Size and Power of Test Statistics for Gene Correlation in 2 × 2 Contingency Tables

Monte Carlo simulation of size and power of two proposed tests for linkage disequilibrium between two genes each with two alleles were investigated. Results were compared with two commonly used statistics, the correlation coefficient r and the log-odds ratio tests. Depending on the sign of the linkage disequilibrium, the new tests were found to be more powerful than either of the correlation or log-odds ratio tests. However, on average (positive and negative linkage disequilibrium) the Chi-square test using the correlation coefficient was to a small extent more powerful than the other tests.     

Individual personality and the spatial distribution of groups of grazing animals: An example with sheep

Impacts of individual personality on group distribution were investigated using sheep (Ovis aries) as a model. In an indoor exploration test, individuals who visited <4 (out of 6) objects in a novel environment were classified as ‘shy’ (n = 10), and those who visited 5 or 6 objects were classified as ‘bold’ (n = 10). Nine weeks later, using a series of groups (n = 40) of either 5 shy or 5 bold sheep, we measured distribution at pasture and responses to disturbance and the approach of a human handler. When grazing undisturbed, the mean nearest neighbour distance and spread (minimum convex hull area) of shy groups were less than those of bold groups, with shy individuals moving towards one another more often. Shy groups explored a smaller area than bold groups. When disturbed, shy sheep were more likely to stop grazing and move closer together. Shy sheep kept further away from the handler and moved faster when driven. The results demonstrate a link between personality and group distribution, suggesting that our ‘shy’ and ‘bold’ individuals may occupy different positions on the shy-bold continuum documented for other species. We discuss implications for diet composition and impacts on vegetation grazed by animals with different personalities.     

Test Statistics for Three-Factor Interaction in 2 × 2 × 2 Contingency Tables

A Monte Carlo simulation was conducted in order to determine the size and power of two proposed tests (the covariance and correlation tests) for three-factor interaction in 2 × 2 × 2 contingency tables. Results were compared to the log-odds ratio test statistic. Simulation showed the correlation test to be more conservative than the covariance test, but less so than the log-odds ratio test. However, the correlation test was the most powerful among the three tests.     

Reverse Monte Carlo Simulation: A New Technique for the Determination of Disordered Structures

Abstract

We have developed a new technique, based on the standard Monte Carlo simulation method with Markov chain sampling, in which a set of three dimensional particle configurations are generated that are consistent with the experimentally measured structure factor. A(Q), and radial distribution function, g(r), of a liquid or other disordered system. Consistency is determined by a standard χ² test using the experimental errors. No input potential is required, we present initial results for liquid argon. Since the technique can work directly from the structure factor it promises to be useful for modelling the structures of glasses or amorphous materials. It also has other advantages in multicomponent systems and as a tool for experimental data analysis.     

Some Monte Carlo Studies on the Comparison of Several Means Under Heteroscedasticity and Robustness with Respect to Departure from Normality

By using Monte Carlo studies, this paper compares the Welch test, the James test and the Brown-Forsythe test for comparing several means under heteroscedasticity. It appears that all the tests are quite robust with respect to departure from normality. The Brown-Forsythe test is at least as good as the James test and the Welch test; but the differences are so small that the choice is immaterial for practical purposes.     

The influence of parental care behaviour on localized nest spacing in smallmouth bass, Micropterus dolomieu

Synopsis I examined the consequence of territorial behaviour on localized nest spacing by male smallmouth bass, Micropterus dolomieu in Jones Bay, Lake Opeongo, Ontario. I compared observed nest spacing to that predicted from (i) territory size and shape measured using sonic tracking procedures; and (ii) 1000 simulated, randomly established nesting stocks. The observed spacing between nests (17.52 ± 1.46 m; mean ± standard error) was not different from that predicted from measurements of territory size and shape (17.60 ± 3.20 m) but was significantly greater than that predicted for randomly established nests (9.53 ± 0.06 m). Parental care-associated territorial behaviour influences the spacing between smallmouth bass nests.     

传递函数在生物组织光传输问题中的应用

本文将传递函数的概念引入生物组织光传输问题,并将传递函数理论用于面光源照射下生物组织内特定深度层面上光场强度分布的理论计算。结合Monte Carlo模拟获取脉冲相应函数,我们分析了不同面光源照射下层状组织样品透射面上的光场强度分布。理论计算结果与实验测试结果的一致性较好,这充分说明了本文建立的基于Monte Carlo模拟的传递函数方法是一种处理面光源照射下生物组织内光场空间的直接而有效的手段。     

P-values for group sequential testing

Group sequential testing procedures are widely employed in long-termclinical trials. We discuss several methods for computing theP-value following a group sequential trial based on differentoutcome-space orderings. We use a criterion defined in thispaper to compare these methods and point out interesting differences.