Impact Factors and the Central Limit Theorem: Why citation averages are scale dependent     

Manolis Antonoyiannakis 《Journal of Informetrics》2018,12(4):1072-1088

Citation averages, and Impact Factors (IFs) in particular, are sensitive to sample size. Here, we apply the Central Limit Theorem to IFs to understand their scale-dependent behavior. For a journal of n randomly selected papers from a population of all papers, we expect from the Theorem that its IF fluctuates around the population average μ, and spans a range of values proportional to $\sigma /\sqrt{n}$, where σ² is the variance of the population's citation distribution. The $1/\sqrt{n}$ dependence has profound implications for IF rankings: The larger a journal, the narrower the range around μ where its IF lies. IF rankings therefore allocate an unfair advantage to smaller journals in the high IF ranks, and to larger journals in the low IF ranks. As a result, we expect a scale-dependent stratification of journals in IF rankings, whereby small journals occupy the top, middle, and bottom ranks; mid-sized journals occupy the middle ranks; and very large journals have IFs that asymptotically approach μ. We obtain qualitative and quantitative confirmation of these predictions by analyzing (i) the complete set of 166,498 IF & journal-size data pairs in the 1997–2016 Journal Citation Reports of Clarivate Analytics, (ii) the top-cited portion of 276,000 physics papers published in 2014–2015, and (iii) the citation distributions of an arbitrarily sampled list of physics journals. We conclude that the Central Limit Theorem is a good predictor of the IF range of actual journals, while sustained deviations from its predictions are a mark of true, non-random, citation impact. IF rankings are thus misleading unless one compares like-sized journals or adjusts for these effects. We propose the Φ index, a rescaled IF that accounts for size effects, and which can be readily generalized to account also for different citation practices across research fields. Our methodology applies to other citation averages that are used to compare research fields, university departments or countries in various types of rankings.  相似文献   

Confidence in prior knowledge,self-efficacy,interest and prior knowledge: Influences on conceptual change     

《Contemporary educational psychology》2014,39(2):164-174

This study explored how confidence in prior knowledge, self-efficacy, interest, and prior knowledge interact in conceptual change learning. One hundred and sixteen college students completed an assessment of confidence in prior knowledge, self-efficacy, interest, prior scientific understanding, and prior misconceptions before reading a refutation text on seasonal change. Students’ misconceptions and scientific understanding of seasonal change was then assessed before and after reading a refutation text, and again at a two week delayed posttest. Three profiles of students emerged based on their confidence in prior knowledge, self-efficacy, interest, prior scientific understanding, and prior misconceptions. The profiles included: (1) Low (low confidence, self-efficacy, interest, and prior scientific understanding and high prior misconceptions), (2) mixed (high confidence, self-efficacy, and interest, but low prior scientific understanding and high prior misconceptions), and (3) high (high confidence, self-efficacy, interest, and prior scientific understanding and low prior misconceptions). Results indicated that the mixed profile appeared to be most productive for conceptual change and that learner characteristics most productive for conceptual change learning may differ from those most productive in other learning situations.  相似文献   

一类向量值映射与其边缘映射的次微分     

黄龙光 《韩山师范学院学报》1997,18(2):38-42

本文研究拓扑线性空间上一类向量值映射与其边缘映射的次微分的关系。  相似文献   

具变系数的二阶中立型微分方程解的振动性     

王其如 《衡阳师范学院学报》1992,(6)

本文研究具有变系数的二阶非线性中立型方程和线性中立型方程建立了方程(1)和(16)的所有有界解振动的充分条件,其条件是“sharp"的,也给出了方程(1)的线性化极限振动准则。所得结果推广了文《二阶非线性中立型微分方程解的振动准则》(钱祥征等,湖南教学年刊Vol.10No.1—2,(1990),101—108)中的结论。  相似文献   

A Computer Application of Recurrence Formulae for Means and Standard Deviations     

JOHN S. CROUCHER 《Teaching Statistics》1984,6(3):81-82

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运动员竞赛焦虑状态的分析     

武炜 《襄樊学院学报》2011,32(11):57-59

以参加第六届全国农运会田径项目的150名运动员作为研究对象,采用＂运动竞赛状态焦虑量表＂（简称CSAI-2问卷）为测试工具进行调查.结果表明：（1）不同性别的运动员竞赛焦虑状态各维度上不存在显著差异,但女运动员竞赛焦虑状态各因素得分略高于男运动员;（2）不同运动年限的运动员竞赛焦虑状态各维度上存在显著差异,运动年限越长竞赛焦虑状态各因素得分越高;（3）不同专项的运动员竞赛焦虑状态各维度不存在显著差异.  相似文献   

浅议黑格尔的无限观     

彭冰冰 《桂林师范高等专科学校学报》2005,19(1):5-8

黑格尔把无限分为两种：一种叫做“真无限”；一种叫做“坏无限”。他认为传统的无限观是形而上学的“坏无限”，无限与有限是绝对对立的。而“真无限”则认为有限和无限之间没有不可超越的界限，它是无限和有限的自身发展起来的统一。黑格尔通过对无限的划分，把真无限理解为有限和无限彼此自我否定，自我扬弃后的对立统一，进而达到他所谓的“绝对精神”。  相似文献   

谈饭店经营中的人情味     

毛丽蓉 《金华职业技术学院学报》2001,1(1):92-94

人情味应该是摒弃了世俗的功利和偏见，它不是从业的手段，而应是饭店经营追求的一种境界。能够令宾客觉得温暖、亲切的人情味的饭店，是能够在顾客和员工中赢得人心的饭店。  相似文献   

一类广义Liénard型方程的极限环     

杨启贵 《蒙自师范高等专科学校学报》1995,(4)

本文讨论广义Lienard系统(E):x+(f(x)+k(x)x)+g(x)=0,获得了系统(E)的极限环存在,至多有一个或两个的充分条件.这些条件不仅简单和易于验证,而且推广了〔5,6〕的结果.  相似文献   

康托实数集合不可数证明中的四种错误探析     

欧阳耿 《喀什师范学院学报》2011,32(6):17-21

从逻辑、无穷观、极限论和证明的思路及具体的操作过程,分析了新发现的康托在实数集合不可数证明中所存在的四种错误,得到＂由于与现有经典无穷理论体系、经典极限论和经典数量体系密切相关的数学基础理论中所存在的缺陷,康托在这类证明中无法回避这四种很严重但却很隐蔽的错误＂的明确结论.特别是其中的逻辑错误使这样的证明无意中成了一种典型的数学魔术.  相似文献