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PubMed1988

Interaction of temperature and other environmental variables influencing plant distribution.

Statistical analyses of the relationships between the patterns of distribution of plants with C4 photosynthesis and Crassulacean acid metabolism (CAM) have revealed a variety of correlations with environmental variables. The worldwide abundance of C4 grasses, relative to C3 grasses, is highly positively correlated with growing season temperature. However, microscale analyses have revealed that C4 grasses are more abundant than C3 grasses in habitats with high levels of solar irradiance and low moisture availability. There are numerous exceptions to these generalizations. C4 dicots generally are more abundant in habitats characterized by high rates of evaporation. Species possessing CAM occur in habitats having low levels of soil moisture store. In the Cactaceae such habitats also have very high potential rates of evaporation and the CAM pathway is the primary mechanism of the uptake of atmospheric CO2. In contrast many species of the Crassulaceae grow in habitats with lower potential rates of evaporation and the CAM pathway is less important or not used at all in the uptake of atmospheric CO2.

Environment↗
PubMed1990

Computerized ultrasound B-scan texture analysis of experimental fatty liver disease: influence of total lipid content and fat deposit distribution.

Statistical pattern recognition procedures allow a quantitative description of ultrasound-B-scan image texture. According to well-established animal models, different types of fatty liver disease were induced in female Wistar rats. For the correlation of the computerized ultrasound image with its underlying histology a variable tissue model based on histomorphological data, texture analysis of the histological image and biochemical measurements of total lipid, water and hydroxyproline content was created. Whereas a regional arrangement of large fat deposits leads to a significant increase in the "mean grey level" (measure of image brightness) of the ultrasound-B-scan image, there is no difference in image brightness between normal liver tissue and liver steatosis for the tissue model with diffuse homogeneous fatty infiltration. It is demonstrated by multiple linear regression analysis that the "mean grey level" of the ultrasound-B-scan image depends not only on total lipid content but even more on the histomorphological fat deposit distribution.

Animals↗
PubMed1992

Gamma distribution and house 222Rn measurements.

The statistical distribution of 222Rn measurements from basements and first floors of homes in northeastern Pennsylvania was investigated. The gamma distribution was statistically significantly superior to the normal distribution (p less than 0.005) in describing the frequency distribution of the logarithm of observed 222Rn levels. The fit to the data was closer both in the central portion and in the upper tail. The gamma distribution has certain characteristics that make it generally useful in the study of environmental toxic agents where several different exposures over a lifetime occur and must be combined, as for risk assessment or for statistical power calculations for epidemiologic studies.

Air Pollution, Indoor↗
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↗
PubMedDate not supplied

Dimensions of homo- and heteropolymeric sections of DNA synthesized by reverse transcription from globin mRNA matrices.

The lengths of globin messenger RNAs, isolated from rabbit and pigeon reticulocytes, and single-stranded complementary DNAs, synthesized from mRNA in presence of RNA-directed DNA-polymerase and oligo(dt) have been investigated by polyacrylamide gel electrophoresis under denaturing conditions. The cDNA preparations contained a fraction which corresponded in length to the alpha and beta chains of the mRNA used as a matrix. The lengthwise distribution of poly(A) sequences, isolated from globin mRNAs, corresponded to a statistical distribution, with a maximum at 75-80 nucleotides and with a maximum length of approximately 150 nucleotides. The lengthwise distribution of poly(dt) sequences, isolated from cDNA, corresponded to the poly(A) sequence distribution. It was concluded that: 1) cDNA is heterogeneous with respect to the length of poly(dt) sequences located at the 5' end of the molecule; 2) there was no selective use as primer of only that oligo(dt) which was located within the complex formed with the 5' end of the mRNA poly(A) sequence; 3) the heterogeneity of poly(DT) corresponded qualitatively to two models of template-primer interaction: selective use as a true primer of the oligonucleotide located in the complex formed with the 3' end of mRNA, and a statistical distribution of primer along the poly(A) sequence; and 4) the heterogeneity of the homopolymeric section of the cDNA may affect the kinetics of hybridization with mRNA, which possibly explains the previously observed [1] anomalous dependence of the hybridization rate on time.

Animals↗
PubMed1977

Statistical comparison of power spectra: a computer program.

A general computer program, of interest to neurobiologists, for comparison of uncorrelated power spectra is presented. The program, ALPHAF, is written in Fortran V language and is easily compiled and executed in any computer with a Fortran software package. The purpose of the program is to read power spectral density (PSD) values into a computer from digital tape and then perform the following functions: (1) compute and report power; (2) compute and report averages of the computed power values over selected frequency bands and (3) compute and report statistical standardised normal distributions for a frequency spectrum of interest. The standardised normal distribution statistic is derived by using equation 7.20, page 250 of Random data: Analysis and measurement procedures (Bendat and Piersol, 1971).

Computers↗
PubMed1988

Postnatal development of the mouse temporal muscle and effects of a fine-grained diet on the muscle spindle.

The postnatal development of the mouse temporal muscle and effects of a fine-grained diet on muscle spindles were investigated. On d 25 after birth, 3 types of extrafusal muscle fibers could be distinguished on the basis of SDH activity, but not on the basis of their diameters. And in 50-d-old mice, 3 types of the muscle fibers had different diameters each other. In intrafusal muscle fibers, the postnatal changes of the SDH activity were similar to those of extrafusal muscle fibers, but the diameter distribution showed unimodal statistical distribution from 10th to 50th postnatal day. On the other hand, in control 180-d-old mice, 80 percent of muscle spindles in the temporal muscle had complete annulospiral endings, but the ratio of muscle spindles with complete annulospiral endings was decreased significantly in mice fed a fine-grained diet. The diet also decreased the diameter of the endings significantly. These results suggest that the main changes in the morphological and functional properties of the mouse temporal muscle occur in during and early after weaning period, and that normal mastication is needed to maintain the homeostatic condition of the mouse temporal muscle.

Animals↗
PubMed1986

How should we estimate confidence intervals for a ratio, for example, between counts of colony-forming cells?

When calculating a ratio, of colony counts, for example, experimental hematologists often provide no indication of the uncertainty of the estimates, or the uncertainty is computed using a method with partially unknown properties. We have used empirical data on survival of colony-forming cells after exposure to hydroxyurea to select assumptions regarding the statistical properties of the survival ratios. Then, we have evaluated four alternative methods for constructing confidence intervals for such ratios. With simulations, the adequacy of the methods is shown to depend on the assumed statistical distributions of the data and on the number of observations in the numerator and denominator. Especially with few observations, some methods may produce misleading results. An easily calculable confidence interval, formally based on lognormal distributions, seems to be applicable to a fairly wide range of other plausible statistical distributions as well; it may be a reasonable choice in many situations. Whatever method is chosen, the confidence intervals for ratios are wide, and more data than is generally appreciated are needed for a precise determination of a ratio.

Animals↗
PubMed1988

Exposure to agricultural treatment residues: some simple statistical considerations based on monitoring data for ethoxyquin on apples.

The data examined here concern ethoxyquin levels, mainly measured in apple samples from the retail market. In this study about three hundred measurements, carried out on apples in Northern-Central Italy and recently published, are examined, with the purpose of defining the main characteristics of value statistical distribution and variability and to optimize sampling criteria. The analysis did not indicate the presence of significantly high levels or consequently significantly high risks; nevertheless, it pointed out some important aspects in data collection and evaluation. First, it appeared that the statistical distribution of data is typically nonsymmetrical, non-Gaussian, and characterized by a tail extending toward the high values. The logarithmic transformation of data appeared useful in order to obtain a Gaussian distribution. As a rule, the data variability appeared to be high. The frequency and distribution of values above the analytical threshold resulted in significant change, both in time and in space. The percentage of positive values (above the analytical threshold) appeared to vary up to a factor of 2-3, as analogously did their geometric mean.(ABSTRACT TRUNCATED AT 250 WORDS)

Environmental Monitoring↗
PubMed1992

Quantification of biological variability.

Pharmacokinetic models are usually developed to describe the kinetic behaviour of the chemical compounds in an average human body. There are however many situations were the effects of variations in a given pharmacokinetic parameter would be of interest. For example, in biological monitoring, the variability of biological data is a critical parameter when relating air and biological measures of an individual exposure. This paper reviews two possible approaches for the simulation of such variability in occupational pharmacokinetics. In the first, a simple one-compartment model is used together with statistical distributions for the intake and elimination of the compounds involved. Based on realistic distributions, this simple model is applied to the comparison of biological and air monitoring to estimate workers' exposure. The second involves a seven-compartment physiologically based pharmacokinetic model, which includes provision of the means to input satistical distributions for some of the parameters: exposures, physical workload, body height, body weight, liver function and renal function. It makes it possible to predict the pharmacokinetic response of groups of workers, who differ in their exposures and in their physiological parameters. Realistic statistical distributions are then used to describe biological monitoring variability. The advantages and disadvantages of both the simple pharmacokinetic model and the physiological model are discussed in the context of predicting and understanding variability in occupational situations. Other potential developments are also considered.

Environmental Monitoring↗
PubMed1990

Human choriogonadotropin (hCG): comparisons between determinations of intact hCG, free hCG beta-subunit, and "total" hCG + beta in serum during the first half of high-risk pregnancy.

We have studied the concentrations of intact human choriogonadotropin (hCG) and the free hCG beta-subunit in blood samples from singleton pregnancies at risk for habitual or threatened abortion. The samples were obtained weekly between the 6th and 12th weeks and in the 14th and 16th weeks of gestational age. The concentrations of intact hCG, of the free hCG beta-subunit, and of "total" hCG (i.e., intact hCG and the free hCG beta-subunit: hCG + beta) were measured in serum by specific immunoassays. The distributional statistics (the 5th, 50th, and 95th percentiles) of "total" hCG + beta and of intact hCG showed very similar patterns, whereas the response curves for the free hCG beta-subunit showed very much lower serum concentrations. From these data we also estimated distributional statistics of the percent molar ratios of free hCG beta-subunit to intact hCG. We conclude that (a) the relatively small proportion of free hCG beta-subunit in serum during the first half of singleton pregnancy is far too low to interfere with the applied "total" hCG assay, as compared with the serum values obtained for intact hCG, and (b) the percent molar ratios of free hCG beta-subunit to intact hCG, or to "total" hCG + beta, never exceeded 1.0% throughout the period of pregnancy studied.

Abortion, Threatened↗
PubMed1978

[Distribution pattern, statistical analysis and correlation of selenium levels in swine selenium-indicating organs].

There is a potential risk of excessive selenium levels in organs of swine, resulting in toxicity and residues in pork, or selenium deficit. Therefore, random selenium mean values in "selenium-indicating" organs of pigs selected from suspicious populations were compared with mean and limiting values (reference or normal values) recorded from animals with intact metabolism. Prerequisites required for such comparative assessment included the availability of estimated variance values and knowledge of the presence of abscence of agreement between normal distribution and empirical frequency distribution for the population concerned. Knowledge must be available also on the informative value of measured selenium data in blood plasma and their relevance to the general selenium situation in the organism and muscle at large. These were some of the problems studied by determining selenium levels in the liver, kidneys, blood plasma, and M. longissimus dorsi. Organic selenium concentrations were found to be distributed with right axis deviation but almost normal. The parameters established were typical of the majority of data known from literature. Those date, however, are quite variable, so that the need for independently prepared reference values cannot be abandoned. Correlation analysis showed reciprocal relationships between selenium levels in blooc plasma, liver, and muscles but much less correlation between these, on the one hand, and selenium in kidneys, on the other. The correlations between blood plasma and muscle selenium were close enough to take blood plasma values recorded from the living animal as reference from which to draw conclusions as to the muscular selenium state.

Animals↗
PubMed1985

Mechanisms of CML hyporesponsiveness in long-term renal allograft recipients.

Long-term, HLA disparate, renal allograft recipients were assessed by a dose-dependent CML (cell-mediated lympholysis) assay for evidence of donor-specific CML hyporesponsiveness. The frequency of cytolytic T-cell (CTL) precursors capable of responding to donor alloantigen was also examined by a limiting-dilution assay and application of Poisson distribution statistics. Four recipients were found to have depressed CML responses against donor class I HLA antigens (mean 2-5% specific lysis), whereas significant responses against third party targets were noted (15-60% specific lysis). These data are consistent with an antigen-specific defect in the recipient CTL effector mechanism. To determine whether or not this may be due to a deletion of anti-donor alloreactive cells, a sensitive limiting-dilution assay was developed in conjunction with Poisson distribution statistics to obtain the frequency of both anti-donor and anti-third party CTLp present in recipient PBLs. A simultaneous reduction in the number of alloreactive clones and the presence of an active suppressor population were defined, suggesting that several mechanisms may operate concurrently in long-term renal allograft recipients with well-functioning grafts.

Cytotoxicity, Immunologic↗