农户对转基因技术的认知与采用行为分析——基于湖北与山东转基因抗虫棉种植的调查

根据湖北与山东两地实地调查获得的数据,分析了农户对转基因抗虫棉的认知与采用行为,考察农户对于转基因技术规则的认知和参与方式。研究表明,农户对转基因抗虫棉及其安全性、相关规则仍缺乏认知;农业技术人员仍然是农户获得种子信息的重要来源;由于经费严重不足和管理体制上的弊端,现有农技推广体系已经陷入困境,农民难以获得及时有效的种子技术方面的指导和服务;种子市场的监管不力及相关规则的缺乏,不但损害了农户的利益,而且加大了农户技术采用的风险。在此基础上提出了解农户的决策行为、制定合理完善的技术规则等促进转基因抗虫棉技术推广的相关建议。     

A Simplified Treatment of the Estimation of Parameters and Tests of Hypotheses in Constrained Design Models with Unbalanced Data

A simple approach to the least squares estimation of parameters in the linear design model is given. An algebraically tractable example for unbalanced data is used to illustrate the approach.     

A Parametric Test of Perfect Ranking in Balanced Ranked Set Sampling

Many techniques based on data which are drawn by Ranked Set Sampling (RSS) scheme assume that the ranking of observations is perfect. Therefore it is essential to develop some methods for testing this assumption. In this article, we propose a parametric location-scale free test for assessing the assumption of perfect ranking. The results of a simulation study in two special cases of normal and exponential distributions indicate that the proposed test performs well in comparison with its leading competitors.     

Testing for the maximum mean in a mixture of normals

We consider the test of the null hypothesis that the largest mean in a mixture of an unknown number of normal components is less than or equal to a given threshold. This test is motivated by the problem of assessing whether the Soviet Union has been operating in compliance with the Nuclear Test Ban Treaty. In our analysis, the number of normal components is determined using Akaike's Information Criterion while the hypothesis test itself is based on asymptotic results given by Behboodian for a mixture of two normal components. A bootstrap approach is also considered for estimating the standard error of the largest estimated mean. The performance of the testa are examined through the use of simulation.     

ESTIMATING PARAMETERS IN AUTOREGRESSIVE MODELS IN NON-NORMAL SITUATIONS: ASYMMETRIC INNOVATIONS

The estimation of coefficients in a simple autoregressive model is considered in a supposedly difficult situation where the innovations have an asymmetric distribution. Two distributions, gamma and generalized logistic, are considered for illustration. Closed form estimators are obtained and shown to be efficient and robust. Efficiencies of least squares estimators are evaluated and shown to be very low. This work is an extension of that of Tiku, Wong and Bian [1] Tiku, M. L., Wong, W. K. and Bian, G. 1999. Time Series Models with Asymmetric Innovations. Commun. Stat.-Theory Meth., 28: 1131–1160.  [Google Scholar] who give solutions for a simple AR(1) model.

     

Size and Power of Recent Tests for Homogeneity in Exponential Mixtures

The article investigates diagnostic procedures for finite mixture models. The problem is to decide whether given data stem from an exponential distribution or a finite mixture of such distributions. Recently, three new test approaches have been proposed, the modified likelihood ratio test (MLRT) by Chen et al. (2001 Chen , H. , Chen , J. , Kalbfleisch , J. D. ( 2001 ). A modified likelihood ratio test for homogeneity in finite mixture models . Journal of the Royal Statistical Society, B 63 : 19 – 29 .[Crossref] , [Google Scholar]), the ADDS test by Mosler and Seidel (2001 Mosler , K. , Seidel , W. ( 2001 ). Testing for homogeneity in an exponential mixture model . Australian and New Zealand Journal of Statistics 43 : 231 – 247 . [Google Scholar]), and the D-test by Charnigo and Sun (2004 Charnigo , R. , Sun , J. ( 2004 ). Testing homogeneity in a mixture distribution via the l ² distance between competing models . Journal of the American Statistical Society 99 : 488 – 498 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). The size and power of these tests are determined by Monte Carlo simulation and their relative merits are evaluated. We conclude that the ADDS test shows always not much less and under some alternatives, in particular lower contaminations, considerably more power than its competitors. Also, new tables for the ADDS test are provided.     

转型期的中国经济波动特征

本文使用1978-2013年的中国宏观经济数据,从总需求、产业、生产力、就业与工资、价格水平、货币与利息6个方面考察了改革开放以来我国经济波动的规律。不同于已有的研究结果,我们发现其具有明显的“转型经济”特征,主要体现在以下两个方面：一、经济周期大致可分为两个阶段：1978-1990年和1991-2013年。前一阶段,主要是供给面因素造成经济波动,且波动率较大。后一阶段,经济波动表现为需求驱动型,波动幅度明显减弱。二、第一产业就业人数与第二、三产业就业人数之和的比值具有明显的反周期特征。这反映了在我国的工业化进程中,农村剩余劳动力在空间上频繁迁移的特点,即宏观经济景气时,农村剩余劳动力迁移到城市;反之,则迁移回农村。     

基于LSTAR模型的中国股市泡沫风险识别

本文在非线性模型框架下拟合中国主要股价指数的真实数据生成过程,并提出股市泡沫风险识别方法,较Phillips et al.（2011）提出的上确界单位根(SADF)方法具备更好的效果,能够精准预判股市泡沫风险进而为防范化解金融风险的政策措施提供参考。实证检验发现,主要股价指数的波动均存在逻辑平滑转换自回归(LSTAR)模型描述的非线性特征,自推出以来,四大股价指数均存在泡沫风险,上证指数存在六个主要的持续期,深圳成指存在四个主要的持续期,沪深300指数存在两个主要持续期,而创业板指数存在三个持续期。总体来看,创业板指数的泡沫生成时间会先于其它三大指数,可以作为预警中国股票市场泡沫风险的先行指标,且2015年7月之后的中国股票市场并不存在泡沫风险。     

Improving dispersion tests by symmetrization

Comparing the variances of several independent samples is a classic problem and many tests have been proposed in the literature. Conover et al. [Conover, W.J., Johnson, M.E. and Johnson, M.M., 1981, A comparative study of tests for homogeneity of variances with applications to the outer continental self bidding data. Technometrics, 23, 351–361.] and Shoemaker [Shoemaker, L.H., 1995, Tests for difference in dispersion based on quantiles. The American Statistician, 49 (2), 179–182.] find that the existing tests lack power for skewed sampling distributions. To address this problem, we studied the effect of an a priori symmetrization of the data on the performance of tests for homogeneity of variances. This article also updates the comprehensive comparative study of Conover et al.