Approximate estimation in nonlinear panel data models

This paper is concerned with the estimation of a general class of nonlinear panel data models in which the conditional distribution of the dependent variable and the distribution of the heterogeneity factors are arbitrary. In general, exact analytical results for this problem do not exist. Here, Laplace and small-sigma appriximations for the marginal likelihood are presented. The computation of the MLE from both approximations is straightforward. It is shown that the accuracy of the Laplace approximation depends on both the sample size and the variance of the individual effects, whereas the accuracy of the small-sigma approximation is 0(1) with respect to the sample size. The results are applied to count, duration and probit panel data models. The accuracy of the approximations is evaluated through a Monte Carlo simulation experiment. The approximations are also applied in an analysis of youth unemployment in Australia.     

Computational and statistical efficiency of semiparametric gls estimators

In this note, we report a dramatic improvement in the computational efficiency of semiparametric generalized least squares(SGLS) estimation. Computation of SGLS estimates no longer presents serious problems with data sets of moderate size. We also correct a numerical error in the standard errors of the SGLS estimates reported in our recent paper in this journal (Horowitz and Neumann, 1987). The corrected standard errors of SGLS are comparable to those we reported for quantile estimates.     

武夷山风景名胜区外围保护地带规划初探

以武夷山风景名胜区为例,阐述和分析了我国风景名胜区外围保护地带的发展现状,并概括其内涵,深刻解读了武夷山风景名胜区外围保护地带规划的背景;同时,针对其复杂的背景和外部情况,对其外围保护地带提出了分区规划的思想,分别对溪东国家旅游度假区保护地带、九曲溪上游水源保护地带和一般外围保护地带等3个分区提出了各自对应的保护内容和规划策略;并在此基础上为其制定了有效的保护和管理措施,为武夷山风景名胜区构建了一个系统、可行、操作性强的外围保护地带规划。     

基于凸度缺口模型的商业银行利率风险最优控制及其应用

对商业银行利率风险的管理和控制,传统的久期模型仅适用于利率变化较小和利率期限结构平移条件下的线性近似估计,否则就需要运用凸度进行调整。根据Markowitz现代组合投资理论,构造一个目标规划模型,通过合理确定其中决策变量的值,使商业银行在决策期末满足最小化利率风险和银行资产负债组合的凸度为非负的条件下收益最大化。计算实例表明,凸度缺口模型对于给定的初始值和约束条件,可以较好地减少利率风险的暴露头寸和提高收益;同时,利率风险较大时凸度缺口模型比久期缺口模型更好地减少风险暴露,鲁棒性(robustness)更强。     

时距认知的年龄差异

年龄是影响时距认知的一个重要因素.基于时间认知的信息加工模型,通过对时距估计和时距辨别两种任务条件下的有关年龄差异研究的回顾,发现虽然相关的研究结果没有确定的结论,但年老被试在时距加工的准确性和变异性上与年轻被试存在显著的差异.由于研究中所采用的时距长度、任务不同,内部时钟频率、注意和记忆都可能导致时距认知上的年龄差异.现代脑成像技术可为研究时距认知年龄差异的机制提供有效的手段.     

新化方言的动态助词

新化方言的动态助词可以表示起始态、持续态、完成态、经历态和尝试态等语法范畴 ,本文全面描写新化方言动态助词的意义和用法     

Exploring Parameter Relations for Multi‐Stage Models in Stage‐Wise Constant and Time Dependent Hazard Rates

Single cohort stage‐frequency data are considered when assessing the stage reached by individuals through destructive sampling. For this type of data, when all hazard rates are assumed constant and equal, Laplace transform methods have been applied in the past to estimate the parameters in each stage‐duration distribution and the overall hazard rates. If hazard rates are not all equal, estimating stage‐duration parameters using Laplace transform methods becomes complex. In this paper, two new models are proposed to estimate stage‐dependent maturation parameters using Laplace transform methods where non‐trivial hazard rates apply. The first model encompasses hazard rates that are constant within each stage but vary between stages. The second model encompasses time‐dependent hazard rates within stages. Moreover, this paper introduces a method for estimating the hazard rate in each stage for the stage‐wise constant hazard rates model. This work presents methods that could be used in specific types of laboratory studies, but the main motivation is to explore the relationships between stage maturation parameters that, in future work, could be exploited in applying Bayesian approaches. The application of the methodology in each model is evaluated using simulated data in order to illustrate the structure of these models.     

Working to get fired? Unemployment benefits and employment duration

In many countries, jobseekers are entitled to unemployment benefits (UBs) only if they have previously worked a minimum period of time. This institutional feature creates a sharp change in the disutility from unemployment at UB eligibility and may distort the duration of jobs. In this paper, we evaluate this eligibility effect using a regression discontinuity approach. Our evidence is based on longitudinal social security data from Portugal, where jobseekers are required to work a relatively long period to collect UBs. We find that monthly transitions from employment to unemployment increase by 10% as soon as the eligibility condition is met. This result is driven entirely by transitions to subsidised unemployment, which increase by 20%, as non-subsidised unemployment is not affected. The effects are even larger for the unemployed with high UB replacement ratios or those who meet the eligibility condition from multiple short employment spells. These transitions deserve greater attention from UB agencies and public employment services.     

Factors associated with early cessation of breastfeeding in women with gestational diabetes mellitus

AimTo determine factors associated with early cessation of breastfeeding (≤3 months) in women with recent gestational diabetes mellitus (GDM).MethodsA cross-sectional online survey of women aged ≥18 years, diagnosed with GDM in 2010 and registered with the National Diabetes Services Scheme in Australia. The 59 questions examined breastfeeding duration, intention, attitudes, exclusivity and support.Results738 women completed the survey (15% response rate). Data was analysed for 729 eligible respondents. Of these 97% reported ‘ever’ breastfeeding and 19% had breastfed for ≤3 months. Cessation of breastfeeding at or before 3 months was associated with breastfeeding problems at home [adjusted odds ratio 8.01, 95% confidence interval (4.57, 14.05)], return to work prior to three months [OR 3.39 (95% CI 1.53, 7.55)], inadequate breastfeeding support [OR 1.88 (95% CI 1.10, 3.22)], caesarean delivery [OR 1.70 (95% CI 1.04, 2.76)], low socioeconomic status (SEIFA 1 unit increase) [OR 0.89 (95% CI 0.81, 0.97)] and BMI (2 unit increase) [OR 1.08 (95% CI 1.01, 1.57)]. Being married or de facto [OR 0.14 (95% CI 0.03, 0.62)] was a protective against early cessation of breastfeeding.ConclusionStrategies to improve breastfeeding duration in women with GDM need to address those most at risk of early cessation and provide appropriate postpartum breastfeeding support in this group.     

Mixture inverse Gaussian for unobserved heterogeneity in the autoregressive conditional duration model

In this paper, we assume that the duration of a process has two different intrinsic components or phases which are independent. The first is the time it takes for a trade to be initiated in the market (for example, the time during which agents obtain knowledge about the market in which they are operating and accumulate information, which is coherent with Brownian motion) and the second is the subsequent time required for the trade to develop into a complete duration. Of course, if the first time is zero then the trade is initiated immediately and no initial knowledge is required. If we assume a specific compound Bernoulli distribution for the first time and an inverse Gaussian distribution for the second, the resulting convolution model has a mixture of an inverse Gaussian distribution with its reciprocal, which allows us to specify and test the unobserved heterogeneity in the autoregressive conditional duration (ACD) model.

Our proposals make it possible not only to capture various density shapes of the durations but also easily to accommodate the behaviour of the tail of the distribution and the non monotonic hazard function. The proposed model is easy to fit and characterizes the behaviour of the conditional durations reasonably well in terms of statistical criteria based on point and density forecasts.