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PubMed1996

The occurrence of ixodid ticks on wild mink Mustela vision in England and Wales.

Four species of ticks found to infest 1391 American mink (Mustela vison) in Britain in five years were, in declining order of frequency, Ixodes hexagonus, Ixodes canisuga, Ixodes ricinus and Ixodes acuminatus. Ixodes hexagonus and I. canisuga occurred on 40% and 2.5% of mink respectively. Infestation rates (the proportion of infested mink) of adult females, nymphs and larvae were similar and tended to be lower in summer. The distribution of infestation size (the number of ticks per host) for adult females describes a negative binomial. The mean infestation size of nymphs varied with the sex of the host was 5.2 for males and 4.2 for females. Mink are competent hosts for I.hexagonus.

Animals↗
PubMed2004

Impact of safety warnings on drug utilization: marketplace life span of cisapride and troglitazone.

STUDY OBJECTIVE: To evaluate the impact of safety alerts on the volume of cisapride and troglitazone usage. DESIGN: Retrospective database analysis. SETTING: University research center. MATERIAL: Idaho Medicaid claims data from January 1994--July 2000. MEASUREMENTS AND MAIN RESULTS: Monthly counts of total and new prescriptions filled for cisapride and troglitazone were analyzed graphically over time as a function of all prescriptions. New prescriptions were defined as those filled by patients who had not received the drug within the previous year. A binomial comparison of the 5 months before and after each safety alert was conducted by Poisson distribution. Overall and new cisapride usage increased after the first alert, which occurred in February 1995 (p<0.05). After the second alert, in September 1995, growth in new prescriptions ended but total prescriptions continued to grow (p<0.05). After the third alert, in June 1998, growth in total use ended and the number of new prescriptions declined (p<0.05). The final two alerts (June 1999 and January 2000) were met with significant declines (p<0.05 for both). Troglitazone was the subject of two alerts in October and December 1997. After these, overall usage increased (p<0.05), whereas the number o new prescriptions decreased (p<0.05). The third alert, in July 1998, caused no change as total prescription use continued to grow (p<0.05), whereas the number of new prescriptions decreased (p<0.05). A fourth alert, in June 1999, resulted in a decrease of overall usage and new prescriptions (p<0.05 for both). CONCLUSION: Numerous safety alerts were required for each drug before drug usage declined. The decline in overall use was slower than the decline in new prescriptions, possibly indicating a need for increased assessment of refilled prescriptions after the release of new safety data.

Chromans↗
PubMed1988

Estimation of allele frequencies at isoloci.

In some polyploid animals and plants, pairs of duplicated loci occur that share alleles encoding proteins with identical electrophoretic mobilities. Except in cases where these "isoloci" are known to be inherited tetrasomically, individual genotypes cannot be determined unambiguously, and there is no direct way to assign observed variation to a particular locus of the pair. For a pair of diallelic isoloci, nine genotypes are possible but only five phenotypes can be identified, corresponding to individuals with 0-4 doses of the variant allele. A maximum likelihood (ML) approach is used here to identify the set of allele frequencies (p, q) at the individual gene loci with the highest probability of producing the observed phenotypic distribution. A likelihood ratio test is used to generate the asymmetrical confidence intervals around ML estimates. Simulations indicate that the standard error of p is typically about twice the binomial sampling error associated with single locus allele frequency estimates. ML estimates can be used in standard indices of genetic diversity and differentiation and in goodness-of-fit tests of genetic hypotheses. The noncentral chi 2 distribution is used to evaluate the power of a test of apparent heterozygote deficiency that results from attributing all variation to one locus when both loci are polymorphic.

Alleles↗
PubMed2006

A chain-binomial model for intra-household spread of Mycobacterium tuberculosis in a low socio-economic setting in Pakistan.

A simulation study using Greenwood's chain-binomial model was carried out to elucidate the spread and control of Mycobacterium tuberculosis among the household contacts of infectious pulmonary tuberculosis (TB) patients. Based on the observed data, the maximum-likelihood estimates (+/-S.E.) of chain-binomial probabilities of intra-household M. tuberculosis transmission from an index case in 3-person and 4-person households were 0.313+/-0.008 and 0.325+/-0.009 respectively. The chi2 goodness-of-fit test of observed and simulated mean expected frequencies of cases revealed good fit for 3-person (P=0.979) and 4-person (P=0.546) households. With the assumption of varying risk of M. tuberculosis transmission across the households under beta-distribution, goodness-of-fit tests of observed and mean simulated expected frequencies revealed the inadequacy of Greenwood's chain-binomial model both for 3-person (P=0.0185) and 4-person (P<0.001) households. Simulated M. tuberculosis control strategy comprising efficient diagnosis, segregation and prompt antibiotic therapy of index pulmonary TB patients showed a substantial reduction of new cases among the household contacts in both household sizes. In conclusion, segregation coupled with prompt antibiotic therapy of the index case, chemoprophylaxis of M. tuberculosis-exposed household contacts, and the assessment of household environmental risks to devise and implement an educational programme may help reduce the TB burden in this and similar settings.

Family Characteristics↗
PubMed1992

On the use of historical control data to estimate dose response trends in quantal bioassay.

New tests for trend in proportions, in the presence of historical control data, are proposed. One such test is a simple score statistic based on a binomial likelihood for the "current" study and beta-binomial likelihoods for each historical control series. A closely related trend statistic based on estimating equations is also proposed. Trend statistics that allow overdispersed proportions in the current study are also developed, including a version of Tarone's (1982, Biometrics 38, 215-220) test that acknowledges sampling variation in the beta distribution parameters, and a trend statistic based on estimating equations. Each such trend test is evaluated with respect to size and power under both binomial and beta-binomial sampling conditions for the current study, and illustrations are provided.

Analysis of Variance↗
PubMed2005

Statistical analysis of efficacy in falls prevention trials.

BACKGROUND: Many different and sometimes inappropriate statistical techniques have been used to analyze the results of randomized controlled trials of falls prevention programs for elderly people. This makes comparison of the efficacy of particular interventions difficult. METHODS: We used raw data from two randomized controlled trials of a home exercise program to compare the number of falls in the exercise and control groups during the trials. We developed two different survival analysis models (Andersen-Gill and marginal Cox regression) and a negative binomial regression model for each trial. These techniques a) allow for the fact that falls are frequent, recurrent events with a non-normal distribution; b) adjust for the follow-up time of individual participants; and c) allow the addition of covariates. RESULTS: In one trial, the three different statistical techniques gave surprisingly similar results for the efficacy of the intervention but, in a second trial, underlying assumptions were violated for the two Cox regression models. Negative binomial regression models were easier to use. CONCLUSION: We recommend negative binomial regression models for evaluating the efficacy of falls prevention programs.

Accidental Falls↗
PubMed2000

Evidence for cooperativity between nicotinic acetylcholine receptors in patch clamp records.

It is often assumed that ion channels in cell membrane patches gate independently. However, in the present study nicotinic receptor patch clamp data obtained in cell-attached mode from embryonic chick myotubes suggest that the distribution of steady-state probabilities for conductance multiples arising from concurrent channel openings may not be binomial. In patches where up to four active channels were observed, the probabilities of two or more concurrent openings were greater than expected, suggesting positive cooperativity. For the case of two active channels, we extended the analysis by assuming that 1) individual receptors (not necessarily identical) could be modeled by a five-state (three closed and two open) continuous-time Markov process with equal agonist binding affinity at two recognition sites, and 2) cooperativity between channels could occur through instantaneous changes in specific transition rates in one channel following a change in conductance state of the neighboring channel. This allowed calculation of open and closed sojourn time density functions for either channel conditional on the neighboring channel being open or closed. Simulation studies of two channel systems, with channels being either independent or cooperative, nonidentical or identical, supported the discriminatory power of the optimization algorithm. The experimental results suggested that individual acetylcholine receptors were kinetically identical and that the open state of one channel increased the probability of opening of its neighbor.

Animals↗
PubMed1982

Transmission of Schistosoma mansoni from man to snail: laboratory studies on the influence of snail and miracidial densities on transmission success.

The relationship between infection success, the density of Schistosoma mansoni miracidia and the density of the snail host Biomphalaria glabrata was examined experimentally. Within laboratory infection arenas, the distribution of miracidial infections/snail was approximately uniform and the net rate of snail infection was directly positive binomial to miracidial density. In contrast, however, the rate of infection declined exponentially as snail density increased. Mathematical models are developed to aid in the estimation of infection rates and experimental results are discussed in the context of the transmission dynamics of schistosomiasis.

Animals↗
PubMed1989

Neuropsychological function in physically asymptomatic, HIV-seropositive men.

Twenty asymptomatic, HIV-seropositive homosexual men and a control group of 20 seronegative homosexual men were evaluated for evidence of neuropsychological impairment. Two-tailed paired t-tests of group differences revealed that the seropositive patients had significantly lower scores on two of 20 neuropsychological measures. Ten seropositive patients had scores two standard deviations below the sample, compared with three seronegative patients, a significantly different distribution (p = .04). The HIV-infected group exhibited lower mean scores on 17 of 20 variables (binomial probability, p less than .005). The 10 seropositive patients with scores that fell below the cut-off had significantly lower mean T4/T8 ratios than the 10 seropositive patients with scores above the cut-off (p = .02). The data suggest that a subpopulation of HIV-infected adults may exhibit subtle neuropsychological impairment before they develop clinical signs of cognitive deficit or immunosuppression.

AIDS Dementia Complex↗
PubMed1997

Restrictive clonal allocation in the chimeric mouse brain.

Whether, and to what extent, lineage restriction contributes to the organization of the mammalian brain remains unclear. Here we address this issue by examining the distribution of clonally related cells in chimeric mice generated by injecting genetically tagged embryonic stem (ES) cells into blastocyst embryos. Our examination of postnatal chimeric brains revealed that the vast majority of labeled ES cell descendents were confined within a different subset of brain regions in each animal. Moreover, the deployment of labeled cells in different brain regions was distinctive. The pattern of ordered and binomial colonization suggested that early diversified founder cells may constrain the fates of their descendants through a restriction of dispersion. In addition, the symmetrical distribution of ES cell descendants suggests that bilaterally corresponding structures may arise from a common set of progenitor cells. Finally, clones of cells formed a continuous band within the deep strata of the neocortex. This later finding in conjunction with the radial distribution of clones in remaining layers observed in previous studies indicates that the cerebral neocortex may derive from two groups of founder cells, which is consistent with the hypothesis of dual phylogenetic origins of the mammalian cerebral cortex.

Animals↗
PubMed2000

Zero-inflated Poisson and binomial regression with random effects: a case study.

In a 1992 Technometrics paper, Lambert (1992, 34, 1-14) described zero-inflated Poisson (ZIP) regression, a class of models for count data with excess zeros. In a ZIP model, a count response variable is assumed to be distributed as a mixture of a Poisson(lambda) distribution and a distribution with point mass of one at zero, with mixing probability p. Both p and lambda are allowed to depend on covariates through canonical link generalized linear models. In this paper, we adapt Lambert's methodology to an upper bounded count situation, thereby obtaining a zero-inflated binomial (ZIB) model. In addition, we add to the flexibility of these fixed effects models by incorporating random effects so that, e.g., the within-subject correlation and between-subject heterogeneity typical of repeated measures data can be accommodated. We motivate, develop, and illustrate the methods described here with an example from horticulture, where both upper bounded count (binomial-type) and unbounded count (Poisson-type) data with excess zeros were collected in a repeated measures designed experiment.

Animals↗
PubMed1975

Statistical inferences about injury and persistence of environmentally stressed bacteria.

A standard technique for ascertaining the survival characteristics of bacteria after being environmentally stressed is to incubate the bacteria on both selective and non-selective media and count the colonies produced. Based on these colony counts, indexes of injury and persistence of the bacteria are calculated. To compare the stress of two different environments, a persistence ratio is calculated. In this paper, methods of statistical inference concerning these indexes and ratios are presented. These statistical methods use well-known procedures for analysis of binomial data and 2 times 2 table data, and are appropriate when the colony counts follow a Possion distribution.

Bacteria↗
PubMed1973

Changes in the statistics of transmitter release during facilitation.

1. The statistical nature of transmitter release during facilitation was studied at single synaptic sites by recording extracellular excitatory junctional potentials from the claw opener muscle in crayfish.2. At low temperatures, single quanta could be counted in the responses to nerve impulses. The distribution of the number of quanta observed (x) was most accurately described by assuming that x is a binomial random variable.3. A quantitative estimate was made of the effects of errors in counting quanta due to the simultaneous release of quanta and the release of quanta which were not individually detectable above the noise of the recording system. Such errors of observation cannot account for the deviation of quantal release from a Poisson distribution.4. Facilitated release occurred in the responses to the second of two closely following nerve impulses and in the responses to successive impulses in a tetanus. In both cases, the increase in the average number of quanta released (m) could be attributed entirely to an increase in the probability (p) that available quanta were released.5. The results can be interpreted most easily in terms of a model in which the maximum number of releasable quanta is limited by a finite number of discrete release sites within recording distance of the microelectrode. In this model, the binomial parameter n is an estimate of the number of these sites, and the statistical parameter p is a compound probability depending on the rate of re-occupying sites after a nerve discharge and the probability that an impulse activates an occupied site.

Animals↗
PubMed2006

Incarceration as forced migration: effects on selected community health outcomes.

OBJECTIVES: We estimated the effects of high incarceration rates on rates of sexually transmitted infections and teenage pregnancies. METHODS: We calculated correlations between rates of incarceration in state prisons and county jails and rates of sexually transmitted infections and teenage pregnancies for each of the 100 counties in North Carolina during 1995 to 2002. We also estimated increases in negative health outcomes associated with increases in incarceration rates using negative binomial regression analyses. RESULTS: Rates of sexually transmitted infections and teenage pregnancies, adjusted for age, race, and poverty distributions by county, consistently increased with increasing incarceration rates. In the most extreme case, teenage pregnancies exhibited an increase of 71.61 per 100000 population (95% confidence interval [CI]=41.88, 101.35) in 1996 after an increase in the prison population rate from 223.31 to 468.58 per 100000 population in 1995. CONCLUSIONS: High rates of incarceration can have the unintended consequence of destabilizing communities and contributing to adverse health outcomes.

Adolescent↗
PubMed2005

Reforming health care: evidence from quantile regressions for counts.

I consider the problem of estimating the effect of a health care reform on the frequency of individual doctor visits when the reform effect is potentially different in different parts of the outcome distribution. Quantile regression is a powerful method for studying such heterogeneous treatment effects. Only recently has this method been extended to situations where the dependent variable is a (non-negative integer) count. An analysis of a 1997 health care reform in Germany shows that lower quantiles, such as the first quartile, fell by substantially larger amounts than what would have been predicted based on Poisson or negative binomial models.

Adult↗
PubMed1983

The prevalence and intensity of Ascaris lumbricoides infections in Moslem children from northern Bangladesh.

The results are presented of a horizontal epidemiological survey of intestinal infections of children aged between six months and 15 years in three adjacent villages in northern Bangladesh. On the basis of 203 stool sample examinations, the prevalence of Ascaris lumbricoides, Trichuris trichiura, hookworm and amoebic infections was estimated as 68, 56, 53 and 19%, respectively. Age-specific prevalence data indicated that approximately 90% of the children were harbouring patent Ascaris infections by the time they were four years old and there was some evidence to suggest differences in the pattern of age-prevalence between male and female children. The intensity of Ascaris infection was found to rise to its maximum value within the first four years of life. No significant differences were detected in the mean worm burdens of children aged between four and 15 years. Each child in this age-group harboured on average 10 worms. The frequency distribution of numbers of A. lumbricoides per host was found to be overdispersed, with a value of the negative binomial parameter, k, of 0.44. The degree of aggregation was found to be approximately the same for each age-class of the population between one and 15 years (0.26 less than or equal to k less than or equal to 0.82). No evidence was found to suggest a density-dependent reduction in the weight of either male or female Ascaris within the range one to 43 worms per host.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2007

The role of the phosphoinositides at the Golgi complex.

Eukaryotic cells are organized into a complex system of subcompartments, each with its distinct protein and lipid composition. A continuous flux of membranes crosses these compartments, and in some cases direct connections exist between the different organelles. It is thus surprising that they can maintain their individual identities. Small GTPases and the phosphoinositides have emerged as the key regulators in the maintenance of the identity of the Golgi complex. This property is due to their ability to act either alone or, more often, in combination, as cues directing and controlling the recruitment of proteins that possess phosphoinositide-binding domains. Among these many proteins there are the lipid transfer proteins, which can transfer ceramide, oxysterol, cholesterol and possibly glucosylceramide. By regulating these lipid transfer proteins in this way, this binomial combination of the small GTPases and the phosphoinositides acquires a further important role: control of the synthesis and/or distribution of other important integral constituents of cell organelles, such as the sphingolipids and cholesterol. This role is particularly relevant at the level of the Golgi complex, a key organelle in the biosynthesis, transport and sorting of both lipids and proteins that is located at the intersection of the secretory and endocytic pathways.

1-Phosphatidylinositol 4-Kinase↗
PubMed1977

Citrate synthase activity in human skeletal muscle.

Citrate synthase activity in soluble human muscle extracts (KCl-containing triethanolamine buffer) amounts to 17.5+/-6.97 U/g wet weight at 37 degrees C (n=36 healthy male subjects). Double determinations, both using two procedures and with muscle samples divided into two pieces and analyzed separately, gave very good reproducibilities. The possible causes of the comparatively high values are discussed. Significant correlations of citrate synthase activity with NADP-linked isocitrate dehydrogenase (r=+0.826) and hexose phosphate isomerase (r=-0.582) were found. The distribution of citrate synthase activity in the samples studied is not of the normal type but appears to be binomial.

Adolescent↗