Identifiable finite mixtures of location models for clustering mixed-mode data

For clustering mixed categorical and continuous data, Lawrence and Krzanowski (1996) proposed a finite mixture model in which component densities conform to the location model. In the graphical models literature the location model is known as the homogeneous Conditional Gaussian model. In this paper it is shown that their model is not identifiable without imposing additional restrictions. Specifically, for g groups and m locations, (g!)m–1 distinct sets of parameter values (not including permutations of the group mixing parameters) produce the same likelihood function. Excessive shrinkage of parameter estimates in a simulation experiment reported by Lawrence and Krzanowski (1996) is shown to be an artifact of the model's non-identifiability. Identifiable finite mixture models can be obtained by imposing restrictions on the conditional means of the continuous variables. These new identified models are assessed in simulation experiments. The conditional mean structure of the continuous variables in the restricted location mixture models is similar to that in the underlying variable mixture models proposed by Everitt (1988), but the restricted location mixture models are more computationally tractable.     

On perfect simulation for some mixtures of distributions

This paper studies the implementation of the coupling from the past (CFTP) method of Propp and Wilson (1996) in the set-up of two and three component mixtures with known components and unknown weights. We show that monotonicity structures can be exhibited in both cases, but that CFTP can still be costly for three component mixtures. We conclude with a simulation experiment exhibiting an almost perfect sampling scheme where we only consider a subset of the exhaustive set of starting values.     

早期酋长制群体的聚落形态比较研究——以内蒙古东部、安第斯山北部和美洲中部三个地区为例

对内蒙古东部、安第斯山北部和美洲中部三个地区的早期酋长制群体的聚落形态进 行的比较研究表明,尽管这三个地区的发展过程大致相当,但在这三个地区中,大体类似的转变 却以不同的方式发生,从而导致了三个各具特色的等级社会的出现。最初的、大规模的、以等级 制度原则组织起来的酋长制群体出现后,其发展轨道的早期阶段明显地为后来的、较大的、更复 杂的政治实体即国家的出现创造了条件。通过地域性聚落分析,可以发现这三个地区在不同规模 层次上的人口和社会组织的异同,其中在赤峰和奥哈卡(Oaxaca)地区都存在的小型群体却不见 于马格达雷那高地(AltoMagdalena)的现象,需要进行更深入的研究,才能进一步揭示出在马 格达雷那高地是什么样的社会交流把这些家庭联合成更大的社会团体。     

休闲与幸福:错综复杂的关系

幸福感概念构建在人具有主动性这一假定上,即人们若欲获得幸福,必须积极行动,唯有借助个人努力才可实现。幸福感亦为目标,一旦达成便可证明一个人整体的幸福。因此,我们愿意朝着幸福和良好的生活品质而努力这一事实,也更深刻地诠释了幸福的本质。另外,心理和社会的双重积极是幸福感的源泉。幸福的人总能积极地对待生活,不论眼前还是今后。休闲能够带来幸福,但休闲并非幸福本身。事实上,休闲是一种活动,是人们在空闲时间为了让生活变得更精彩、更有意义而做的事情。总体而言,我们如果因某种休闲活动而感到幸福,表明我们至少在一定程度上得到了满足。虽然休闲并不等同于幸福,但毋庸置疑,它对创造幸福至关重要。我们在休闲研究中绝不能忽略休闲与幸福这个当今生活中最具活力领域之间的联系,否则,我们将会丧失提升休闲与科学及公众之间关联性的机会。     

Bad news indeed for Ryff’s six-factor model of well-being

Springer and Hauser (An Assessment of the Construct Validity of Ryff’s Scales of Psychological Well-Being: Method, Mode, and Measurement Effects. 2006. Social Science Research 35) tested one key aspect of the validity of Ryff’s six-factor model of psychological well-being (RPWB), namely, whether there is substantial independent variation among the six factors. In several large and heterogeneous samples, under a variety of model specifications, and using various sets of RPWB items, we found very high factor correlations among the dimensions of well-being, especially personal growth, purpose in life, self-acceptance, and environmental mastery. That is, the six-factor model makes theoretical claims that do not yield large or consistent empirical distinctions when standard measures and instrumentation are used. Where Ryff and Singer’s comment (Best News Yet on the Six-Factor Model of Well-Being. 2006. Social Science Research 35) refers directly to that analysis, their methodological discussion is most often irrelevant or incorrect. Their text largely ignores and fails to challenge our strong empirical findings about the factorial structure of well-being. In this response, we reinforce these findings and their implications for the (in)validity of the six-factor well-being model as implemented by Ryff. We also explain why Ryff and Singer’s lengthy review of studies that show differential relationships of RPWB factors with other variables should be interpreted with far greater caution than Ryff and Singer recognize. We offer recommendations for analyzing RPWB items in surveys that have already been conducted, but we also emphasize the need for a thorough rethinking of the measurement and dimensionality of psychological well-being.     

创业投资:德国和美国的比较研究

在对美国和德国的创业投资的调查研究中,对照美国的研究结果,向德国的创业投资家调查了以下两个问题:1)在评估一项投资的时候创业投资家更看重创业者什么?2)根据一项创业投资计划,他们怎样与创业企业合作。调查结果显示,在创业的早期阶段和扩张阶段,德国创业投资家评估一项商业计划时,比较关注创业企业的发展潜力。他们强调,创业者所表现出的领导才能和对市场的熟悉程度是决定创业投资的必要条件。晚期阶段的创业投资家与早期阶段的创业投资家相比,不太容易和创业者成为亲密伙伴;他们对创业企业所提供的管理帮助也比较少。创业投资公司的规模在很大程度上影响创业投资的某些投资特征。与美国的研究结果相似,大规模的创业投资公司和小规模的创业投资公司运作的差异主要在于平均投资规模。在德国,随着创业投资公司规模的扩大,其投资的地域范围也在扩大。至于投资过程,当创业投资公司是主要投资者时,投资公司的规模与其所花费的评估和沟通时间(从开始与创业者接洽到进行融资之间)负相关。融资的准备时间与创业投资公司的员工数之间的关系,小规模的创业投资公司更有效率。     

Outsourcing to emerging markets: Theoretical perspectives and policy implications

Creating value through outsourcing has emerged as a popular competitive strategy for firms in various industries. In order to survive in the domestic and international marketplaces, firms, especially in developed countries, are seeking opportunities offshore, which is one focus of globalization. Offshore outsourcing has emerged as a popular competitive strategy and emerging markets have become increasingly attractive locations. As firms in developed countries (e.g., the US) continue to face enormous challenges to sustain competitive advantage, outsourcing to emerging markets is becoming an increasingly important source of business renewal and corporate transformation.In spite of the growing strategic significance of sourcing, we have limited knowledge of offshoring and outsourcing to emerging markets. The objectives of this review are fourfold: (1) to provide a better understanding of the concepts of offshoring and outsourcing business models, (2) to discuss relevant theoretical perspectives related to outsourcing, (3) to present a taxonomy of outsourcing strategies drawing on the extant literature, and (4) to discuss public policy implications. Conclusions and direction for future research are provided.     

A Comparative Pharmacokinetic Estimate of Mercury in U.S. Infants Following Yearly Exposures to Inactivated Influenza Vaccines Containing Thimerosal

The use of thimerosal preservative in childhood vaccines has been largely eliminated over the past decade in the United States because vaccines have been reformulated in single‐dose vials that do not require preservative. An exception is the inactivated influenza vaccines, which are formulated in both multidose vials requiring preservative and preservative‐free single‐dose vials. As part of an ongoing evaluation by USFDA of the safety of biologics throughout their lifecycle, the infant body burden of mercury following scheduled exposures to thimerosal preservative in inactivated influenza vaccines in the United States was estimated and compared to the infant body burden of mercury following daily exposures to dietary methylmercury at the reference dose established by the USEPA. Body burdens were estimated using kinetic parameters derived from experiments conducted in infant monkeys that were exposed episodically to thimerosal or MeHg at identical doses. We found that the body burden of mercury (AUC) in infants (including low birth weight) over the first 4.5 years of life following yearly exposures to thimerosal was two orders of magnitude lower than that estimated for exposures to the lowest regulatory threshold for MeHg over the same time period. In addition, peak body burdens of mercury following episodic exposures to thimerosal in this worst‐case analysis did not exceed the corresponding safe body burden of mercury from methylmercury at any time, even for low‐birth‐weight infants. Our pharmacokinetic analysis supports the acknowledged safety of thimerosal when used as a preservative at current levels in certain multidose infant vaccines in the United States.