Estimation of nonlinear errors-in-variables models: an approximate solution

We propose an easy to derive and simple to compute approximate least squares or maximum likelihood estimator for nonlinear errors-in-variables models that does not require the knowledge of the conditional density of the latent variables given the observables. Specific examples and Monte Carlo studies demonstrate that the bias of this approximate estimator is small even when the magnitude of the variance of measurement errors to the variance of measured covariates is large. Cheng Hsiao and Qing Wang's work was supported in part by National Science Foundation grant SeS91-22481 and SBR94-09540. Liqun Wang gratefully acknowledges the financial support from Swiss National Science Foundation. We wish to thank Professor H. Schneeweiss and a referee for helpful comments and suggestions.     

Building up adjusted indicators of students’ evaluation of university courses using generalized item response models

This article advances a proposal for building up adjusted composite indicators of the quality of university courses from students’ assessments. The flexible framework of Generalized Item Response Models is adopted here for controlling the sources of heterogeneity in the data structure that make evaluations across courses not directly comparable. Specifically, it allows us to: jointly model students’ ratings to the set of items which define the quality of university courses; explicitly consider the dimensionality of the items composing the evaluation form; evaluate and remove the effect of potential confounding factors which may affect students’ evaluation; model the intra-cluster variability at course level. The approach simultaneously deals with: (i) multilevel data structure; (ii) multidimensional latent trait; (iii) personal explanatory latent regression models. The paper pays attention to the potential of such a flexible approach in the analysis of students evaluation of university courses in order to explore both how the quality of the different aspects (teaching, management, etc.) is perceived by students and how to make meaningful comparisons across them on the basis of adjusted indicators.     

试析国资委经济增加值

现代企业财务管理正逐步转向价值创造和以价值最大化为基本目标。2010年初,国资委发布的《中央企业负责人经营业绩考核暂行办法》用经济增加值（EVA）指标取代了传统的净资产收益率（ROE）指标。经济增加值是价值总量指标,借助经济增加值的计算结果可以直接判断企业是否在为股东创造财富。在实际计算经济增加值时需要对利润和资本等项目进行调整。经济增加值考核指标有助于引导企业更加关注价值创造,提高企业可持续发展的能力。但是经济增加值考核指标仍然存在问题：行政规定的资本成本率影响经济增加值的准确性、可比性,影响企业对于项目风险的态度;经济增加值指标可能不利于鼓励企业进行长期投资;依然存在企业管理者利用各种盈余管理手段调节利润增加经济增加值的问题。     

A comment on approximating the x2 distribution in the equiprobable case

In an article appearing in this journal, Smith, et al. (1979) reported that a beta approximation of the X² distribution in the equiprobable case did not perform well. This brief note points out that they used the wrong moments and range in their approximation. It is suggested that when this problem is cor-rected, a beta approximation performs better than the chi-square or adjusted chi-square when k ≥ 3 and n is not too small.     

Multicovariate-adjusted regression models

We introduce multicovariate-adjusted regression (MCAR), an adjustment method for regression analysis, where both the response (Y) and predictors (X ₁, …, X _p ) are not directly observed. The available data have been contaminated by unknown functions of a set of observable distorting covariates, Z ₁, …, Z _s , in a multiplicative fashion. The proposed method substantially extends the current contaminated regression modelling capability, by allowing for multiple distorting covariate effects. MCAR is a flexible generalisation of the recently proposed covariate-adjusted regression method, an effective adjustment method in the presence of a single covariate, Z. For MCAR estimation, we establish a connection between the MCAR models and adaptive varying coefficient models. This connection leads to an adaptation of a hybrid backfitting estimation algorithm. Extensive simulations are used to study the performance and limitations of the proposed iterative estimation algorithm. In particular, the bias and mean square error of the proposed MCAR estimators are examined, relative to a baseline and a consistent benchmark estimator. The method is also illustrated with a Pima Indian diabetes data set, where the response and predictors are potentially contaminated by body mass index and triceps skin fold thickness. Both distorting covariates measure aspects of obesity, an important risk factor in type 2 diabetes.     

Comment on ‘An improved score interval with a modified midpoint for a binomial proportion’

Yu et al. [An improved score interval with a modified midpoint for a binomial proportion. J Stat Comput Simul. 2014;84:1022–1038] propose a novel confidence interval (CI) for a binomial proportion by modifying the midpoint of the score interval. This CI is competitive with the various commonly used methods. At the same time, Martín and Álvarez [Two-tailed asymptotic inferences for a proportion. J Appl Stat. 2014;41:1516–1529] analyse the performance of 29 asymptotic two-tailed CI for a proportion. The CI they selected is based on the arcsin transformation (when this is applied to the data increased by 0.5), although they also refer to the good behaviour of the classical methods of score and Agresti and Coull (which may be preferred in certain circumstances). The aim of this commentary is to compare the four methods referred to previously. The conclusion (for the classic error α of 5%) is that with a small sample size (≤80) the method that should be used is that of Yu et al.; for a large sample size (n?≥?100), the four methods perform in a similar way, with a slight advantage for the Agresti and Coull method. In any case the Agresti and Coull method does not perform badly and tends to be conservative. The program which determines these four intervals are available from the address http://www.ugr.es/local/bioest/Z_LINEAR_K.EXEhttp://www.ugr.es/local/bioest/Z_LINEAR_K.EXE.     

基于FrFT和子空间正交的LFM信号参数估计

基于分数阶Fourier变换和子空间正交性,提出了一种低信噪比下线性调频信号检测与参数估计方法。讨论过程中将线性调频信号通过适当的分数阶Fourier变换得到一个单频复正弦信号,在此基础上,利用信号子空间与噪声子空间的正交性处理其正弦信号,再对线性调频信号的检测和参数估计转化为函数极值求解;最后,利用计算机模拟证实了方法的有效性。     

Tests of heteroscedasticity and correlation in multivariate t regression models with AR and ARMA errors

Heteroscedasticity checking in regression analysis plays an important role in modelling. It is of great interest when random errors are correlated, including autocorrelated and partial autocorrelated errors. In this paper, we consider multivariate t linear regression models, and construct the score test for the case of AR(1) errors, and ARMA(s,d) errors. The asymptotic properties, including asymptotic chi-square and approximate powers under local alternatives of the score tests, are studied. Based on modified profile likelihood, the adjusted score test is also developed. The finite sample performance of the tests is investigated through Monte Carlo simulations, and also the tests are illustrated with two real data sets.     

亦谈净现值法与内含报酬率法冲突的协调

进行资本预算方案的对比与优选,是投资项目决策时经济可行性评价的关键。净现值法和内含报酬率法是决策者经常使用的两种经济评价方法,然而美中不足的是在对互斥方案进行决策时,两种方法有时会得出相互矛盾的结论。文章通过对这一矛盾产生的原因分析,提出了内含报酬率法的一种修正方法,不仅从理论上彻底解决了二者矛盾的问题,而且进行了实证研究。     

Three-level control charts with variable sample size,sampling interval,and control limits

Recently, three-level control chart has been developed for monitoring situations in which an appropriate quality measure uses three discrete levels to classify a product characteristic. In this paper, the variable parameters control charts for multinomial data are developed with a three-level classification scheme. We compare it with various adaptive charts to show that this modified scheme can improve the performance. In order to evaluate and compare the performance of this scheme, adjusted average time to signal is used as the performance measure. Results indicate that the proposed chart has improved performance and is relatively sensitive to small shifts.