Sample size estimation for comparing rates of change in K-group repeated count outcomes

Sample size estimation for comparing the rates of change in two-arm repeated measurements has been investigated by many investigators. In contrast, the literature has paid relatively less attention to sample size estimation for studies with multi-arm repeated measurements where the design and data analysis can be more complex than two-arm trials. For continuous outcomes, Jung and Ahn (2004 Jung, S., Ahn, C. (2004). K-sample test and sample size calculation for comparing slopes in data with repeated measurements. Biometrical J. 46(5):554–564.[Crossref], [Web of Science ®] , [Google Scholar]) and Zhang and Ahn (2013 Zhang, S., Ahn, C. (2013). Sample size calculation for comparing time-averaged responses in k-group repeated measurement studies. Comput. Stat. Data Anal. 58:283–291.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) have presented sample size formulas to compare the rates of change and time-averaged responses in multi-arm trials, using the generalized estimating equation (GEE) approach. To our knowledge, there has been no corresponding development for multi-arm trials with count outcomes. We present a sample size formula for comparing the rates of change in multi-arm repeated count outcomes using the GEE approach that accommodates various correlation structures, missing data patterns, and unbalanced designs. We conduct simulation studies to assess the performance of the proposed sample size formula under a wide range of designing configurations. Simulation results suggest that empirical type I error and power are maintained close to their nominal levels. The proposed method is illustrated using an epileptic clinical trial example.     

中央环保督察、地方政府回应与环境治理取向

中央环保督察以一种“高位推动”的跨层级治理方式增强了环保执法刚性约束力，由此刺激出各级地方政府多样化的回应方式与治理取向。基于府际关系理论建构的“督察—回应”分析框架对地方政府回应中央环保督察的行动逻辑考察发现:在环保考核的压力下，地方政府采取消极的“一刀切”回应方式，虽能在短时间内缓解中央环保督察所带来的问责压力，转移“治污”主体责任，降低公众对环保约谈的关注度与社会舆论的放大程度，但由此衍生出的多重次级风险不仅会弱化地方政府公信力，也会影响地方经济发展。而作为一种积极的“切一刀”回应取向，既实现了精准治理、典型治理和分类治理的有机结合，也有助于提升地方环境政策执行绩效，实现环境“治理有效”。“一刀切”转向“切一刀”意味着基层生态环境治理能力逐渐提升，更是环境治理体系和治理能力现代化的必然要求。     

具有GARCH（1，1）-正态误差项的非对称单位根检验研究

摘　　要:理论研究表明许多经济变量呈现出非对称的门限自回归（TAR）或动态门限自回归（M-TAR）数据生成机制,因而非对称单位根检验就成为该领域的主要研究方向之一。本文对非对称单位根检验Enders-Granger方法在GARCH（1,1）-正态误差项下的检验水平与检验势作了系统的仿真研究。研究表明：GARCH（1,1）-正态误差项的TAR或M-TAR模型会对该方法的检验水平和检验势产生重要影响。     

Speciation, its ecological and biogeographical consequences

I studied the effect of treehole (microhabitat) size distribution in local habitats on geographic difference in aquatic metazoan community structure by comparing differences between two sites on Iriomote Island, and between Iriomote Island (subtropical) and Tsushima Island (temperate), in southwestern Japan. In treeholes at each local site, the amount of litter, the species richness and total biomass of metazoa were positively correlated with treehole capacity. Between the two sites on Iriomote Island (Shirahama and Komi), the amount of litter, biomass and species number per treehole was greater at Komi where the mean and variance of treehole size were greater, while the dependencies of these parameters on treehole capacity were common to both sites. Total species number was larger at Komi (2 predators and 20 saprophages) than at Shirahama (1 predator and 19 saprophages). Most of the dominant taxa colonized larger treeholes with higher probabilities, although one taxa showed the opposite trend. Treeholes on Tsushima were smaller than those on Iriomote. The metazoan fauna in treeholes consisted of 15 saprophages on Tsushima, being less richer than that on Iriomote Island which had 2 predators and 21 saprophages. However, the dependencies of litter amount and biomass on treehole capacity did not differ significantly between the islands, although treeholes on Iriomote harbored a greater number of species per treehole than those on Tsushima. This study indicated that there are general correlates between community structure within individual treeholes (infracommunity structure) and treehole capacity (microhabitat size). Therefore, microhabitat-size distribution is potentially a significant constraint of local community structure, and its variation may contribute to the variation in local and regional species richness.     

湖南省上市公司资产结构与公司绩效的相关性研究

以2003-2012 年间湖南省上市公司为样本,采用多元线性回归对其资产结构与公司绩效之间的关系进行了实证研究.结果表明,湖南省上市公司流动资产比率与公司绩效呈微弱的正相关关系,固定资产比率对公司绩效的影响不显著,总资产周转率与公司绩效呈显著正相关关系.研究还发现,公司规模与公司绩效呈显著正相关关系,资产负债率与公司绩效呈显著负相关关系.     

Considerations on jury size and composition using lower probabilities

The use of lower probabilities is considered for inferences in basic jury scenarios to study aspects of the size of juries and their composition if society consists of subpopulations. The use of lower probability seems natural in law, as it leads to robust inference in the sense of providing a defendant with the benefit of the doubt. The method presented in this paper focusses on how representative a jury is for the whole population, using a novel concept of a second ’imaginary’ jury together with exchangeability assumptions. It has the advantage that there is an explicit absence of any assumption with regard to guilt of a defendant. Although the concept of a jury in law is central in the presentation, the novel approach and the conclusions of this paper hold for representative decision making processes in many fields, and it also provides a new perspective to stratified sampling.     

Keeping Surveys Valid,Reliable, and Useful: A Tutorial

This tutorial focuses on how to produce reliable and generalizable data from random‐digit‐dialing (RDD) landline and cell phone surveys. The article notes that RDD response rates have declined and explores the impact of this pronounced decline. The tutorial addresses order, response mode, and many other biases, sample size, cooperation and response rates, weighting, and hybrid designs‐all using examples from risk analysis to illustrate the key points. The article ends with a brief review of the advantages and disadvantages of major Internet and paper surveys tools, and how these can be molded and sometimes combined in repeated, longitudinal, and other designs to answer questions about risk preferences and perceptions.     

Back to basics: explaining sample size in outcome trials,are statisticians doing a thorough job?

Time to event outcome trials in clinical research are typically large, expensive and high‐profile affairs. Such trials are commonplace in oncology and cardiovascular therapeutic areas but are also seen in other areas such as respiratory in indications like chronic obstructive pulmonary disease. Their progress is closely monitored and results are often eagerly awaited. Once available, the top line result is often big news, at least within the therapeutic area in which it was conducted, and the data are subsequently fully scrutinized in a series of high‐profile publications. In such circumstances, the statistician has a vital role to play in the design, conduct, analysis and reporting of the trial. In particular, in drug development it is incumbent on the statistician to ensure at the outset that the sizing of the trial is fully appreciated by their medical, and other non‐statistical, drug development team colleagues and that the risk of delivering a statistically significant but clinically unpersuasive result is minimized. The statistician also has a key role in advising the team when, early in the life of an outcomes trial, a lower than anticipated event rate appears to be emerging. This paper highlights some of the important features relating to outcome trial sample sizing and makes a number of simple recommendations aimed at ensuring a better, common understanding of the interplay between sample size and power and the final result required to provide a statistically positive and clinically persuasive outcome. Copyright © 2009 John Wiley & Sons, Ltd.     

A Class of Sampling Two Units with Probability Proportional to Size

A class of sampling two units without replacement with inclusion probability proportional to size is proposed in this article. Many different well known probability proportional to size sampling designs are special cases from this class. The first and second inclusion probabilities of this class satisfy important properties and provide a non-negative variance estimator of the Horvitz and Thompson estimator for the population total. Suitable choice for the first and second inclusion probabilities from this class can be used to reduce the variance estimator of the Horvitz and Thompson estimator. Comparisons between different proportional to size sampling designs through real data and artificial examples are given. Examples show that the minimum variance of the Horvitz and Thompson estimator obtained from the proposed design is not attainable for the most cases at any of the well known designs.     

On Approximability of Boolean Formula Minimization

For a Boolean function given by a Boolean formula (or a binary circuit) S we discuss the problem of building a Boolean formula (binary circuit) of minimal size, which computes the function g equivalent to , or -equivalent to , i.e., . In this paper we prove that if P NP then this problem can not be approximated with a good approximation ratio by a polynomial time algorithm.