新型农业经营主体的经营绩效与差异分析——基于农村固定观察点的数据调查

新型农业经营主体的经营绩效关系到其可持续发展。采用农村固定观察点对我国各省区新型农业经营主体的调查数据,运用随机前沿分析法,对不同类型的经营主体的经营绩效进行分析,并进一步分析新型农业经营主体的差异性。结果表明：相比小农户而言,新型农业经营主体的经营绩效相对较高,但是其平均绩效还有很大的改善空间;新型农业经营主体面临融资难和人才缺乏的问题,且该问题在农民专业合作社中最为突出;我国家庭农场的经营绩效在三种新型农业经营主体中是最高的,其次是农业（龙头）企业,最后是农民专业合作社。对此,提出应完善土地“三权分置”机制,实现新型农业经营主体的规模化生产,进一步解决其融资难和人才缺乏的问题,加大政策扶持力度等建议。     

北朝《李骞墓志》考释

李骞是北朝赵郡李氏代表人物之一。近年来《李骞墓志》的发现,为研究其生平以及赵郡李氏的有关问题提供了新史料。结合墓志和相关史料可知,李骞原名希义,字景让,后改名骞,再改字希义;李骞家族原来聚居平棘,后来迁居柏仁;李骞庶长兄长钧未被记入《李骞墓志》,李骞长女宝信当为高延宗妃;李骞生于北魏宣武帝永平元年(公元508年),卒于东魏孝静帝武定七年(公元549年),曾在北魏和东魏担任多种官职;《李骞墓志》出土于河北省赞皇县。     

Bias correction for parameter estimates of spatial point process models

When a spatial point process model is fitted to spatial point pattern data using standard software, the parameter estimates are typically biased. Contrary to folklore, the bias does not reflect weaknesses of the underlying mathematical methods, but is mainly due to the effects of discretization of the spatial domain. We investigate two approaches to correcting the bias: a Newton–Raphson-type correction and Richardson extrapolation. In simulation experiments, Richardson extrapolation performs best.     

Infill asymptotics for adaptive kernel estimators of spatial intensity

We apply the Abramson principle to define adaptive kernel estimators for the intensity function of a spatial point process. We derive asymptotic expansions for the bias and variance under the regime that n independent copies of a simple point process in Euclidean space are superposed. The method is illustrated by means of a simple example and applied to tornado data.     

The precision of regression-type estimator for incremental cost–effectiveness ratio

The estimation of incremental cost–effectiveness ratio (ICER) has received increasing attention recently. It is expressed in terms of the ratio of the change in costs of a therapeutic intervention to the change in the effects of the intervention. Despite the intuitive interpretation of ICER as an additional cost per additional benefit unit, it is a challenge to estimate the distribution of a ratio of two stochastically dependent distributions. A vast literature regarding the statistical methods of ICER has developed in the past two decades, but none of these methods provide an unbiased estimator. Here, to obtain the unbiased estimator of the cost–effectiveness ratio (CER), the zero intercept of the bivariate normal regression is assumed. In equal sample sizes, the Iman–Conover algorithm is applied to construct the desired variance–covariance matrix of two random bivariate samples, and the estimation then follows the same approach as CER to obtain the unbiased estimator of ICER. The bootstrapping method with the Iman–Conover algorithm is employed for unequal sample sizes. Simulation experiments are conducted to evaluate the proposed method. The regression-type estimator performs overwhelmingly better than the sample mean estimator in terms of mean squared error in all cases.     

论夜间搜查——从两则案例谈起

由于我国《刑事诉讼法》对搜查的时间未作规定,导致司法实践中夜间搜查频繁出现。夜间搜查很容易侵犯被搜查人和与其同住的人的隐私权和生活安宁权,给其造成伤害,司法实践中也确实发生了因夜间搜查而把人吓病的案例。因此,我国在再次修改《刑事诉讼法》时应规定禁止夜间搜查。当然,在保护公民隐私权和生活安宁权的同时,也要兼顾打击犯罪的需要,法律可以设置一些禁止夜间搜查的例外。     

Bayesian analysis of multivariate stochastic volatility with skew return distribution

Multivariate stochastic volatility models with skew distributions are proposed. Exploiting Cholesky stochastic volatility modeling, univariate stochastic volatility processes with leverage effect and generalized hyperbolic skew t-distributions are embedded to multivariate analysis with time-varying correlations. Bayesian modeling allows this approach to provide parsimonious skew structure and to easily scale up for high-dimensional problem. Analyses of daily stock returns are illustrated. Empirical results show that the time-varying correlations and the sparse skew structure contribute to improved prediction performance and Value-at-Risk forecasts.     

Monte carlo estimates of the distributions of the random polygons of the voronoi tessellation with respect to a poisson process

A large-scale study, in which two million random Voronoi polygons (with respect to a homogeneous Poisson point process) were generated and mensurated, is described. The polygon characteristics recorded are number of sides (or vertices), perimeter, area and interior angles. A feature is the efficient “quantile” method of replicating Poisson-type random structures, which it is hoped may find useful application elsewhere.     

Piecewise FARIMA models for long-memory time series

We consider the problem of modelling a long-memory time series using piecewise fractional autoregressive integrated moving average processes. The number as well as the locations of structural break points (BPs) and the parameters of each regime are assumed to be unknown. A four-step procedure is proposed to find out the BPs and to estimate the parameters of each regime. Its effectiveness is shown by Monte Carlo simulations and an application to real traffic data modelling is considered.