Ecological Influences on School Achievement in a Diverse Youth Sample: The Mediating Role of Substance Use

This study's purpose was to examine the extent to which closeness to family, peers, and school was associated with substance use and school achievement, based on the integrative model of ecological theory, social attachment theory, and social learning theory. A secondary data analysis was conducted on the first wave of the National Longitudinal Study of Adolescent Health (Add Health). The final sample yielded 3,147 boys and 3,356 girls.

A structural equation model was employed to test a hypothesized model. School closeness was found to be a primary ecological factor that significantly influenced school achievement while substance use emerged as a critical mediator of this relationship. Family closeness was negatively associated with school achievement. Also, substance use did not have a mediating function in the relationship between peer closeness and school achievement. No gender difference was found, except the relationship between family closeness and school achievement, in that family closeness had a significant, direct effect on school achievement among only boys but not girls.

The findings suggest that schools should strengthen adolescents' tie to school to promote their better academic success and to prevent them from substance use.     

An Ecological Approach to Understanding Youth Violence: The Mediating Role of Substance Use

The authors tested an ecological model that posits mediating variables (substance use and mental health) in the association between ecological factors (family closeness, school closeness, and peer closeness) and youth violence in a sample of 4,783 adolescents. Models including substance use present significantly less total effect between ecological factors and youth violence than do models without substance use. Additional probing of significant mediation effect using the Sobel test was performed and suggested that substance use did function as a mediator in the hypothesized path. Considerations of adolescent violence should recognize the possible role of ecological factors and how their influence may vary by substance use.     

Pitman closeness of record values from two sequences to population quantiles

Suppose upper records from two independent sequences from iid continuous random variables from the same distribution are observed. Pitman's measure of closeness of these statistics to population quantiles of the parent distribution is studied and various exact expressions are derived. For symmetric distributions, Pitman closeness probabilities of records to median are also obtained. Examples including exponential and uniform distributions are discussed. Numerical evaluations are presented to illustrate all the results developed here.     

平民化：城市广播新闻改革创新的新指向——宁波电台《新闻110》栏目有效探索

媒介的竞争核心说到底是内容资源的竞争,新闻平民化传播是广播媒介争取受众,赢得竞争的有效举措,是一项改革创新。在新闻实践中,宁波人民广播电台通过倾力打造民生服务类节目《新闻110》,提出了广播新闻平民化的途径和方法：在传播形态上,注重平民视角切入,贴近社会,贴近民众,强调与受众平等交流;在传播内容上,关注民生,为民众解疑释惑、排难解忧;在传播方式上,搭建与受众双向传播,互动参与平台,强调第一时间,第一现场。     

African American and Black Caribbean feelings of closeness to Africans

African American and Black Caribbean relations dominate research on interactions across black ethnic divides. Using National Survey of American Life data, we explore a different aspect of black interethnic attitudes: how close these groups feel towards Africans. African Americans and Black Caribbeans were largely similar in their feelings of closeness to Africans. For Black Caribbeans, younger and male respondents, those reporting higher levels of financial strain, living in the northeast and persons who immigrated to the US at least 11 years ago, report feeling especially close to Africans. Being male was the only significant correlate among African Americans. The findings are discussed in relation to how race, ethnicity and national origin shape personal identities within the US and their significance for intergroup perceptions. These broader issues warrant further consideration in light of assertions that race as a defining feature of American life and intergroup relations is obsolete.     

A Pitman measure of similarity in k-means for clustering heavy-tailed data

One of the most popular methods and algorithms to partition data to k clusters is k-means clustering algorithm. Since this method relies on some basic conditions such as, the existence of mean and finite variance, it is unsuitable for data that their variances are infinite such as data with heavy tailed distribution. Pitman Measure of Closeness (PMC) is a criterion to show how much an estimator is close to its parameter with respect to another estimator. In this article using PMC, based on k-means clustering, a new distance and clustering algorithm is developed for heavy tailed data.     

Mean likelihood estimators

The use of Mathematica in deriving mean likelihood estimators is discussed. Comparisons are made between the mean likelihood estimator, the maximum likelihood estimator, and the Bayes estimator based on a Jeffrey's noninformative prior. These estimators are compared using the mean-square error criterion and Pitman measure of closeness. In some cases it is possible, using Mathematica, to derive exact results for these criteria. Using Mathematica, simulation comparisons among the criteria can be made for any model for which we can readily obtain estimators.In the binomial and exponential distribution cases, these criteria are evaluated exactly. In the first-order moving-average model, analytical comparisons are possible only for n = 2. In general, we find that for the binomial distribution and the first-order moving-average time series model the mean likelihood estimator outperforms the maximum likelihood estimator and the Bayes estimator with a Jeffrey's noninformative prior. Mathematica was used for symbolic and numeric computations as well as for the graphical display of results. A Mathematica notebook which provides the Mathematica code used in this article is available: http://www.stats.uwo.ca/mcleod/epubs/mele. Our article concludes with our opinions and criticisms of the relative merits of some of the popular computing environments for statistics researchers.     

高校学报面临的困境及出路

高校学报面临着深刻的危机 ,社会效益和经济效益低下 ,普遍沦为评职称、考学位的工具。造成这种危机的根本原因在于高校学报内向性、封闭性和综合性的办刊模式。因此 ,实行开放办刊 ,走专业化的道路成为高校学报的必然选择。     

Pitman comparisons of predictors of censored observations from progressively censored samples for exponential distribution

On the basis of a progressively censored sample, Basak et al. [On some predictors of times to failure of censored items in progressively censored samples. Comput Statist Data Anal. 2006;50:1313 –1337] considered the problem of predicting the unobserved censored units at various stages of progressive censoring. They then discussed several different point predictors of these censored units and compared them with respect to mean square prediction error. In this work, we use the Pitman closeness (PC) criterion to compare the maximum likelihood, best linear unbiased, best linear equivariant, and conditional median predictors (CMPs) of these progressively censored units. Next, we compare all these with respect to the median unbiased predictor in terms of PC. Numerical computations are then performed to compare all these predictors. By comparing our results to those of Basak et al. (2006), we note that our findings in the sense of PC are similar to theirs in which the CMP competes well when compared to all other predictors.     

Pitman Closeness of kth Records Based on a Two-Sequence Case

Suppose upper kth records were observed from an X-sequence of iid continuous random variables, and kth upper records from another independent Y-sequence of iid variables from the same distribution are to be observed. The Pitman closeness probabilities of these statistics are derived. For symmetric distribution, the Pitman closeness probabilities of kth record statistics to the population median, are also examined and it is shown that these probabilities are distribution free. Numerical computations are conducted to illustrate the results developed here.