The micronucleus test: statistical design and analysis.

Alternative statistical procedures are discussed which may be employed to compare the incidences among treatment groups of micronucleated polychromatic and normochromatic erythrocytes and their ratios. Comparison of incidences of micronucleated polychromatic erythrocytes using a sequential sampling strategy based on the negative binomial distribution is shown to require fewer animals for the same sensitivity of test than a similar procedure based on the binomial distribution. The sequential test is superior, both in power and number of animals required, to an alternative 1-stage test based on the same distribution. The procedure described permits the investigator to optimize the number of animals in each test group and the number of cells counted per animal to detect a predetermined increase in the incidence of micronucleated cells over that observed in the control population within chosen limits of type I and type II error. An alternative sequential approach based on the binomial distribution is presented, which is applicable when the number of cells analyzed per animal is variable.     

Note on a problem in probit analysis

The statistical treatment of dosage-mortality data when the number of survivors is counted but not the total number of organisms in each sample, the latter being estimated from an untreated sample, has been discussed by Wadley (1949), on the assumption of Poisson variation in the number of organisms per sample. The procedure to be followed when a wider hypothesis is made that the number of organisms has a negative binomial distribution is described here; both the arithmetical analysis of the results and the optimum arrangement of the samples are considered.     

Dose-response and thresholds in mutagenicity studies: a statistical testing approach

The analysis of dose-response relationships is an important objective in toxicology, and one in which both modelling and testing approaches are used. One particular question is whether a threshold exists at low doses. The concept of a pragmatic threshold is used, i.e. low doses with biologically unimportant effects are assumed to be threshold doses. "Biologically unimportant" means, in statistical terms, a lower effect than the effect of the negative control, or at least a just-tolerable margin delta higher than the effect of the negative control. Therefore, threshold doses can be tested in terms of a one-sided hypothesis of equivalence. A new approach is proposed, assuming, at the least, that the low dose is a threshold dose, and the highest dose is superior to the negative control. By analogy to the k-fold rule commonly used in mutagenicity studies, tests on ratio-to-control are used. The a priori definition of the threshold margin is inherently needed. A further approach proposes the analysis of dose-response relationships by means of order-restricted inference (the so-called trend test). A modification of a multiple-contrast test is used, in which only those contrasts are included that are sensitive for no effects at low doses. A further modification treats the complicated, but real, problem of simultaneous existence of a threshold, a monotonic increase, and a downturn effect at high dose(s). A parametric procedure is considered, together with an extension for proportions. The important problem of a priori sample size definition is discussed. The approaches are demonstrated by means of examples based on real data.     

On the use of the Kolmogorov-Smirnov statistical test for immunofluorescence histogram comparison

BACKGROUND: The problem considered is the quantitative comparison of immunofluorescence frequency distributions in order to detect their differences of biological significance, i.e., to evaluate the potential positivity of a cell sample with respect to negative control cells. The Kolmogorov-Smirnov (KS) statistical test, proposed in the literature for this purpose, is examined and discussed through its application to a set of experimental measurements. It is shown that even differences due to the stain procedure or to instrumental biases may be considered significant by the test implemented in the standard form. METHODS: In order to ensure valid results, it is necessary to take into account the various sources of variation in the specific experimental context. A procedure is proposed that uses the KS statistics as a reference for determining an appropriate estimate of the overall variability in the control data. This estimate is derived from the comparisons of the cumulative distributions associated with repeated measurements of the negative cell sample. RESULTS AND CONCLUSIONS: The KS-related index thus defined provides a tool for assessing the potential positivity of a cell sample, since it allows to distinguish between statistical and biological significance of the difference between the histogram to be tested and the set of control data. In particular, if a cell sample is not included in the control variability, either a positive cell subpopulation is present, or all cells are positive. Instead, for a sample included in the control variability, the difference will be not biologically meaningful, even if statistically significant. Moreover, when a purely positive control sample is also available, it is possible to derive a measure of the precision at which a true biological positivity can be detected. Finally, since the index is not absolute, but relative to the features of the instrumentation, of the antibodies and of the fluorochromes used, it represents a quantitative measure of the stability and reproducibility of the measurement process and could be used for quality control of flow cytometric experiments in immunofluorescence.     

Statistical criteria for evaluating chemicals as positive or negative in the hepatocyte/DNA repair assay

The usefulness of the hepatocyte/DNA repair assay was enhanced when statistical techniques were applied to the evaluation of a chemical as positive or negative. Using our test procedure, we are 95% confident that the false positive rate is less than 1% if the net nuclear grain count for the test chemical is 3 counts higher than the solvent control for the same animal. Additionally, quantitation of the proportion of cells in repair should be used to corroborate the results of the net nuclear grain count and is recommended for inclusion in the criteria for evaluating a chemical.     

Statistical analysis of in vivo rodent micronucleus assay

The in vivo rodent micronucleus assay (MNC) is widely used as a cytogenetic assay to detect the clastogenic activity of a chemical in vivo. MNC is one of three tests in a battery recommended by the fourth International Conference on Harmonization (ICH4) of Genotoxicity Guidelines. As such it has been accepted by many regulatory authorities. However, the determination of a positive result in a genotoxicity test, including MNC, has been an issue of debate among toxicologists and biometricians. In this presentation we compare several statistical procedures that have been suggested for the analysis of MNC data and indicate which one is the most powerful. The standard protocol of MNC has at least three dose levels plus the control dose and uses at least four animals per group. For each animal, 2000 polychromatic erythrocytes (PCE) are counted. Two statistical procedures can be employed, either alone or jointly, for the analysis of the MNC dose-response curve. These are the Cochran-Armitage (C-A) trend test and the Dunnett type test. For performing Dunnett type tests, toxicologists often use negative historical control rate for the estimate of the concurrent negative control rate. Some toxicologists emphasize the reproducibility of assay results instead of the dose-response relationship for the important criterion [J. Ashby, H. Tinwell, Mutat. Res. 327 (1995) 49-55; for the rebuttal see M. Hayashi, T. Sofuni, Mutat. Res. 331 (1995) 173-174]. The following three procedures are currently employed in toxicology labs for the evaluation of MNC result. The assay response is deemed positive if it is detected by (i) the C-A trend test alone, (ii) both the C-A trend test and the Dunnett type test and (iii) either the C-A trend test or the Dunnett type test. Using Monte Carlo simulation, we first find for each procedure, sizes of tests which yield the experiment-wise type I error rate of 0.05 and show that the procedure (ii) is the most powerful against the alternatives of monotone increase. The procedure (ii) which originated from Hayashi's three-step procedure was coded in C and termed 'MNC'. The MNC software program is available in the public domain through the ftp.     

A SIMPLE ALTERNATIVE TO GENERALIZED PROCRUSTES ANALYSIS: APPLICATION TO SENSORY PROFILING DATA

A statistical method for analyzing sensory profiling data obtained by means of fixed vocabulary or free choice profiling is discussed. The most interesting feature of this method is that it involves only simple statistical treatment and can therefore be performed using standard software packages. The outcomes of this method are compared to those of Generalized Procrustes Analysis on the basis of two data sets obtained, respectively, by means of fixed vocabulary and free choice profiling. A significance test is also discussed in order to assess whether the overall configuration of the products is meaningful. This significance test is based upon a simulation study involving the permutation procedure.     

The theory and practice of constructing calibration curves in biodozimetry

The methodical peculiarities of experimental construction of regression "dose-effect" relationships used for the dose reconstruction are discussed. The method of computer simulations is applied to study the efficiency of different statistical procedures for plotting regression curves as well as the dependence of errors in dose prediction on the volume of examined material and on the choice of doses for a calibration curve. The causes of essential variability of calibrations obtained by different teams of researchers are discussed. A number of methodical recommendations is given for statistical processing of cytogenetic data. The procedure of constructing calibration dose dependence of the frequency of dicentrics on the basis experiments with in vitro gamma-irradiation of lymphocytes from blood samples of 5 donors is considered in detail. The expressions for statistical errors occurring in the dose reconstruction made on the base of the frequency of aberrations were derived and checked by the computer experiment.     

Feature detection with controlled error rates in LC/MS images

The Median M-N rule is a feature detection algorithm to detect peptide signals in Liquid Chromatography/Mass Spectrometry (LC/MS) images. As the procedure does not adequately control the statistical errors, we investigate an extension of the Median M-N rule to compute a statistical bound on the false-positive rate. We then study the false-negative rate and provide insights on the types of signal that can be detected by the M-N rule and the limit of detection. The resulting feature detection algorithm, which we term Quantile M-N rule, can be used in most feature detection algorithms to provide statistical control of the false-positive and false-negative rate.     

Implicit testing of odor memory: instances of positive and negative repetition priming.

The study provides a test and evaluation of a new repetition priming procedure designed to solve problems in investigating olfactory-specific priming. Although the results did not reveal any overall priming effect, a post-hoc analysis showed that incorrectly identified odors were more quickly processed than control odors, whereas correctly identified odors were processed more slowly These results are discussed and interpreted as instances of positive and negative repetition priming respectively.     

Analysis of Dichotomized Factorial Data Using Cox's Proportional Hazards Model and Related Tests

This paper describes how Cox's Proportional Hazards model may be used to analyze dichotomized factorial data obtained from a right-censored epidemiological study where time to response is of interest. Exact maximum likelihood estimates of the relative mortality rates are derived for any number of prognostic factors, but for the sake of simplicity, the mathematical details are presented for the case of two factors. This method is not based on the life table procedure. Kaplan-Meier estimates are obtained for the survival function of the internal control population, Which are in turn used to determine the expected number of deaths in the study population. The asymptotic (large sample) joint sampling distribution of the relative mortality rates is derived and some relevant simultaneous and conditional statistical tests are discussed. The relative mortality rates of several prognostic factors may be jointly considered as the multivariate extension of the familiar standard mortality ratio (SMR) of epidemiological studies. A numerical example is discussed to illustrate the method.     

心理干预对高血压合并脑梗塞患者负性情绪及生活质量的影响

目的:探讨心理干预措施对高血压合并脑梗塞患者负性情绪及生活质量的影响。方法:本次选择的研究对象共92例,均为住院的高血压合并脑梗塞患者,采用简单随机分组方法,分为干预组和对照组,每组46例。对照组给予常规治疗及护理,干预组在对照组的基础上给予心理干预。在入组时、入组后1个月采用抑郁自评量表(SDS)、焦虑自评量表(SAS)、症状自评量表(SCL一90)作为测评工具,测评两组患者干预前后负性情绪和生活质量情况。结果:入组时两组患者的SDS评分、SAS评分及SCL-90各项分值比较差异无统计学意义(P0.05);干预治疗1个月后干预组较对照组患者的SDS评分、SAS评分及SCL-90各项分值均降低,差异有统计学意义(P0.05)。结论:心理干预不仅能缓解患者抑郁焦虑等负性情绪,而且有利于患者生活质量的提高。     

Computer assisted simulations and molecular graphics methods in molecular design

A survey is presented of computer-assisted statistical mechanical methods. The general theoretical background is described and special methods are discussed in detail. Practical procedures allowing for the calculation of binding energies are examined. A recent perturbation-relaxation procedure is summarized.     

Statistical Analysis of Chromatid Interference

The nonrandom occurrence of crossovers along a single strand during meiosis can be caused by either chromatid interference, crossover interference or both. Although crossover interference has been consistently observed in almost all organisms since the time of the first linkage studies, chromatid interference has not been as thoroughly discussed in the literature, and the evidence provided for it is inconsistent. In this paper with virtually no restrictions on the nature of crossover interference, we describe the constraints that follow from the assumption of no chromatid interference for single spore data. These constraints are necessary consequences of the assumption of no chromatid interference, but their satisfaction is not sufficient to guarantee no chromatid interference. Models can be constructed in which chromatid interference clearly exists but is not detectable with single spore data. We then extend our analysis to cover tetrad data, which permits more powerful tests of no chromatid interference. We note that the traditional test of no chromatid interference based on tetrad data does not make full use of the information provided by the data, and we offer a statistical procedure for testing the no chromatid interference constraints that does make full use of the data. The procedure is then applied to data from several organisms. Although no strong evidence of chromatid interference is found, we do observe an excess of two-strand double recombinations, i.e., negative chromatid interference.     

The mouse bioassay for the detection of estrogenic activity in rodent diets: I. A standardized method for conducting the mouse bioassay

A standardized procedure was developed for conducting the mouse bioassay for detecting estrogenic activity in rodent diets. Studies were conducted with CD-1 mice to determine the appropriate weaning age and length of bioassay period. Uterine growth curves were generated from mice weaned at 15 days of age and fed a negative control diet until 28 days of age. These mice showed slow regular increases in uterine weights from 15 22 days of age followed by rapid uterine growth in some mice from 24 to 28 days of age. Estrogenic bioassays using female mice weaned at 15 days of age and fed the positive control diets containing 4 or 6 ppb diethylstilbestrol (DES) demonstrated significant (P less than 0.05) increases in uterine weight and in uterus to body weight (U:BW) ratios over those of mice fed the negative control diet without DES for 5, 7 or 9 days after weaning. In contrast, mice weaned at 17 days of age showed significant (P less than 0.05) increases in uterine weight and in U:BW ratios only at 5 days after weaning. Six ppb DES was required in the positive control diet to produce a 1.5 fold increase in the U:BW ratio over those of mice fed the negative control diet. It was concluded that mice should be weaned at 15 days of age and that the bioassay period should be terminated at 7 days, when the mice are 22 days old, for best reproducible results. The criteria for a valid bioassay should include the demonstration of a significant statistical increase in the U:BW ratios of mice fed the DES positive diet over those of mice fed the negative control diet.     

EXCEL在农药田间药效试验统计分析中的应用

根据方差分析原理,利用EXCEL编制了农药田间药效试验统计分析程序。用户只需输入试验的原始数据,即可快速、准确地计算出药剂的防治效果,方差分析结果及药剂间的多重比较。     

Insecticidal phytotoxicity and cereal grain yield

A simple statistical procedure has been derived from field experimental data on insecticidal seed coatings for control of wheat bulb fly larvae to measure the direct effect of the insecticides on the yield of wheat.     

Prediction of electromagnetic field distributions inside biological bodies by using an inverse scattering procedure based on a statistical cooling algorithm

This paper presents an inverse scattering procedure based on a statistical cooling algorithm to predict the electromagnetic field inside a biological body. By knowing only the scattered electric field distribution in a set of observation points external to the biological model, this method seems to be able to predict the electromagnetic field distributions in the investigation domain, minimizing a suitable cost function. To this end, a numerical statistical procedure is used, which allows to treat functions with a large number of unknowns in an efficient manner and to exploit the so called a priori knowledge in the reconstruction process. Some preliminary results are reported, concerning simplified biological geometries, which clearly show the capabilities and effectiveness, and also the current limitations of the proposed approach. Finally, further advances for the proposed imaging technique are indicated and discussed.     

玉米赤霉烯酮在小鼠体内的致突变性研究*

用小鼠骨髓细胞微核试验和染色体畸变试验评价了赤霉病麦毒素之一玉米赤霉烯酮的体内致突变效应。玉米赤霉烯酮的试验剂量为0,0.1,1.0,10.0,100.0mg/kg体重,以环磷酰胺为阳性对照。实验结果表明,玉米赤霉烯酮各试验剂量组的微核发生率和染色体畸变率与阴性对照组相比均无显著性统计学差异,亦未发现有明显的性别差异。     

玉米赤霉烯酮在小鼠体内的致突变性研究

用小鼠骨髓细胞微核试验和染色体畸变试验评价了赤霉病麦毒素之一玉米赤霉烯酮的体内致突变效应。玉米赤霉烯酮的试验剂量为0,0.1,1.0,10.0,100.0mg/kg体重,以环磷酰胺为阳性对照。实验结果表明,玉米赤霉烯酮各试验剂量组的微核发生率和染色体畸变率与阴性对照组相比均无显著性统计学差异,亦未发现有明显的性别差异。