidth as functions of time were computed for each simulated component of the S1. The performance index for selecting the best technique was based on the relative error and the correlation coefficient of the instantaneous frequency function between the theoretical distribution and the computed TFR. This index served to select the best technique. The sensitivity of each technique to noise and to small variations of the signal parameters was also evaluated. The results of the comparative study show that, although important limitations were found for all five TFRs tested, the CKD appears to be the best technique for the time-frequency analysis of multicomponent signals such as the simulated S1.

Heart↗
PubMed1998

Chromosomal fragile site expression in lymphocytes from patients with schizophrenia.

Schizophrenia is a common complex mental disorder. The lifetime prevalence of this disease is about 1% across different populations. The etiology is still unknown despite decades of intensive study. This report is aimed at studying the relationship between chromosomal fragile sites and the etiology of schizophrenia. Lymphocytes of 72 schizophrenic patients and 66 healthy controls were cultured in M medium, which is deficient in folic acid, and in medium RPMI 1640 with distamycin A. G-banding was carried out on 100 metaphases of each individual. Fragile sites were characterized as specific chromosomal bands that exhibit nonrandom gaps or breaks. Culture in M medium resulted in significant differences in the total number of chromosomal lesions and the total number of cells with chromosomal lesions between patients and controls (P<0.001), while no difference was noted after exposure to distamycin A. In the case of M medium, 17 bands in both patients and controls were recognized as expressing fragile sites nonrandomly using a statistical method based on the relationship of the binomial and F distributions. Further analysis using Fisher's exact test revealed a significant excess of expression of a rare fragile site at 2q11.2 among patients compared with controls (P<0.05). In the case of distamycin A induction, 13 bands were identified as having nonrandom expression of fragile sites using the same statistical method. A significant excess expression of a fragile site at 9q12 was identified among patients compared with controls by applying Fisher's exact test (P<0.001). Thus, our data suggest that chromosomal bands 2q11.2 and 9q12 are interesting regions that may harbor important genes associated with schizophrenia.

Adult↗
PubMed1985

Spontaneous electrical activity induced by herpes virus infection in rat sensory neuron cultures.

Dissociated cultures of rat dorsal root ganglion neurons were infected with a syncytial strain of herpes simplex virus type 1. Over 90% of neurons in infected cultures were spontaneously active and fired action potentials which, on membrane potential hyperpolarization, were replaced by depolarizing events similar to excitatory postsynaptic potentials. Amplitude analysis of these events produced populations described by the sum of several unitary events with Gaussian rather than binomial or Poisson distributions. Such spontaneous activity was blocked by tetrodotoxin but not by low calcium high magnesium solutions containing cadmium. Simultaneous recording from pairs of spontaneously active neurons revealed excitatory connexions between cells. It is suggested that virus-induced fusion of nerve cell processes induces electrical coupling between sensory neurons, and that the resulting electrical network supports spontaneous activity.

Animals↗
PubMed2003

Oestrus ovis larval myiasis among goats in northern Jordan.

From December 1998 to December 1999, heads of 520 local goats slaughtered at the Irbid, Ramtha and Howarra Abattoirs (northern Jordan) were examined for the three larval instars (L(1)-L(3)) of Oestrus ovis. Of 520 heads, 126 (24%) were infested with O. ovis larvae. All three larval instars were observed in both sexes; all age groups were infested in each month of the year. The mean age of the goats sampled was 1.5 years. The numbers of parasites infesting hosts showed a significant (P<0.05) correlation with sheep age (r(sp)=0.31-0.42) for all three larval instars. The numbers of larvae in each host followed an overdispersed distribution, which fit a negative-binomial model (but not a Poisson distribution). There were more parasites recorded in the presence of purulent discharge or laryngitis, fewer in the presence of catarrhal discharge and no association with pharyngitis sinusitis, or rhinitis.

Abattoirs↗
PubMed2005

Dental procedures can be undertaken without alteration of oral anticoagulant regimen.

DATA SOURCES: Medline provided the primary data source with references from identified articles being reviewed for additional studies. The Cochrane Collaboration database was also searched and a search performed of cited references. STUDY SELECTION: Clinical studies, in English, examining perioperative management of patients receiving long-term oral anticoagulant (OAC) therapy were selected. DATA EXTRACTION AND SYNTHESIS: Data were extracted regarding management strategy, thrombo-embolic events and bleeding complications, and type of surgical or invasive procedure. Event rates were reported as number of patients experiencing the event divided by number of patients at risk. Binomial and Poisson distributions were used to calculate 95% confidence intervals (CI). RESULTS: A total of 31 reports were identified and concluded to be of generally poor quality. For studies reporting thrombo-embolic events, 29 events occurred in 1868 patients (1.6%; 95% CI, 1.0-2.1) of which seven were strokes (0.4%; 95% CI, 0.0-0.7). Major bleeding while receiving OAC was reported to be rare for dental procedures (occurring in four out of 2014 individuals), arthrocentesis (in none out of 32), cataract surgery (none out of 203), and upper endoscopy or colonoscopy with or without biopsy (no occurrences in 111 patients). For the other invasive and surgical procedures reviewed, OAC needs to be withheld and a suitable personalised perioperative management strategy instigated. A guideline, based on the limited evidence available, for the perioperative management of anticoagulation for procedures requiring discontinuation of OAC is presented. CONCLUSIONS: Certain surgical or invasive procedures can be undertaken in patients who are taking OAC therapy without alteration of their regimen. For procedures requiring discontinuation of OAC, personalised management strategies are required. More rigorous studies are needed to better inform this debate.

Comment↗
PubMed2004

Bias estimation in method comparison studies.

A test and a reference analytical method are usually compared for agreement based on paired data obtained from several independent subjects. Bias between two methods can be classified as constant and proportional. In this article, we provide an approach for maximum likelihood estimation of total bias between two methods and partitioning it into constant and proportional bias for each subject. Normal, binomial, or Poisson distribution are the conditional distributions of the response variable that we have considered here, whereas subjects are considered to be random sample from a normally distributed population. Real data on blood cell counts and hemoglobin are used for demonstration. The estimate of biases can be used to test different statistical hypotheses and/or for graphical interpretation of the agreement. The partitioning of total biases in terms of constant and proportional gives an insight on the sources of disagreement between two methods and helps designers and manufacturer's define a remedial strategy.

Algorithms↗
PubMed2004

Differences in characteristics of heroin inhalers and heroin injectors at admission to treatment: a preliminary study using a large database of client records.

AIMS: To compare the characteristics of heroin injectors vs. inhalers at their first admission to publicly funded treatment in Texas. METHODS: The sample consisted of 9732 unique clients who entered publicly funded treatment programs in Texas between 1997 and 2001 and who had a primary problem with either injected or inhaled heroin, which they had used in the past 30 days. The records were analyzed using a generalized linear model of logistic regression with the outcomes modeled as binomial and multinomial distribution and a hierarchical linear model for continuous outcomes to compare heroin inhalers and injectors. FINDINGS: There were large statistically significant differences between injectors and inhalers. Inhalers were more likely to be older at first use of heroin, to have entered treatment sooner, to have minor children at home, to have higher annual incomes, to be first admissions to treatment, and to have a secondary drug problem with crack cocaine. They were also more likely to be Hispanic [odds ratio (OR) = 1.74] or African-American (OR = 12.32). CONCLUSIONS: Even though the race/ethnic differences in the Texas population and the type of heroin available for use in Texas differs from that studied elsewhere, many of the characteristics of heroin users are similar. Inhalers have more strengths in many areas, and these findings raise the possibility that there are factors, particularly among African-American participants in Texas, that lessen the risk of injecting heroin. Efforts should be directed to providing therapeutic interventions to discourage the transition to injecting and to encourage inhalers to enter treatment earlier rather than progressing on to injecting. This analysis is the first part of a larger study of heroin users in public and private treatment.

Administration, Inhalation↗
PubMed1983

Frequency distribution of coliforms in water distribution systems.

Nine small water distribution systems were sampled intensively to determine the patterns of dispersion of coliforms. The frequency distributions of confirmed coliform counts were compatible with either the negative-binomial or the lognormal distribution. They were not compatible with either the Poisson or Poisson-plus-added zeroes distribution. The implications of the use of the lognormal distributional model were further evaluated because of its previous use in water quality studies. The geometric means from 14 data sets ranged from 10(-6) to 0.2 coliforms per 100 ml, and the geometric standard deviations were between 10 and 100, with one exception. If the lognormal model is representative of the coliform distribution; the arithmetic mean sample count is a poor estimator of the true mean coliform density, and the probability of water in a distribution system containing small patches with large coliform densities without detection by routine monitoring is finite. These conclusions have direct bearing on the interpretation of microbiological quality standards for drinking water.

Enterobacteriaceae↗
PubMed1999

Quality control in nucleic acid amplification methods: use of elementary probability theory.

Since it is not possible to state with certainty that contamination has occurred during a nucleic acid amplification assay in the absence of a positive result for a negative control, methods of elementary probability theory are used to illustrate how to identify those runs in which the possibility of contamination should be considered. The use of binomial and Poisson distributions and an analysis of clusters are presented with illustrative examples to demonstrate their use.

Artifacts↗
PubMed1993

A method for testing the nonrandomness of chromosomal breakpoints.

Testing the nonrandomness of breakage at a chromosome band is an essential step fo identifying a fragile site. In this paper, we propose a method derived by using the relationship between the binomial and F distributions for testing nonrandomness. The method is simple in calculation. It was applied to the detection of fragile sites for Chinese patients with colorectal carcinoma.

Carcinoma↗
PubMed2006

Modeling Sage data with a truncated gamma-Poisson model.

BACKGROUND: Serial Analysis of Gene Expressions (SAGE) produces gene expression measurements on a discrete scale, due to the finite number of molecules in the sample. This means that part of the variance in SAGE data should be understood as the sampling error in a binomial or Poisson distribution, whereas other variance sources, in particular biological variance, should be modeled using a continuous distribution function, i.e. a prior on the intensity of the Poisson distribution. One challenge is that such a model predicts a large number of genes with zero counts, which cannot be observed. RESULTS: We present a hierarchical Poisson model with a gamma prior and three different algorithms for estimating the parameters in the model. It turns out that the rate parameter in the gamma distribution can be estimated on the basis of a single SAGE library, whereas the estimate of the shape parameter becomes unstable. This means that the number of zero counts cannot be estimated reliably. When a bivariate model is applied to two SAGE libraries, however, the number of predicted zero counts becomes more stable and in approximate agreement with the number of transcripts observed across a large number of experiments. In all the libraries we analyzed there was a small population of very highly expressed tags, typically 1% of the tags, that could not be accounted for by the model. To handle those tags we chose to augment our model with a non-parametric component. We also show some results based on a log-normal distribution instead of the gamma distribution. CONCLUSION: By modeling SAGE data with a hierarchical Poisson model it is possible to separate the sampling variance from the variance in gene expression. If expression levels are reported at the gene level rather than at the tag level, genes mapped to multiple tags must be kept separate, since their expression levels show a different statistical behavior. A log-normal prior provided a better fit to our data than the gamma prior, but except for a small subpopulation of tags with very high counts, the two priors are similar.

Algorithms↗
PubMed2000

Misconceptions and false expectations in neutral evolution.

Neutral evolution results from random recurrent mutation and genetic drift. A small part of random evolution, that which is related to protein or DNA polymorphisms, is the subject of the Neutral Theory of Evolution. One of the foundations of this theory is the demonstration that the mutation rate (m) is equal to the substitution rate. Since both rates are independent of population size, they are independent of drift, which is dependent upon population size. Neutralists have erroneously equated the substitution rate with the fixation rate, despite the fact that they are antithetical conceptions. The neutralists then applied the random walk stochastic model to justify alleles or bases that were fixated or eliminated. In this model, once the allele or base frequencies reach the monomorphic states (values of 1.0 or 0.0), the absorbing barriers, they can no longer return to the polymorphic state. This operates in a pure mathematical model. If recurrent mutation occurs (as in biotic real systems) fixation and elimination are impossible. A population of bacteria in which m = 10(-8) base mutation (or substitution)/site/generation and the reproduction rate is 1000 cell cycle/year should replace all its genome bases in approximately 100,000 years. The expected situation for all sites is polymorphism for the four bases rather than monomorphism at 1.0 or 0.0 frequencies. If fixation and elimination of a base for more than 500,000 years are impossible, then most of the neutral theory is untenable. A new complete neutral model, which allows for recurrent substitutions, is proposed here based on recurrent mutation or substitution and drift alone. The model fits a binomial or Poisson distribution and not a geometric one, as does neutral theory.

Bacteria↗