On Rates of Convergence for Bayesian Density Estimation

Abstract.  We consider the problem of estimating a compactly supported density taking a Bayesian nonparametric approach. We define a Dirichlet mixture prior that, while selecting piecewise constant densities, has full support on the Hellinger metric space of all commonly dominated probability measures on a known bounded interval. We derive pointwise rates of convergence for the posterior expected density by studying the speed at which the posterior mass accumulates on shrinking Hellinger neighbourhoods of the sampling density. If the data are sampled from a strictly positive, α -Hölderian density, with α  ∈ ( 0,1] , then the optimal convergence rate n^{− α / (2 α +1)} is obtained up to a logarithmic factor. Smoothing histograms by polygons, a continuous piecewise linear estimator is obtained that for twice continuously differentiable, strictly positive densities satisfying boundary conditions attains a rate comparable up to a logarithmic factor to the convergence rate n ^−4/5 for integrated mean squared error of kernel type density estimators.     

On an adaptive version of the Metropolis–Hastings algorithm with independent proposal distribution

In this paper, we present a general formulation of an algorithm, the adaptive independent chain (AIC), that was introduced in a special context in Gåsemyr et al . [ Methodol. Comput. Appl. Probab. 3 (2001)]. The algorithm aims at producing samples from a specific target distribution Π, and is an adaptive, non-Markovian version of the Metropolis–Hastings independent chain. A certain parametric class of possible proposal distributions is fixed, and the parameters of the proposal distribution are updated periodically on the basis of the recent history of the chain, thereby obtaining proposals that get ever closer to Π. We show that under certain conditions, the algorithm produces an exact sample from Π in a finite number of iterations, and hence that it converges to Π. We also present another adaptive algorithm, the componentwise adaptive independent chain (CAIC), which may be an alternative in particular in high dimensions. The CAIC may be regarded as an adaptive approximation to the Gibbs sampler updating parametric approximations to the conditionals of Π.     

Confidence Intervals for Current Status Data

Abstract.  The likelihood ratio statistic for testing pointwise hypotheses about the survival time distribution in the current status model can be inverted to yield confidence intervals (CIs). One advantage of this procedure is that CIs can be formed without estimating the unknown parameters that figure in the asymptotic distribution of the maximum likelihood estimator (MLE) of the distribution function. We discuss the likelihood ratio-based CIs for the distribution function and the quantile function and compare these intervals to several different intervals based on the MLE. The quantiles of the limiting distribution of the MLE are estimated using various methods including parametric fitting, kernel smoothing and subsampling techniques. Comparisons are carried out both for simulated data and on a data set involving time to immunization against rubella. The comparisons indicate that the likelihood ratio-based intervals are preferable from several perspectives.     

网络时代农产品质量安全事件风险放大机制研究——基于价值累加理论的扎根分析

随着互联网的飞速发展,农产品质量安全事件借助网络媒体持续关联与聚合、发酵与扩散,极大地影响着公众的情感和态度,易引发集体非理性恐慌,网络时代信息扩散和迭代呈现全新特征和趋势,故加强农产品质量安全事件风险放大机制研究具有重要意义。基于斯梅尔塞的价值累加理论,结合“土坑酸菜”事件,利用Python技术获取媒体原始资料,对资料进行扎根编码分析,构建农产品质量安全事件风险放大机制模型。根据编码结果识别出农产品质量安全事件风险放大六大主范畴,包括结构性诱因、结构性紧张、一般化信念、(有效的)组织动员、社会控制、风险放大,将主范畴内容纳入价值累加理论六大因素中,分析表明农产品质量安全事件风险放大是以突发事件为分界点,分为前期蓄势、中期造势、紧急处理三个阶段,前期蓄势和中期造势阶段通过多轮循环相互反馈影响,最终放大农产品质量安全事件风险。在整个风险扩散过程中,网络是农产品质量安全事件风险的“社会放大站”,其加速了信息传播,强化了公众风险感知。本研究运用价值累加理论、基于宏观和微观整合层面,细化探究了网络时代农产品质量安全事件风险放大的完整过程机制,进一步完善了风险放大SARF研究框架,为相关研究做了有益补充。     

电商参与会促进农户农产品质量认证吗?——基于黄土高原苹果优势产区农户的分析

作为数字经济新业态的农产品电子商务成为促进农业高质量发展的有效途径。基于黄土高原苹果优势产区农户实地调研数据,使用多维固定效应模型分析电商参与对农户农产品质量认证的影响;利用中介效应模型和KHB方法剖析电商参与促进农户农产品质量认证的作用机制。研究结果表明:电商参与能够显著提升农户农产品质量认证的概率,同时增加了多重质量认证的可能;参与电商通过提高农户农产品质量认证意愿、增加农产品市场信息以及促进农产品品牌建设三个途径影响农产品质量认证。在此基础上,提出应加强农村信息基础设施建设与电商技术培训,提高农产品质量认证和品牌推广等对策,以此促进农户进行农产品质量认证,实现农业高质量发展。     

新旧世界葡萄酒质量表达演变及形成

葡萄酒等级是全球葡萄酒行业的关注点。在旧世界葡萄酒等级表达中,产品等级不仅反映产品内在质量,还与具有质量风格的地理特征紧密相关;新世界葡萄酒等级表达中,葡萄酒地理特征仅表示产品来源真实性,葡萄酒质量以产品口感为基础并满足消费者消费偏好需求。葡萄酒官方等级分级具有从产区到列级酒庄的纵向化结构,葡萄酒等级分类具有从品种、年份到酒庄的横向化结构,前者分级以生产者视角下“为何分级”并同时聚焦分级内生形成关键要素,后者分类以消费者视角下“为何分类”并锚定产品质量的某一关键要素,两者之间关注点存在差异。这种差异给国际葡萄酒市场创造竞争空间,形成一种质量表达的实践共创、智慧共存的竞争格局。     

青海话中的词缀"头"

青海话中的词缀“头”除了有与汉语普通话词缀“头”相同的特点外,还能够放在动词词根和形容词词根语素的后面,构成一个新的名词,表示某事是否值得做或必要性的主观评价,也可以指对象或状态;这种方式构成的名词是一个开放的系统,只存在于具体语境之中。文章还进一步探讨了这种用法的起源,并与其它方言中的词缀“头”作了对比分析。     

家庭环境对幼儿学习品质发展的影响——基于34项实证研究的元分析

学习品质是帮助幼儿获得积极学业成就的内在机制,家庭环境是影响幼儿学习品质发展的重要因素。为了深入探究幼儿学习品质与家庭因素之间的关系,本研究运用CMA3.7软件对34项实证研究的相关文献进行元分析。研究结果显示,幼儿学习品质与家庭因素呈现显著正相关。不同学习品质纬度与家庭因素的相关程度存在差异。从高到低排序为：想象与创造、坚持与专注、反思与解释、主动性、好奇心与兴趣。具体而言,家庭经济条件、父母参与程度以及家庭投入与支持对幼儿学习品质发展有显著影响。此外,性别与年龄对幼儿学习品质不同纬度的发展水平具有显著调节效应。主要教育建议：家长应在幼儿学习品质发展的关键时期给予关注,重视与幼儿的亲子互动,提高家庭支持和投入力度,并根据幼儿的个性特点有针对性地培养,从而促进其学习品质均衡发展。     

Examining Localized Patterns of Air Quality Perception in Texas: A Spatial and Statistical Analysis

Environmental and human health issues associated with outdoor air pollution, such as ozone, sulfur dioxide, and other pollutants in metropolitan regions, are an area of growing concern for both policy officials and the general public. Increasing attention from the news media, new health data, and public debate over the effectiveness of clean air regulations have raised the importance of air quality in the public consciousness. While public perceptions of air quality have been studied thoroughly dating back to the 1960s, little empirical research has been conducted to explain the spatial aspects of these perceptions, particularly at the local level. Although recent studies suggest characteristics of local setting are important in shaping perceptions of air quality, the roles of proximity, neighborhood characteristics, and location have not been clarified. This study seeks to improve understanding of the major factors shaping public perceptions of air quality by examining the spatial pattern of local risk perception, the role of socioeconomic characteristics in forming these perceptions, and the relationship between perceived and scientifically measured air pollution. First, we map the spatial pattern of local air quality perceptions using Geographic Information Systems (GIS) across the Dallas and Houston metropolitan areas. Next, we explain these perceptions through local contextual factors using both bivariate correlations and multivariate regression analysis. Results indicate that perceptions of air quality in the study areas are not significantly correlated with air quality based on readings of air monitoring stations. Instead, perceptions appear to be influenced by setting (urban vs. rural), state identification, access to information, and socioeconomic characteristics such as age, race, and political identification. We discuss the implications of the findings and provide direction on how further research can provide a deeper understanding of the local contextual factors influencing public perceptions.     

试论继续教育对教师素质的现代转换

继续教育是我国为实现现代化尤其是教育现代化、人的现代化所进行的新型教育。本文从知识经济与教育现代化的背景上论述了继续教育对教师素质进行转换的必要性、基本内涵、基本内容以及转换的方向。