Using principal components to test normality of high-dimensional data

Many multivariate statistical procedures are based on the assumption of normality and different approaches have been proposed for testing this assumption. The vast majority of these tests, however, are exclusively designed for cases when the sample size n is larger than the dimension of the variable p, and the null distributions of their test statistics are usually derived under the asymptotic case when p is fixed and n increases. In this article, a test that utilizes principal components to test for nonnormality is proposed for cases when p/n → c. The power and size of the test are examined through Monte Carlo simulations, and it is argued that the test remains well behaved and consistent against most nonnormal distributions under this type of asymptotics.     

从《一去永不回》看两性视野中女性成长的困境与突围

女性主义文学的成长是女性从被遮蔽、扭曲到发出自己的声音的一个不平凡的过程。池莉的《一去永不回》展示了一个平凡的女性从沉默到爆发,从不自觉走向半自觉的心路历程,以人物成长的外部语境和内心自我辨认来展示两性视野中女性成长的困境与突围,检视在社会环境和文化压力的重负下,女性意识究竟以何种面目生长和呈现。     

Accurate Response with Refurbished Consumer Returns

Centering around anticipative and reactive capabilities of firms, accurate response is an important supply‐side strategy to deal with demand uncertainty. Clearly, the structure of the possible reaction will crucially influence the optimal anticipative decision making. In this article, we extend the existing literature in this area by including a new reactive capability, namely the utilization of refurbished consumer returns from early sales to react to demand later in the selling season. Because consumer returns depend on previous sales, there is also a direct link to the anticipative supply decision. We capture this effect in a newsvendor‐type model and provide both analytical and numerical insights into the optimal anticipative and reactive decisions as well as the value of refurbishing in terms of the retailer's expected profitability.     

Alleviating linear ecological bias and optimal design with subsample data

Summary.  We illustrate that combining ecological data with subsample data in situations in which a linear model is appropriate provides two main benefits. First, by including the individual level subsample data, the biases that are associated with linear ecological inference can be eliminated. Second, available ecological data can be used to design optimal subsampling schemes that maximize information about parameters. We present an application of this methodology to the classic problem of estimating the effect of a college degree on wages, showing that small, optimally chosen subsamples can be combined with ecological data to generate precise estimates relative to a simple random subsample.     

Learning from experience or learning from others?: Inferring informal training from a human capital earnings function with matched employer–employee data

A model of informal training which combines learning from own experience and learning from others is proposed in this paper. It yields a closed-form solution that revises Mincer–Jovanovic's [Mincer, J., Jovanovic, B., 1981. Labor mobility and wages. In: Rosen, S. (Ed.), Studies in Labor Markets. Chicago University Press, Chicago, pp. 21–64] treatment of tenure in the human capital earnings function. We estimate the structural parameters of this non-linear model on a large French cross-section with matched employer–employee data. We find that workers on average can learn from others 10% of their own human capital on entering one plant, and catch half of their learning from others’ potential in just 2 years. The private marginal returns to education are declining with education as more educated workers have less to learn from others and share the social returns of their own education with their less qualified co-workers. The potential for learning from others on the job varies across jobs and establishments, and this provides a new distinction between imitation jobs and experience jobs. Workers in imitation jobs, who learn most from others, tend to have considerably longer tenure than workers in experience jobs. Although workers in experience jobs can learn little from others, we find that they learn a lot by themselves. We document several analogies between the imitation jobs/experience jobs “dualism” and the primary/secondary jobs and firms’ dualism implied by the dual labor market theory. However, our binary classification of jobs depicts the data more closely than the dual theory categorization into primary-type and secondary-type establishments. Competition prevails between jobs and firms but jobs differ by their learning technology.     

The increasing unemployment gap between the low and high educated in West Germany. Structural or cyclical crowding-out?

This paper addresses trends in education-specific unemployment risks at labor market entry in West Germany from the mid-1970s to the present. In line with previous research it shows that vocationally qualified school-leavers have relatively lower unemployment risks than school-leavers with general education. Over time, the gap in unemployment risks between the low-educated and medium- and highly educated labor market entrants substantially widened for both sexes. The literature identifies two different mechanisms for this trend: structural or cyclical crowding out. While in the former scenario low-educated become increasingly unemployed due to an oversupply of tertiary graduates and displacement from above, in the latter their relative unemployment risk varies with the business cycle. The results provide evidence for cyclical rather than structural crowding-out in West Germany. Since macroeconomic conditions became generally worse over time, this strongly explains the widening unemployment gap between the low-educated and all other education groups.     

Partial orders with respect to continuous covariates and tests for the proportional hazards model

Several omnibus tests of the proportional hazards assumption have been proposed in the literature. In the two-sample case, tests have also been developed against ordered alternatives like monotone hazard ratio and monotone ratio of cumulative hazards. Here we propose a natural extension of these partial orders to the case of continuous and potentially time varying covariates, and develop tests for the proportional hazards assumption against such ordered alternatives. The work is motivated by applications in biomedicine and economics where covariate effects often decay over lifetime. The proposed tests do not make restrictive assumptions on the underlying regression model, and are applicable in the presence of time varying covariates, multiple covariates and frailty. Small sample performance and an application to real data highlight the use of the framework and methodology to identify and model the nature of departures from proportionality.     

Heterogeneity in returns to college education: selection bias in contemporary taiwan

The causal impact of higher education on earnings may be heterogeneous across different members of a population. Using a newly developed instrumental-variable method in economics, we illustrate heterogeneous treatment effects of higher education on earnings resulting from sorting mechanisms that select individuals with certain unobserved attributes into college education. The setting of our empirical work is contemporary Taiwan - a transitional economy that has recently experienced a rapid expansion in higher education. We find distinct patterns by gender, with selection bias most clearly shown among women but not among men: the college return to earnings is on average greater for women who actually attended college than women who did not attend college.     

入世后中国外贸增长特点与增长方式的转变

中国加入WTO后,对外贸易连续三年超高速增长。这种增长势头与外部需求和国内宏观经济背景显然都有联系,特别是外贸增长方式的转变密不可分。转变外贸增长方式是实现中国2010年远景目标的关键。