Analytical approximations for iterated bootstrap confidence intervals

Standard algorithms for the construction of iterated bootstrap confidence intervals are computationally very demanding, requiring nested levels of bootstrap resampling. We propose an alternative approach to constructing double bootstrap confidence intervals that involves replacing the inner level of resampling by an analytical approximation. This approximation is based on saddlepoint methods and a tail probability approximation of DiCiccio and Martin (1991). Our technique significantly reduces the computational expense of iterated bootstrap calculations. A formal algorithm for the construction of our approximate iterated bootstrap confidence intervals is presented, and some crucial practical issues arising in its implementation are discussed. Our procedure is illustrated in the case of constructing confidence intervals for ratios of means using both real and simulated data. We repeat an experiment of Schenker (1985) involving the construction of bootstrap confidence intervals for a variance and demonstrate that our technique makes feasible the construction of accurate bootstrap confidence intervals in that context. Finally, we investigate the use of our technique in a more complex setting, that of constructing confidence intervals for a correlation coefficient.     

投资扩张的经济学分析

我国经济运行的态势良好,但存在的问题也不少。其中,投资盲目扩张的冲动较强是个主要矛盾。投资 受预期的影响,非理性预期是投资盲目扩张的一个充分必要条件。将科学发展观引入理性预期的概念之中,能够 提高投资决策和投资行为的科学性。建立健全正式的和非正式的制度安排,发展科学教育事业和提高全民的文化 素质,有利于形成信息的充分性和对称性。     

苍凉的欢愉--评赖少其80岁后的作品

中西文化的碰撞,为20世纪的中国画坛平添了诸多扑朔迷离的景象,也为俯仰于这一背景下的无数个体的艺术生命带来了重重疑惑和困扰.赖少其以其特殊的革命经历、独特的文化积累,在自然生命行将停止运行的关键时期凸显了其艺术生命中最本质、最原始、最朴素、最真挚和最纯净的精神境象,真正实现了中国画由传统向现代的转换过程,从而为20世纪的中国画坛绽放了一枝奇瑰的花朵.     

Expected sample moments of concomitants of selected order statistics

In this paper, the task of determining expected values of sample moments, where the sample members have been selected based on noisy information, is considered. This task is a recurring problem in the theory of evolution strategies. Exact expressions for expected values of sums of products of concomitants of selected order statistics are derived. Then, using Edgeworth and Cornish-Fisher approximations, explicit results that depend on coefficients that can be determined numerically are obtained. While the results are exact only for normal populations, it is shown experimentally that including skewness and kurtosis in the calculations can yield greatly improved results for other distributions.     

A Unified Approach to the Approximation of Multivariate Densities

Approximation of a density by another density is considered in the case of different dimensionalities of the distributions. The results have been derived by inverting expansions of characteristic functions with the help of matrix techniques. The approximations obtained are all functions of cumulant differences and derivatives of the approximating density. The multivariate Edgeworth expansion follows from the results as a special case. Furthermore, the density functions of the trace and eigenvalues of the sample covariance matrix are approximated by the multivariate normal density and a numerical example is given     

住房市场系统模型研究

从宏观层面建立了包含银行、地产商及消费者在内的住房市场系统模型,重点考虑了信贷对住房市场供需双方的金融支持,构建了住房市场系统的定量分析框架,该框架对于银行主导的住房市场具有一般性。通过中国住房市场的实证分析,证实了模型的有效性。     

Importance of interpolation when constructing double-bootstrap confidence intervals

We show that, in the context of double-bootstrap confidence intervals, linear interpolation at the second level of the double bootstrap can reduce the simulation error component of coverage error by an order of magnitude. Intervals that are indistinguishable in terms of coverage error with theoretical, infinite simulation, double-bootstrap confidence intervals may be obtained at substantially less computational expense than by using the standard Monte Carlo approximation method. The intervals retain the simplicity of uniform bootstrap sampling and require no special analysis or computational techniques. Interpolation at the first level of the double bootstrap is shown to have a relatively minor effect on the simulation error.     

Standard errors for EM estimation

The EM algorithm is a popular method for computing maximum likelihood estimates. One of its drawbacks is that it does not produce standard errors as a by-product. We consider obtaining standard errors by numerical differentiation. Two approaches are considered. The first differentiates the Fisher score vector to yield the Hessian of the log-likelihood. The second differentiates the EM operator and uses an identity that relates its derivative to the Hessian of the log-likelihood. The well-known SEM algorithm uses the second approach. We consider three additional algorithms: one that uses the first approach and two that use the second. We evaluate the complexity and precision of these three and the SEM in algorithm seven examples. The first is a single-parameter example used to give insight. The others are three examples in each of two areas of EM application: Poisson mixture models and the estimation of covariance from incomplete data. The examples show that there are algorithms that are much simpler and more accurate than the SEM algorithm. Hopefully their simplicity will increase the availability of standard error estimates in EM applications. It is shown that, as previously conjectured, a symmetry diagnostic can accurately estimate errors arising from numerical differentiation. Some issues related to the speed of the EM algorithm and algorithms that differentiate the EM operator are identified.     

城镇化、劳动分工与农村市场扩展

市场规模的扩展是影响经济增长的重要因素。在现代社会,从长期来看,市场的扩展取决于劳动分工的演进。如果没有分工的深化,就意味着没有创新和新的产业出现,市场的规模是不会真正扩大的。然而分工的演进又受制于交易效率。在城镇化过程中,人口和产业不断聚集起来,可以极大地提高交易效率,促进分工深化和市场规模的扩展。在当前我国城镇化水平滞后的情况下,扩展市场、扩大内需的根本思路是要加快城镇化进程,进行社会经济结构的调整,促进农村地区的分工深化。     

中国居民代际收入流动性的变化趋势及影响机制研究

基于1989~2015年共计10轮CHNS数据,本文采用代际收入弹性和代际收入秩关联系数双重测度指标对我国居民代际收入流动性进行了测算,发现代际收入流动性在1991~2004年期间基本保持稳定,2004年以后呈现出不断上升的变化趋势。基于收入分组视角的研究发现,各收入组2004年以后代际收入阶层固化程度均有所降低,但高收入组和低收入组的固化程度远高于其他各组,中等收入群体是目前我国保持较高代际收入流动性的主要动力来源。从城乡差异视角看,受大规模农村劳动力向城镇流动的影响,2000年后农村家庭的代际流动性显著提升,且持续高于城市居民的代际流动性。进一步,基于人力资本分析框架对我国代际收入传递机制进行了探究,发现父亲的非教育因素在代际收入传递中起到主导作用。受整体社会制度环境不断改善的积极影响,2004年以后非教育传递机制不断减弱,对代际收入流动性的提升起到较大助推作用;而受高等教育扩张政策的影响,教育因素在2004年左右一定程度上削弱了代际收入流动性。