Estimating latent distributions in recurrent choice data

This paper introduces a flexible class of stochastic mixture models for the analysis and interpretation of individual differences in recurrent choice and other types of count data. These choice models are derived by specifying elements of the choice process at the individual level. Probability distributions are introduced to describe variations in the choice process among individuals and to obtain a representation of the aggregate choice behavior. Due to the explicit consideration of random effect sources, the choice models are parsimonious and readily interpretable. An easy to implement EM algorithm is presented for parameter estimation. Two applications illustrate the proposed approach.     

Additive and multiplicative models for gamma distributed random variables,and their application as psychometric models for response times

A class of models for gamma distributed random variables is presented. These models are shown to be more flexible than the classical linear models with respect to the structure that can be imposed on the expected value. In particular, both additive, multiplicative, and combined additive-multiplicative models can be formulated. As a special case, a class of psychometric models for reaction times is presented, together with their psychological interpretation. By means of a comparison with existing models, this class of models is shown to offer some possibilities that are not available in existing methods. Parameter estimation by means of maximum likelihood (ML) is shown to have some attractive properties, since the models belong to the exponential family. Then, the results of a simulation study of the bias in the ML estimates are presented. Finally, the application of these models is illustrated by an analysis of the data from a mental rotation experiment. This analysis is preceded by an evaluation of the appropriateness of the gamma distribution for these data.     

What Causes the Mean Bias of the Likelihood Ratio Statistic with Many Variables?

Abstract

Survey data often contain many variables. Structural equation modeling (SEM) is commonly used in analyzing such data. However, conventional SEM methods are not crafted to handle data with a large number of variables (p). A large p can cause T_ml, the most widely used likelihood ratio statistic, to depart drastically from the assumed chi-square distribution even with normally distributed data and a relatively large sample size N. A key element affecting this behavior of T_ml is its mean bias. The focus of this article is to determine the cause of the bias. To this end, empirical means of T_ml via Monte Carlo simulation are used to obtain the empirical bias. The most effective predictors of the mean bias are subsequently identified and their predictive utility examined. The results are further used to predict type I errors of T_ml. The article also illustrates how to use the obtained results to determine the required sample size for T_ml to behave reasonably well. A real data example is presented to show the effect of the mean bias on model inference as well as how to correct the bias in practice.     

题目难度分布和样本容量对两种CTT等值结果的影响

基于经典测验理论(CTT)的等值方法主要有线性等值和等百分位等值两种。在不同情境下,不同的等值方法会产生不同的等值结果。本研究以真分数等值为依据,用蒙特卡洛模拟研究方法,综合比较了各种题目难度分布条件下和各种样本容量条件下两种CTT等值方法的等值结果。研究结果表明:(1)线性等值的误差受题目难度分布影响较大,等百分位等值的误差几乎不受题目难度分布影响。(2)线性等值的误差几乎不受样本容量的影响,等百分位等值的误差受样本容量影响较大。(3)不论题目难度分布如何,只要样本容量足够大,等百分位等值的效果都比线性等值更好。     

工作记忆训练诱发的神经可塑性——基于系列fMRI实验的脑区分布递减时空模型

工作记忆训练(Working Memory Training, WMT)诱发神经可塑性, 但其具体机制尚不明晰。为探索WMT改变正常人群大脑功能的时空特性, 以“扩展的智力顶额整合理论”和“神经效率假说”为依据, 采用逐层递进的5种方法, 分6个步骤来查究近20年来正常人群WMT的37篇fMRI文献。第一步, 用叙述性综述、频数分析和卡方检验法比较脑区激活模式和脑网络功能连接在WMT前后发生的改变, 发现WMT改变了大脑的5个联合区、7个宏观区和3个子区。其中, 额上回、顶下小叶和扣带回这3个子区各自激活减弱的报道文献数量多于其激活增强的, 且这种差异分别具有统计学意义。第二步, 采用激活似然估计法对其中26篇开展元分析, 发现大脑的3个子区激活减弱水平在WMT前后的差异具有统计学意义, 即额中回(BA6和8)、额上回(BA6)和前扣带回(BA24和32)。第三步, 综合定性和定量分析结果, 提出WMT脑区分布递减时空模型, 产生5个结果和讨论。第四步, 采用非参数检验进一步追踪WMT效应的调节因素, 发现训练的任务类型和时间分别对脑区激活的影响具有统计学意义。第五步, 针对正常人群WMT诱发神经可塑性的时空特性, 得出3个结论：第一, WMT改变了正常人群相应脑区的神经活动, 表现为减弱或增强, 但减弱更加突出, 且更新和较短时间的WMT倾向于诱发较多减弱; 第二, 这些神经活动变化主要发生在额顶叶联合区, 但也包括分别以颞叶、枕叶、扣带回及纹状体为主的联合区, 在一定范围内体现了整脑功能联合。这体现了WMT诱发神经可塑性的空间特性, 且符合“扩展的智力顶额整合理论”; 第三, 额中回、额上回、顶下小叶和扣带回(尤其前扣带回)这4个子区在激活减弱水平上重点展示了WMT神经可塑性的时间特性, 且符合“神经效率假说”, 恰好体现出“聪明的大脑更懒惰”。第六步, 指出WMT诱发神经可塑性的未来研究可能关注脑可塑性中的低活跃性、辨析额中回、额上回、顶下小叶和扣带回(尤其前扣带回)这4个子区在激活减弱水平上体现的时间特性、找寻训练减弱或增强大脑活动的综合性影响因素。     

True Context‐dependent Preferences? The Causes of Market‐dependent Valuations

A central assumption of neoclassical economics is that reservation prices for familiar products express people's true preferences for these products; that is, they represent the total benefit that a good confers to the consumers and are, thus, independent of actual prices in the market. Nevertheless, a vast amount of research has shown that valuations can be sensitive to other salient prices, particularly when individuals are explicitly anchored on them. In this paper, the authors extend previous research on single‐price anchoring and study the sensitivity of valuations to the distribution of prices found for a product in the market. In addition, they examine its possible causes. They find that market‐dependent valuations cannot be fully explained by rational inferences consumers draw about a product's value and are unlikely to be fully explained by true market‐dependent preferences. Rather, the market dependence of valuations likely reflects consumers' focus on something other than the total benefit that the product confers to them. Furthermore, this paper shows that market‐dependent valuations persist when – as in many real‐life settings – individuals make repeated purchase decisions over time and infer the distribution of the product's prices from their market experience. Finally, the authors consider the implications of their findings for marketers and consumers. Copyright © 2013 John Wiley & Sons, Ltd.     

我国乡镇卫生资源二次配置模式探讨

长期以来,我国卫生资源配置城乡不均衡的局面比较严峻,大量优质卫生资源主要积聚在大中城市,而乡镇基层医疗机构的卫生资源比较稀缺。以增加政府财政投入,引入私人资本与第三部门力量等方式来提高农村卫生资源增量势必会遇到投入缓慢、资金不足、技术瓶颈等现实障碍。通过改革公立医院,调整城市卫生资源存量,把大中城市公立医院中的富余卫生资源以二次配置方式转移到农村卫生服务机构,是破解农村卫生资源存量不足、增长缓慢的困境,提高农村卫生服务能力和水平,改善农民就医问药问题的新途径。     

红细胞体积分布宽度与冠心病关系的研究近况

红细胞体积分布宽度是血常规检测报告的一部分,临床多用于各种贫血的诊断与鉴别诊断。近年国内外研究显示,其测量值的增高与冠心病的死亡等不良事件发生风险增加密切相关。本文对其生物学特性与检测原理、与冠心病关系、测量值的增高预测冠心病不良预后的可能机制的研究进行综述。