A Monte Carlo Study to Evaluate the Performance of Selected Tests of Homogeneity in Sparse Contingency Tables

We address the problem of tests of homogeneity in two-way contingency tables in case-control studies when the case category is subdivided into k subcategories. In this situation, we have two cells with large frequencies and 2 X k cells with frequencies that become small as k increases. We propose two ad hoc statistics in which a statistic for the sparse cells is combined with a statistic for the cells with large frequencies. We will study these tests along with the Pearson test (using a chi-square approximation) in a Monte Carlo simulation study. Two sets of null hypothesis models and two sets of alternative hypothesis models are considered. The best test for the models considered is the usual Pearson test (using an approximate chi-square distribution) although the ad hoc models are more powerful under one alternative model considered.     

On the Asymptotic Relative Efficiency of the Mantel-Haenszel Test

The Mantel-Haenszel test is optimal when the odds ratio is constant. This paper investigates the effects of departures from the assumption of a constant odds ratio on the behavior of the Mantel-Haenzel test. A simple approximation is proposed for the non-null distribution of the test statistic. Based on this approximation, the asymptotic relative efficiency of the Mantel-Haenszel test, compared to the overall χ² test for no partial association, is calculated. For the case of 2 strata, it is shown that the Mantel-Haenszel test is efficient as long as the logarithms of the odds ratios are of the same sign and their absolute values exceed 1.     

脱水速率和降温速率对葡萄柚种子超低温保存的影响

以新鲜葡萄柚(Citrus paradise)种子为材料,使用3种脱水速率处理至约20%含水量,然后用饱和盐溶液平衡至10种不同的含水量,再进行简化的二步法超低温保存;同时,以经过15 ℃、50%相对湿度(RH)条件脱水至含水量约12%的葡萄柚种子为材料,使用程序降温仪进行5个降温速率和3个预冷温度的传统二步法超低温保存。结果表明,葡萄柚种子对脱水敏感,种子含水量越低,成苗率越低。而且,脱水速率越快,对种子的损伤越大,成苗率呈现75% RH>50% RH>15% RH;冷冻处理对种子有进一步的伤害,含水量6%～8%的种子超低温保存效果最佳,但脱水速率对超低温保存的种子成苗率的影响不明显。用传统二步法超低温保存葡萄柚种子,与预冷对照相比,经液氮冷冻的种子成苗率都有明显下降。在预冷对照组中,-2.5 ℃·min^-1降温速率的种子成苗率最高,在冷冻保存中-0.5 ℃·min^-1和-0.25 ℃·min^-1的降温速率最有利于超低温保存。预冷温度从-40 ℃降至-60 ℃,未超低温处理种子的发芽率降低,但超低温处理种子的发芽率提高。     

Estimation of Error Rates by Means of Simulated Bootstrap Distributions

The bootstrap error estimation method is investigated in comparison with the known π-method and with a combined error estimation suggested by us using simulated and normally distributed “populations” in 15 and 30 characters, respectively. For small sample sizes (below the double to threefold number of characters per class) the estimates resulting from the bootstrap method are on the average too small and can no longer be accepted. Significantly better results (with an essentially lower calculation expenditure) are obtained for the π-method and the combined estimation. The variability is essentially the same for all the three methods. This applies both in the case of rather badly separated and in the case of very well separated populations. A bootstrap estimation modified by us also gives unsatisfactory results.     

Body size and food web structure: testing the equiprobability assumption of the cascade model

The cascade model successfuly predicts many patterns in reported food webs. A key assumption of this model is the existence of a predetermined trophic hierarchy; prey are always lower in the hierarchy than their predators. At least three studies have suggested that, in animal food webs, this hierarchy can be explained to a large extent by body size relationships. A second assumption of the standard cascade model is that trophic links not prohibited by the hierarchy occur with equal probability. Using nonparametric contingency table analyses, we tested this ”equiprobability hypothesis” in 16 published animal food webs for which the adult body masses of the species had been estimated. We found that when the hierarchy was based on body size, the equiprobability hypothesis was rejected in favor of an alternative, ”predator-dominance” hypothesis wherein the probability of a trophic link varies with the identity of the predator. Another alternative to equiprobabilty is that the probability of a trophic link depends upon the ratio of the body sizes of the two species. Using nonparametric regression and liklihood ratio tests, we show that a size-ratio based model represents a significant improvement over the cascade model. These results suggest that models with heterogeneous predation probabilities will fit food web data better than the homogeneous cascade model. They also suggest a new way to bridge the gap between static and dynamic food web models. Received: 3 February 1999 / Accepted: 26 October 1999     

住院医师规范化培训管理现状调查与分析

目的 调查分析医院开展住院医师规范化培训现状。方法 选取2011—2013年进入医院住院医师规范化培训基地的住院医师,采用现场发放调查问卷方法进行无记名调查分析。将调查内容分为报名招录、轮转培训、各类考核、组织管理和其他板块。结果 96.7%认为医院招录过程合理或基本合理,92.6%认为培训计划制定具有一定的合理性,90.1%住院医师能够按照规定完成培训内容,各类考核内容基本能够反映住院医师的培训水平。在众多培训期间存在困难中,依次为收入偏低、个人婚恋生育计划难以实施以及工作和学习压力过大。结论 住院医师基本认同目前医院的培训管理制度和方法,逐步提高住院医师薪酬待遇,有效疏导培训压力和加强师资队伍建设是提高住院医师培训积极性和培训质量的保证。     

综合医院住院医师规范化培训管理实践与探索

国家对住院医师规范化培训项目越来越重视,芜湖市第二人民医院紧随政策导向,贯彻实施住院医师规范化培训。通过以芜湖市第二人民医院住院医师规范化培训管理实践为例,介绍住院医师规范化培训背景、现状及管理实践,为持续改进培训管理工作提供参考。     

住院医师规范化培训中的问题及国际经验启示

目的 梳理我国住院医师规范化培训存在的问题,借鉴国际经验,提出相关政策建议。方法 对现阶段我国住院医师规范化培训存在问题和典型国家住院医师培训开展文献调研和专家咨询。结果 我国 住院医师规范化培训存在管理制度不完善,培训过程和内容不合理,考核制度不健全,动员机制不顺畅等问题。结论 根据 国际经验,提出厘清各部门分工,充分发挥行业组织的桥梁和纽带作用;加强顶层设计和政策配套,保障培训制度的落实;拓宽培养内容,加强学员考核,提高培养质量等政策建议。     

口腔颌面外科住院医师规范化培训中临床能力培养初探

住院医师规范化培训是培养具有独立执业能力和高超临床技能的专业医学人才的重要环节。通过对3年来口腔颌面外科住院医师规范化培训教学工作经验的总结,根据现代医学素质教育理念,结合口腔颌面外科的学科特点,探讨更加适合口腔住院医师规范化受训人员的教学方法,以促进受训住院医师临床实践综合能力的提高。我们在规范化培训中按纲施训,从转变临床思维模式、强调学习自主性、加强临床基本技能训练、注重人文思想的渗透等多方面入手,针对临床实践中的薄弱环节进行培训,为培养高素质医学人才奠定了基础,取得了教与培的满意效果。     

Phenology,population ecology,and rarity of the New Zealand ribbonwood aphid,Paradoxaphis plagianthi

Abstract

We measured some aspects of the population ecology of an arboreal aphid, Paradoxaphis plagianthi, that might contribute to its rarity. Models were fitted to data on the development rate and variability of solitary aphids in the laboratory, from larviposition to maturity, which were similar to those of several common European tree‐dwelling aphids. Life tables suggested that the intrinsic rate of population increase increases linearly with temperature to a maximum of 0.123/day at 20°C. Aphid colonies raised in controlled environments showed a lower rate of increase, presumably due to crowding effects. The rate of increase of field colonies was further depressed, probably reflecting the action of other background mortality factors. New data for seasonal population trends in the field matched previously published results, showing an increase in spring followed by a rapid decline and low summer populations. A caging experiment failed to detect any differences in host suitability in late spring between Plagianthus regius, the main host, and Hoheria angustifolia or Parsonsia heterophylla, which may act as “spill‐over” hosts in some circumstances. While the results do not explain the rarity of P. plagianthi, they suggest new hypotheses to target future work.     

Rates and Genomic Consequences of Spontaneous Mutational Events in Drosophila melanogaster

Because spontaneous mutation is the source of all genetic diversity, measuring mutation rates can reveal how natural selection drives patterns of variation within and between species. We sequenced eight genomes produced by a mutation-accumulation experiment in Drosophila melanogaster. Our analysis reveals that point mutation and small indel rates vary significantly between the two different genetic backgrounds examined. We also find evidence that ∼2% of mutational events affect multiple closely spaced nucleotides. Unlike previous similar experiments, we were able to estimate genome-wide rates of large deletions and tandem duplications. These results suggest that, at least in inbred lines like those examined here, mutational pressures may result in net growth rather than contraction of the Drosophila genome. By comparing our mutation rate estimates to polymorphism data, we are able to estimate the fraction of new mutations that are eliminated by purifying selection. These results suggest that ∼99% of duplications and deletions are deleterious—making them 10 times more likely to be removed by selection than nonsynonymous mutations. Our results illuminate not only the rates of new small- and large-scale mutations, but also the selective forces that they encounter once they arise.     

Computer Simulation of Two-Dimensional Continuum Flows by the Direct Simulation Monte Carlo Method

Abstract

Computer simulations using particles are an attractive method to extract microscopic information of flow phenomena [1]. The molecular dynamics (MD) method, in which Newton's equations of motions are integrated, gives the temporal development of the system. In the MD simulation of fluid flows, the computational region is limited to atomistic scales [2]. On the other hand, the direct simulation Monte Carlo (DSMC) method, in which collisions of particles are made on a probabilistic basis, has a potential of treating a realistic system with a macroscopic scale length retaining the atomistic details. The DSMC method provides an efficient way to integrate the Boltzmann equation from the rarefied gas to the near-continuum region. Bird clarified the validity of the DSMC method in the near-continuum flow region [3]. However, the DSMC method has not been applied to the continuum region and compared with the continuum hydrodynamics.     

Comparative Studies on the Estimation of Genetic Variances by Several Variance Components Estimation Method

Using a quantitative genetic model, this paper compares four different methods for estimating genetic variance components. Given various genetic parameters, data were generated and estimates computed. The number of negative estimates, the sample mean, the sample variance, and the sample mean squared error were computed for each method. It is shown that, if the genetic values are not very small, the traditional MATHER -JINKS method is at least as good as any other method. The ML method might be preferable only if the genetic values are very small and the number of loci large.     

真重组率与ELOD值和检验能力的关系

本文讨论了信息配子数为50时,ELOD值与检验能力随着真重组率变化的趋势,结果表明当2个基因座之间的真重组率小于或等于0?15时,连锁分析得到的结果比较可靠。 Abstract:The change of ELOD score and power was studied under the real recombination rates.A total of 50 informative meioses were used in the study as the sample size.The results showed that the linkage analysis was more reliable if the real combination rates between two loci were equal to or smaller than 0.15.     

直接前方入路与直接外侧入路人工全髋关节置换术的临床效果比较研究

目的:探讨平卧位直接前方入路(DAA)与侧卧位直接外侧入路(DLA)对行初次全髋关节置换术(THA)患者髋关节功能、平衡功能和步态参数的影响。方法:选取2018年2月～2019年10月期间我院收治的初次THA患者97例,根据入路方式的不同随机分为A组(n=47)和B组(n=50),A组行侧卧位DLA,B组行平卧位DAA,比较两组髋关节功能、影像学参数、平衡功能和步态参数,记录两组术后并发症发生率。结果:术后1周、1个月、3个月及6个月两组髋关节Harris评分(HHS)、Berg平衡量表评分(BBS)依次升高,且B组高于A组(P0.05)。B组手术时间长于A组,术中出血量少于A组,切口长度、初次下床行走时间短于A组(P0.05)。术后3个月、6个月两组步频、步速、步长依次升高,且B组高于A组(P0.05)。两组并发症发生率对比,组间比较未见统计学差异(P0.05)。两组术后6个月髋臼假体外展角、前倾角对比,组间比较无显著差异(P0.05)。结论:与侧卧位DLA相比,初次THA患者行平卧位DAA可获得与其相当的手术效果,同时能更好地改善患者髋关节功能、平衡功能和步态,且安全性有保障。     

Some Asymptotic Tests for the Equality of the Covariance Matrices of Two Dependent Bivariate Normals

For the problem of testing the equality of the covariance matrices of two dependent bivariate normals, five asymptotic tests are explicitly derived in this paper. Small sample performances of these tests are compared by simulating levels of significance and powers, and recommendation is made of the ones that have good performance. The recommended tests are then applied to real data from a crossover bioequivalence trial. Asymptotically distribution-free versions of the tests derived here are also presented.     

The Reaction Rates of NO with Horseradish Peroxidase Compounds I and II

In this study the reactions between nitric oxide (NO) and horseradish peroxidase (HRP) compounds I and II were investigated. The reaction between compound I and NO has biphasic kinetics with a clearly dominant initial fast phase and an apparent second-order rate constant of (7.0 +/- 0.3) x 10(5) M(-1) s(-1) for the fast phase. The reaction of compound II and NO was found to have an apparent second-order rate constant of k(app) = (1.3 +/- 0.1) x 10(6) M(-1) s(-1) or (7.4 +/- 0.7) x 10(5) M(-1) s(-1) when measured at 409 nm (the isosbestic point between HRP and HRP-NO) and 419 nm (lambda(max) of compound II and HRP-NO), respectively. Interestingly, the reaction of compound II with NO is unusually high relative to that of compound I, which is usually the much faster reaction. Since horseradish peroxidase is prototypical of mammalian peroxidases with respect to the oxidation of small substrates, these results may have important implications regarding the lifetime and biochemistry of NO in vivo after inflammation where both NO and H(2)O(2) generation are increased several fold.