Sensitivity analysis of efficiency rankings to distributional assumptions: applications to Japanese water utilities

This article examines the robustness of efficiency score rankings across four distributional assumptions for trans-log stochastic production-frontier models, using data from 1221 Japanese water utilities (for 2004 and 2005). One-sided error terms considered include the half-normal, truncated normal, exponential and gamma distributions. Results are compared for homoscedastic and doubly heteroscedastic models, where we also introduce a doubly heteroscedastic variable mean model, and examine the sensitivity of the nested models to a stronger heteroscedasticity correction for the one-sided error component. The results support three conclusions regarding the sensitivity of efficiency rankings to distributional assumptions. When four standard distributional assumptions are applied to a homoscedastic stochastic frontier model, the efficiency rankings are quite consistent. When those assumptions are applied to a doubly heteroscedastic stochastic frontier model, the efficiency rankings are consistent when proper and sufficient arguments for the variance functions are included in the model. When a more general model, like a variable mean model is estimated, efficiency rankings are quite sensitive to heteroscedasticity correction schemes.     

How should Engel's law be formulated?

Engel's law expresses a “negative stochastic association” of income and the proportion of income that is spent on food. However, there are many quite different notions of “negative stochastic association” and consequently there are different ways of defining Engel's law. We relate these different concepts to Engel's original statistical analysis and show that one must give credit to Engel for the first non-parametric statistical analysis of budget-data.     

中国商品期货市场的假日效应研究——基于收益和波动的视角

为研究中国商品期货市场假日效应的存在性及其特征,本文从收益和波动出发,在构建学生分布随机波动模型的基础上采用贝叶斯MCMC模拟技术对中国铜、铝、橡胶、大豆、豆粕和小麦期货市场的假日效应进行了实证分析,研究结果显示:假日前和假日后信息对商品期货交易收益及其波动均具有显著的影响,对不同交易品种而言,其影响方向及影响程度均存在一定差异;更具体地,对各类假日分别进行分析发现,元旦、春节、劳动节和国庆节的假日前和假日后信息对商品期货收益及其波动均具有显著的影响,且比分类之前假日前和假日后信息的影响能力明显增强,其个性特征也更加突出。     

我国上市公司的融资约束及其影响因素的实证分析

本文运用随机前沿计量分析方法,对我国上市公司的融资约束及其影响因素进行了实证研究。结果表明,融资约束在所研究的各行业是普遍存在的,且程度较为严重。在影响上市公司融资约束的因素中,国有控股公司相对非国有控股公司受到的融资约束程度要大,而股权的集中度与融资约束程度呈现出反向相关关系。同时结果显示,资本充足率越高、盈利能力越差的上市公司,受到的融资约束程度越大,而东部地区的上市公司受到的融资约束程度要小于中西部地区的上市公司。