禽保健促产中药添加剂对蛋鸡产蛋力的影响

通过对50至60周龄罗曼鸡进行试验,发现保健促产中草药添加剂能提高蛋鸡的产蛋力。与对照组相比,产蛋率提高2．44％,蛋重增加1．4g,平均每只母鸡试验期产蛋1．494kg,比对照组多产0．162kg,增产12．162％,破壳率降低0．52％,蛋壳厚度增加0．0392mm,有显著性差异,P＜0．05。表明该添加剂确有促进蛋鸡产蛋力的作用。     

On a criticism of the profile likelihood function

The profile likelihood function is often criticized for giving strange or unintuitive results. In the cases discussed here these are due to the use of density functions that have singularities. These singularities are naturally inherited by the profile likelihood function. It is therefore apparently important to be reminded that likelihood functions are proportional to probability functions, and so cannot have singularities. When this issue is addressed, then the profile likelihood poses no problems of this sort. This is of particular importance since the profile likelihood is a commonly used method for dealing with separate estimation of parameters.     

Formal adult education and socioeconomic inequality: Second chances or Matthew Effects?

In countries around the world, population aging, technological change, and labor market transformations are leading to an increasing incidence of mismatch between the skills and credentials held by workers and those required by their jobs. This is leading large numbers of people to return to schooling to enhance their prospects in the workplace. Access to adult education is highly stratified, and the returns to educational re-entry vary across social categories. This state-of-the-art paper focuses on two aspects. First, it examines the degree to which adult education (specifically, degree-bearing education) most benefits the less advantaged and thus mitigates socioeconomic inequality (second chance effects). Second, it addresses the degree to which the benefits of adult education go primarily to those who are already advantaged (Matthew Effects). Our review adopts the perspective of the socioeconomic life course and is explicitly cross-nationally comparative.     

Unit-Root Tests and Asymmetric Adjustment With an Example Using the Term Structure of Interest Rates

This article develops critical values to test the null hypothesis of a unit root against the alternative of stationarity with asymmetric adjustment. Specific attention is paid to threshold and momentum threshold autoregressive processes. The standard Dickey–Fuller tests emerge as a special case. Within a reasonable range of adjustment parameters, the power of the new tests is shown to be greater than that of the corresponding Dickey–Fuller test. The use of the tests is illustrated using the term structure of interest rates. It is shown that the movements toward the long-run equilibrium relationship are best estimated as an asymmetric process.     

The impact of sense of coherence and high-demand/low-control job environment on self-reported health,burnout and psychophysiological stress indicators

Sense of Coherence (SOC) is a new concept belonging to a salutogenic paradigm, proposing to explain health as contrasted to disease, a pathogenic paradigm. The Job Demand-Control (JDC) model of job stress suggests that the combination of high job demands and low job control, defined as job strain, is strongly associated with adverse health consequences. The aim of this study was to evaluate the relationship between SOC and the JDC model in assessment of negative job effects within three pathogenically defined contexts: self-reported health, burnout and psychophysiological stress indicators, assessing the explanatory value of SOC for such variables. The study was conducted with 103 employees of social-welfare and social-insurance agencies in Sweden. A questionnaire related to job conditions, health and burnout was administered, and blood samples were collected and analysed for serum concentrations of cortisol, prolactin and immunoglobulin G. Multiple-regression models were calculated including variables from all three contexts. In the analyses, a distinction was made between emotional job strain and quantitative job strain. The SOC interacted with emotional job strain, but the interaction also increased the independent effect of emotional job strain. The independent effect of SOC disappeared in most models when interaction was included. It is concluded that studies of job strain-effects according to the JDC model should include the SOC as an interaction factor.     

产业结构升级对城乡收入差距的门槛效应分析

综合借鉴前人的研究成果,本文将产业结构升级、城镇化进程和城乡收入差距三者联系起来,初步判断产业结构升级对城乡收入差距的影响是非线性的;然后采用2005-2018年我国省级面板数据,以城镇化率为门槛变量,对此进行了实证检验。结果显示:产业结构升级与城乡收入差距之间存在明显的非线性关系,前者对后者的影响具有显著的双门槛效应,当城镇化水平处于初级阶段时,产业结构合理化和高级化扩大了城乡收入差距;当城镇化水平越过第一门槛值进入中级阶段后,产业结构合理化的影响减弱为不显著,而产业结构高级化仍在显著扩大城乡收入差距;当城镇化水平越过第二门槛值进入高级阶段后,产业结构合理化和高级化都表现为显著缩小城乡收入差距。通过剔除样本中的极端值、替换被解释变量和核心解释变量的代理变量,进行稳健性检验,上述结论依然成立。另外,分地区来看,东部、东北和西部地区的产业结构升级对城乡收入差距的影响同样存在显著的双门槛效应,但不同区域的表现不尽相同,东部和东北地区的门槛效应均表现为倒“U”型;西部地区则“慢半拍”,尚处于倒“U”型曲线的左侧;中部地区则仅存在以城镇化率为门槛变量的单门槛效应。文章分析了其中的原 因,并给出了政策含义。     

Is There a Jump in the Transition?

This article develops a statistical test for the presence of a jump in an otherwise smooth transition process. In this testing, the null model is a threshold regression and the alternative model is a smooth transition model. We propose a quasi-Gaussian likelihood ratio statistic and provide its asymptotic distribution, which is defined as the maximum of a two parameter Gaussian process with a nonzero bias term. Asymptotic critical values can be tabulated and depend on the transition function employed. A simulation method to compute empirical critical values is also developed. Finite-sample performance of the test is assessed via Monte Carlo simulations. The test is applied to investigate the dynamics of racial segregation within cities across the United States.     

Simplified hierarchical linear models for the evaluation of surrogate endpoints

The linear mixed-effects model (Verbeke and Molenberghs, 2000) has become a standard tool for the analysis of continuous hierarchical data such as, for example, repeated measures or data from meta-analyses. However, in certain situations the model does pose insurmountable computational problems. Precisely this has been the experience of Buyse et al. (2000a) who proposed an estimation- and prediction-based approach for evaluating surrogate endpoints. Their approach requires fitting linear mixed models to data from several clinical trials. In doing so, these authors built on the earlier, single-trial based, work by Prentice (1989), Freedman et al. (1992), and Buyse and Molenberghs (1998). While Buyse et al. (2000a) claim their approach has a number of advantages over the classical single-trial methods, a solution needs to be found for the computational complexity of the corresponding linear mixed model. In this paper, we propose and study a number of possible simplifications. This is done by means of a simulation study and by applying the various strategies to data from three clinical studies: Pharmacological Therapy for Macular Degeneration Study Group (1977), Ovarian Cancer Meta-analysis Project (1991) and Corfu-A Study Group (1995).     

Inferring the Predictability Induced by a Persistent Regressor in a Predictive Threshold Model

We develop tests for detecting possibly episodic predictability induced by a persistent predictor. Our framework is that of a predictive regression model with threshold effects and our goal is to develop operational and easily implementable inferences when one does not wish to impose à priori restrictions on the parameters of the model other than the slopes corresponding to the persistent predictor. Differently put our tests for the null hypothesis of no predictability against threshold predictability remain valid without the need to know whether the remaining parameters of the model are characterized by threshold effects or not (e.g., shifting versus nonshifting intercepts). One interesting feature of our setting is that our test statistics remain unaffected by whether some nuisance parameters are identified or not. We subsequently apply our methodology to the predictability of aggregate stock returns with valuation ratios and document a robust countercyclicality in the ability of some valuation ratios to predict returns in addition to highlighting a strong sensitivity of predictability based results to the time period under consideration.     

A class of mixed models for recurrent event data

In this article, we propose a class of mixed models for recurrent event data. The new models include the proportional rates model and Box–Cox transformation rates models as special cases, and allow the effects of covariates on the rate functions of counting processes to be proportional or convergent. For inference on the model parameters, estimating equation approaches are developed. The asymptotic properties of the resulting estimators are established and the finite sample performance of the proposed procedure is evaluated through simulation studies. A real example with data taken from a clinic study on chronic granulomatous disease (CGD) is also illustrated for the use of the proposed methodology. The Canadian Journal of Statistics 39: 578–590; 2011. © 2011 Statistical Society of Canada