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PubMed1985

Epidemiology of subperiodic bancroftian filariasis in Samoa 8 years after control by mass treatment with diethylcarbamazine.

In 1979, a microfilarial prevalence study was conducted in a population of 8385 persons inhabiting 28 villages in Samoa using both the nuclepore filtration (NP) method (with 1 ml blood) and the fingerprick (FP) method (with 60 mm(3) blood). The overall prevalence rate was 4.5% by the NP method and 3.8% by the FP method. The average microfilarial prevalence in males was 2.3 times higher than in females, and the rate among males aged 30 years and over was as high as 20%. The positive cases were found to be concentrated in certain households.The median microfilarial density (MfD-50) for the whole of Samoa was 18.6 using 60-mm(3) blood samples (males, 21.4; females 14.2). While the MfD-50 of any village has a positive association with the microfilarial prevalence rate of that village, a relatively high MfD-50 was noticed among young people under 20 years of age together with low prevalence rates.The negative binomial distribution was fitted to the data on the distribution of microfilarial counts in Samoa and gave a better fit than the log-normal distribution. The data having been fitted to the negative binomial, the number of false negatives could be determined as 9% of the estimated number of positives in the survey population when the NP method was employed and about 25% with the FP method.Further studies revealed that 15.1% of the microfilaria carriers presented some clinical manifestation, the most common being an attack of filarial fever (13.1%). The average duration of a fever attack was 3.5 days and the total period with fever/person/year averaged 27.1 days.

Adolescent↗
PubMed2000

Age and seasonal variations in the prevalence of Oestrus ovis larvae among sheep in northern Jordan.

During the period March 1996-July 1997, 417 heads of Awassi sheep slaughtered at the Irbid Abattoir (northern Jordan) were examined for the three larval instars (L1, L2 and L3) of Oestrus ovis. Of the 417 heads, 242 (58%) were infested with O. ovis larvae. Larval numbers were highly aggregated. The lowest number of larvae and the lower quartile were both zero, whilst the median was two and the upper quartile was 12. The highest number of larvae recovered from one head was 151. All three larval instars were observed in each month of the year. July and October had the highest proportions of L1, 75 and 78%, respectively, among infected animals (adjusted for age). The number of larvae increased with age. Infestation with live larvae was associated with inflammatory responses in the upper respiratory tract and with catarrhal or purulent discharge. The percentage of infested sheep and the mean monthly total number of larvae/sheep peaked in the warmer part of the year. Most larvae were L1 except during the spring when L2 and L3 predominated. Distribution analysis demonstrates that the numbers of larvae recovered in the sheep population followed a negative-binomial distribution. Furthermore, the negative-binomial constant k for each month correlated with the monthly prevalence.

Abattoirs↗
PubMed1999

Biological dosimetry of chernobyl cleanup workers: inclusion of data on age and smoking provides improved radiation dose estimates.

We report the results of a study of chromosome translocations in 126 Russian subjects who participated in the cleanup activities at Chernobyl and another 53 subjects, from other places in Russia, who were not exposed at Chernobyl. In agreement with our earlier study, we find increased translocation frequencies among the exposed compared to Russian controls. We describe statistical methods for estimating the dose of ionizing radiation determined by scoring chromosome translocations found in circulating lymphocytes sampled several years after exposure. Two statistical models were fitted to the data. One model assumed that translocation frequencies followed an overdispersed Poisson distribution. The second model assumed that translocation frequencies followed a negative binomial distribution. In addition, the effects of radiation exposure were modeled as additive or as multiplicative to the effects of age and smoking history. We found that the negative binomial model fit the data better than the overdispersed Poisson model. We could not distinguish between the additive and the multiplicative model with our data. Individual dose estimates ranged from 0 (for 43 subjects) to 0.56 Gy (mean 0.14 Gy) under the multiplicative model and from 0 to 0.95 Gy (mean 0.15 Gy) under the additive model. Dose estimates were similar under the two models when the number of translocations was less than 4 per 100 cells. The additive model tended to estimate larger doses when the number of translocations was greater than 4 per 100 cells. We also describe a method for estimating upper 95% tolerance bounds for numbers of translocations in unexposed individuals. We found that inclusion of data on age and smoking history was important for dose estimation. Ignoring these factors could result in gross overestimation of exposures, particularly in older subjects who smoke.

Adult↗
PubMed2005

A shared response model for clustered binary data in developmental toxicity studies.

Existing distributions for modeling fetal response data in developmental toxicology such as the beta-binomial distribution have a tendency of inflating the probability of no malformed fetuses, and hence understating the risk of having at least one malformed fetus within a litter. As opposed to a shared probability extra-binomial model, we advocate a shared response model that allows a random number of fetuses within the same litter to share a common response. An explicit formula is given for the probability function and graphical plots suggest that it does not suffer from the problem of assigning too much probability to the event of no malformed fetuses. The EM algorithm can be used to estimate the model parameters. Results of a simulation study show that the EM estimates are nearly unbiased and the associated confidence intervals based on the usual standard error estimates have coverage close to the nominal level. Simulation results also suggest that the shared response model estimates of the marginal malformation probabilities are robust to misspecification of the distributional form, but not so for the estimates of intralitter correlation and the litter-level probability of having at least one malformed fetus. The proposed model is fitted to a set of data from the U.S. National Toxicology Program. For the same dose-response relationship, the fit based on the shared response distribution is superior to that based on the beta-binomial, and comparable to that based on the recently proposed q-power distribution (Kuk, 2004, Applied Statistics53, 369-386). An advantage of the shared response model over the q-power distribution is that it is more interpretable and can be extended more easily to the multivariate case. To illustrate this, a bivariate shared response model is fitted to fetal response data involving visceral and skeletal malformation.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed2001

Stability of psychometric questionnaires.

In 1999, Wilson and Batterham proposed a new approach to assessing the test-retest stability of psychometric questionnaires. They recommended assessing the proportion of agreement - that is, the proportion of participants that record the same response to an item - using a test-retest design. They went on to use a bootstrapping technique to estimate the uncertainty of the proportion of agreement. The aims of this short communication are (1) to demonstrate that the sampling distribution of the proportion of agreement is well known (the binomial distribution), making the technique of 'bootstrapping' redundant, and (2) to suggest a much simpler, more sensitive method of assessing the stability of a psychometric questionnaire, based on the test-retest differences (within-individuals) for each item. Adopting methods similar to Wilson and Batterham, 97 sport students completed the Social Physique Anxiety Scale on two occasions. Test-retest differences were calculated for each item. Our results show that the proportion of agreement ignores the nature of disagreement. Items 4 and 11 showed similar agreement (44.3% and 43.3% respectively), but 89 of the participants (91.8%) differed by just +/-1 point when responding to item 4, indicating a relatively stable item. In contrast, only 78 of the participants (80.4%) recorded a difference within +/- 1 point when responding to item 11, suggesting quite contrasting stability for the two items. We recommend that, when assessing the stability of self-report questionnaires using a 5-point scale, most participants (90%) should record test-retest differences within a reference value of +/- 1.

Adult↗
PubMed1998

[Esophageal carcinoma in part of population of Yangquan City].

OBJECTIVE: To evaluate the contribution of genetic factors to the occurrence of esophageal carcinoma (EC). METHODS: A genetic epidemiology survey of one-tenth of the whole population (130,000 people) was conducted in 6 towns of Yangquan City, Shanxi province in 1994. 228 high-risk (EC) families were matched with equal number of control families. RESULTS: The heritability of EC among first grade blood relatives was 52.6%, that among second grade blood relatives was 31.2%, and the summing up powered heritability was 49.2%. the segregation ratio was 18 +/- 3%, far less than 25%, suggesting a multi-gene effect. The distribution of EC in families did not fit well the binomial distribution, suggesting familial aggregation. The relative risk among male first grade blood relatives was 10.49, female was 7.69, in sum was 9.17. The attributive risks (AR) among first grade blood relatives were 62.13/100,000(male), 99.14/100,000(female) and 75.15/100,000(total). All of these figures were higher than the average (40.17/100,000). CONCLUSION: Genetic factors plays important roles in occurrence of EC in the Taihang mountain region.

Aged↗
PubMed2003

[Application of capture-recapture method on injury control].

OBJECTIVE: To explore relationships among several capture-recapture methods to be used in injury studies. METHODS: Comparing the method on the estimation number of missed cases with supergeometric distribution and proportional methods and study the relationship between the three methods. RESULTS: Results from estimation method for number of missed cases and supergeometric distribution were identical while the formula of estimation method for number of missed cases could be induced from one of supergeometric distribution formula. The distribution of injured population did not belong to the negative binomial distribution. The estimation range was not the same between proportional method and supergeometric distribution. CONCLUSIONS: Either supergeometric distribution or estimation method for number of missed cases could be chosen, but the former was simple in calculation. Considering the estimating range was not the same between supergeometric distribution and proportional method, conditions for application must be considered during implementation.

Epidemiologic Methods↗
PubMed1992

Probability models of the rate of infection with tick-borne encephalitis virus in Ixodes persulcatus ticks.

A total of 3,254 adults of Ixodes persulcatus tick were collected in a taiga forest habitat situated in the Amgun river basin (Khabarovsk region, the Far East, USSR) and examined individually for the presence and amount of tick-borne encephalitis virus. The over-all proportion of infected ticks was 6.6% and it varied between 3.4% and 9.4% in the years 1982 to 1985. The amount of virus per tick was approximated by the gamma distribution determining a probability that the number of plaque-forming units (PFU) per tick is not greater than a selected value. The frequency distribution of infected ticks followed a model of the negative binomial distribution, enabling the estimation of probability of the occurrence of a given number of infected ticks in the area. However, the parameters of both probability models (i.e., the PFU content per tick, and the frequency of infected ticks) varied for particular years.

Animals↗
PubMed1990

Estimation of absolute numbers of damselfly nymphs (Odonata: Coenagrionidae) by dipper sampling in California rice fields with seasonal, spatial distributions and vegetation association.

Estimates of relative and absolute density in rice field populations of damselfly nymphs (predominantly Enallagma civile with few Ischnura denticollis) were compared using the regression method. An equation, X = Y divided by 0.0016, allows estimation of absolute density (X) from a relative density index (Y, dipper count). In the rice growing area of Fresno, California, nymphal population peaks appeared during June and August approaching 3-5 million per 0.405 ha (1 acre). Spatial distribution was theoretically represented fairly well by a negative-binomial distribution. The degree of clumping is one of overdispersed types; it is especially classified as a model of randomly distributed colonies with mean colony size fixed. Presence or absence of submerged vegetation markedly affected damselfly nymphal density but the biomass of submerged or emerged vegetation was not a significant factor.

Animals↗
PubMed1988

The induction of chromosome aberrations during the course of radiation therapy for morbus Hodgkin.

In a patient with Morbus Hodgkin, structural aberrations of the chromosome type in peripheral lymphocytes were analyzed during radiation therapy (accumulated target dose 44.6 Gy: 22 fractions of 1.8 Gy each and 2 fractions of 2.5 Gy each at the end of the therapy). The blood was sampled about 5 min after a fraction and/or 24, 48, or 72 h thereafter. The frequency of dicentric chromosomes:acentric fragments:centric ring chromosomes is 37:14:1 throughout the therapy. Independent of the time of blood sampling after a fraction, the distributions of dicentrics and acentrics are overdisperse and represent negative binomial distributions. The yields from these aberrations, as determined during the course of radiotherapy, are best fitted to a linear-quadratic function with a negative quadratic term. The two dose-effect curves (blood sampling about 5 min and 24 to 72 h after a fraction) of dicentrics and acentrics do not differ significantly. Up to an accumulated target dose of about 20 Gy the percentages of cells with chromosome aberrations increase to about 48 to 65% and, at this level, remain constant until the end of therapy.

Adult↗
PubMed1999

Process control procedures to augment quality control of leukocyte-reduced red cell blood products.

Quality control of leukocyte-reduced packed red cell units (LRprc) produced in blood facilities must conform to regulatory criteria, which state that units may not contain more than 1 x 10(6) to 5 x 10(6) white blood cells (WBC) per unit. The post-filtration WBC content of a total of n = 386 LRprc units was counted with a Nageotte chamber to model the probability that a unit would not meet the regulatory criteria. The distribution of the residual leukocyte counts is close to a negative binomial distribution (NBD) and is independent of the packed red cell volume filtered. The observed probability that a unit of blood has a residual WBC greater than 5 x 10(6) is 2.6 +/- 2.6 x 10(-3). A power analysis of the two-sample Kolmogorov-Smirnov (KS) test in this application shows that a sample size of 20 is sufficient for determining that the process is in control when an out of control process has a k NBD parameter greater than or equal to that of the in control process. The three out of control processes observed to date appear to have this property. A sample of size 80 may be necessary for confirming that process validation data sets conform to the larger 'reference' database (n = 386) for processes that are out of control in such a way that their k NBD parameter is less than the k parameter of the in control process.

Blood Component Removal↗
PubMed2005

Mediterranean Diplodus annularis (Teleostei: Sparidae) and its brain parasite: unforeseen outcome.

Patterns of parasite load and aggregation of the bird trematode Cardiocephaloides longicollis in its main intermediate host in the Mediterranean, the annular sea bream, Diplodus annularis, were studied in a large sample collected off Valencia (Spain) and are discussed within the context of the parasite induced host mortality hypothesis. The metacercariae were located within large composite cysts of host origin in the ventricles of the optic lobes of the cerebrum. A weak immunological response was detected in older fish, which was significantly associated with the total parasite load. Although the mean abundance of C. longicollis showed a tendency to increase with host size, the infection levels were generally homogeneous with a noticeable plateauing in the intermediate size classes. The distribution of the metacercariae was aggregated and agreed with the negative binomial distribution. There was a marked decline in parasite aggregation in the largest size-class, suggesting parasite-induced host mortality in the oldest fish possibly due to predation by large non-host fish predators. On the other hand, levelling off of abundance and decrease in heterogeneity of parasite distribution within the intermediate age cohort could indicate that these sizes are being rapidly and/or constantly removed from the host population due to by-catch fishing. The overall high infection levels and the continuous recruitment across age cohorts provides evidence that an enhanced parasite transmission is taking place in the Gulf of Valencia due to increased spatial overlap of the hosts involved in the life cycle. We suggest a human-induced facilitation of the digenean life cycle due to the fact that gulls in the area feed extensively on discards, thus indicating the possibility of an unforeseen effect of fishing practices in a marine littoral system.

Animals↗
PubMed1989

Adenosine triphosphate utilization rates and metabolic pool sizes in intact cells measured by transfer of 18O from water.

The hydrolytic rates and metabolic pool sizes of ATP were determined in intact cells by monitoring the time courses of 18O incorporation from 18O-water into the gamma-phosphoryl of ATP and orthophosphate. To calculate the rate of ATP hydrolysis, a kinetic model is used to fit the time course of the 18O labeling. The size of the metabolic pool of ATP is calculated from the 18O distribution after isotopic equilibrium has been achieved. Metabolic pools have a binomial distribution of 18O whereas nonmetabolic pools exhibit negligible 18O labeling. The application and limitations of this approach are illustrated with data from isolated toad retinas and human platelets. At 22 degrees C, the time constant of ATP hydrolysis in the dark-adapted toad retina is about 30 s. Under these conditions, over 80% of the retinal ATP is involved in high-energy phosphate metabolism. It is calculated that when cGMP metabolic flux in the photoreceptors is maximally stimulated by light, it accounts for 10% of the ATP utilization by the entire retina. The time constant of ATP hydrolysis in human platelets at 37 degrees C is approximately 1 s, and 60% of the platelet ATP is involved in energy metabolism.

Adenosine Diphosphate↗
PubMed1984

Serologic evidence for widespread infection with La Crosse and St. Louis encephalitis viruses in the Indiana human population.

The vast under-reporting of La Crosse virus and St. Louis encephalitis virus infections in Indiana residents was evident when numerous inapparent infections were detected retrospectively using serum dilution neutralization analyses of serum obtained in November 1978-April 1979 from 10,208 persons (0.2% of the state's population). An antibody prevalence rate of 3.6% to St. Louis encephalitis virus was detected in the sample population as a whole, with rates as high as 13.2% for residents of individual counties. The estimated average annual rate of infection for the whole population was 0.32%. The antibody prevalence to La Crosse virus in the sample population as a whole was 2.3%, with rates ranging up to 12.5% for residents of individual counties. The estimated average annual rate of infection for the whole population was 0.29%. The epidemiologic behavior of the two viruses was quite different. Age-specific antibody prevalence for St. Louis encephalitis virus indicated a pattern of endemic infection existed in the population as a whole; antibody prevalence rose as the population aged. However, many other infections apparently occurred during the 1975 and earlier epidemics. Age-specific antibody prevalence for La Crosse virus indicated a typical pattern of endemic infection was present. The antibody prevalence to La Crosse virus was best described by the Poisson distribution and that of St. Louis encephalitis virus by the negative binomial distribution. These data support the hypothesis that St. Louis encephalitis virus primarily produces intermittent epidemics in the Midwest while La Crosse virus produces continuous seasonal endemic infections. However, evidence suggestive of a low level of interepidemic St. Louis encephalitis virus infection in the population was also obtained. Computer-drawn synagraphic mapping view "maps" of regional antibody prevalence rates demonstrated the existence of distinct foci of infection for each virus in the human population.

Adolescent↗
PubMed1998

Compositional heterogeneity within, and uniformity between, DNA sequences of yeast chromosomes.

The heterogeneity within, and similarities between, yeast chromosomes are studied. For the former, we show by the size distribution of domains, coding density, size distribution of open reading frames, spatial power spectra, and deviation from binomial distribution for C + G% in large moving windows that there is a strong deviation of the yeast sequences from random sequences. For the latter, not only do we graphically illustrate the similarity for the above mentioned statistics, but we also carry out a rigorous analysis of variance (ANOVA) test. The hypothesis that all yeast chromosomes are similar cannot be rejected by this test. We examine the two possible explanations of this interchromosomal uniformity: a common origin, such as genome-wide duplication (polyploidization), and a concerted evolutionary process.

Analysis of Variance↗
PubMed1990

Monitoring of genotoxic exposure of humans by the sister chromatid exchange test. Methodology and confounding factors.

During the last decades several in vitro assays for measurement of genotoxic exposure have been developed. Exposure of humans to genotoxic products in their workplaces and the environment may be evaluated by means of the sister chromatid exchange test (SCE), which visualize exchange of DNA material between sister chromatids of a chromosome. This thesis deals with the development of SCE methodology and screening of confounding factors to make the method useful in population monitoring of genotoxic exposure of chemicals in vivo. Human lymphocytes are cultured under standardized conditions. The cells are prepared for chromosome analysis by means of new-developed apparatuses treating 12 samples simultaneously. By this method the preparation is speeded up and breathing of glacial acetic acid is minimized. Slides are prepared and stained. The staining procedure includes irradiation of the slides with long wave UV light. The light source has been optimized with regard to simplicity and spectral distribution to fit the absorption spectrum of the dye bisbenzimid. The irradiation time and dose to produce distinct harlequin stained chromosomes has been found. Population screening demands analysis in microscope of a great number of chromosomes. The working time at microscope is long and improvement of ergonomics and automation to speed up the procedure was obtained by development of a special microscope which projects the picture of SCEs at table level. The scanning table was motorized. These changes gave excellent ergonomic proporties as fixed positions of the eyes and hands were avoided. The system is fast and flexible and may semiautomatically produce karyotypes. By pointing out SCEs the system automatically registers SCE number, cell coordinates, mitosis quality and perform statistics. The statistical model which best describe the distributions of SCE data has been analysed. This was a negative binomial distribution, which is close to the Poisson distribution. The transformation y = (S).5 + (S + 1).5 follows a normal distribution. Variances of the transformation of the sum of SCEs in 30 cells within subjects and between subjects have been calculated, and on that basis the demands to sample size have been calculated. To avoid to make false statements about a connection between an exposure and SCE a detailed knowledge of confounding factors is essential. Of endogenous factors gender, age, race, and heredity have been considered. Of these gender and age contribute to the variation in SCE. Very high SCE level has been found in healthy members of a family and such cases have to be excluded from exposure studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Basic regulatory parameters of the host-parasite system for warble flies of farm animals using Hypoderma bovis as an example.

While studying the consistent patterns in the host-parasite relationships on the model of warble flies infesting cattle, a firm internal regulatory system governing the number of parasites on the host and reflected in the level of populations, has been demonstrated. This regulatory system is governed by mathematical-statistical laws and therefore can be modelled and its different features expressed mathematically. The distribution of parasites in the host population agrees with the negative binomial distribution. Main mathematical formulations of the regulatory system (parameters) and defensive responses of the host to the invasion of parasites are analyzed. From the above consistent patterns important conclusions are drawn for the control of cattle hypodermatosis in practice. The mathematical model elucidates two states of control--the first stage conforms to the natural regulatory system leading to a marked decrease of the degree of infestation, and the second stage is aiming at the eradication of the disease. It may be deduced from the above said that the control of hypodermatosis is expedient primarily in juvenile cattle, as shown by the results of the control carried out in Czechoslovakia.

Animals↗
PubMed1983

Fibrous intimal thickening and atheronecrosis of the thoracic aorta. Some background for mathematical theory.

Paraffin sections from the lateral walls of the thoracic aorta, stained with a nigrosin-Gomori trichrome combination, were used to separate subjects into those having (Yes-A) and not having (No-A) atheronecrosis, as operationally defined. In 174 of the 211 No-A subjects, the dispersal of fibrous intimal thickening (FIT) over a carefully selected set of loci was fitted well (goodness of fit p greater than 0.05) by the negative binomial distribution. In 99 of the 125 Yes-A subjects, negative binomial forms were fitted well to the data. The Poisson and positive binomial forms also fitted well in most aortas. In some aortas, departures from the negative binomial, positive binomial, or Poisson forms could be attributed to the presence (among a total of 40 points) of a set of one to five points having accelerated fibroplasia. Atheronecrosis and accelerated fibroplasia tended to coexist in the same subjects and also to be found together in the same loci within aortas. Both features of advanced plaques were characteristic of older subjects. These results taken together affirm that several decades of progression of FIT precede an abrupt emergence of the two features of late phase atherogenesis. The findings suggest that atherosclerosis progresses by a two-phase stochastic process. In phase one, FIT evolves such that a form resembling the negative binomial is generated with approximations of the mean as a linear function of time and the standard deviation as a quadratic function of the mean. In phase two the set of points with greatest FIT acquires either atheronecrosis, or accelerated fibroplasia, or both.

Adult↗