An Investigation of Event Study Methodologies with Clustered Events and Event Day Uncertainty

The specification and power of mean-adjusted, market and quadratic models in event studies using OLS, Patell, Jaffe and GLS are examined. Simulation is used with security and portfolio returns to capture different cross correlations. The market model is always superior in specification and power compared to the mean-adjusted and quadratic models. The use of OLS with the market model is supported in the absence of clustered events and event day uncertainty, whereas use of Jaffe with the market model is supported in the presence of these problems.     

Heteroskedasticity, autocorrelation, and spatial correlation robust inference in linear panel models with fixed-effects

This paper develops an asymptotic theory for test statistics in linear panel models that are robust to heteroskedasticity, autocorrelation and/or spatial correlation. Two classes of standard errors are analyzed. Both are based on nonparametric heteroskedasticity autocorrelation (HAC) covariance matrix estimators. The first class is based on averages of HAC estimators across individuals in the cross-section, i.e. “averages of HACs”. This class includes the well known cluster standard errors analyzed by Arellano (1987) as a special case. The second class is based on the HAC of cross-section averages and was proposed by Driscoll and Kraay (1998). The ”HAC of averages” standard errors are robust to heteroskedasticity, serial correlation and spatial correlation but weak dependence in the time dimension is required. The “averages of HACs” standard errors are robust to heteroskedasticity and serial correlation including the nonstationary case but they are not valid in the presence of spatial correlation. The main contribution of the paper is to develop a fixed-b asymptotic theory for statistics based on both classes of standard errors in models with individual and possibly time fixed-effects dummy variables. The asymptotics is carried out for large time sample sizes for both fixed and large cross-section sample sizes. Extensive simulations show that the fixed-b approximation is usually much better than the traditional normal or chi-square approximation especially for the Driscoll-Kraay standard errors. The use of fixed-b critical values will lead to more reliable inference in practice especially for tests of joint hypotheses.     

INTER-REGIONAL TRADE FLOW ESTIMATION THROUGH NON-SURVEY MODELS: AN EMPIRICAL ASSESSMENT

Inter-regional trade estimation has been pointed out as a crucial problem when constructing a multiregional input–output system. Knowledge of inter-regional trade flows, at least of the pooled volume of exports and imports by commodity, is critical in accounting for important spillover and feedback effects deriving from inter-regional linkages. However, in most countries, there are no completely reliable survey-based statistics on inter-regional trade. Thus, this paper intends to evaluate the reasonability of using indirect inter-regional trade estimates, comparing different estimating methods and assessing the sensitivity of the model results. Based on our empirical comparisons we conclude that input–output models are not greatly affected by the insertion of different trade values. Thus, our results support the use of indirect estimates for inter-regional trade, whenever survey-based data are unavailable.     

提高实践教学质量的机制探讨

在高等职业教育中,实践教学发展迅速,但还有不少地方需要进一步提高和完善。可通过建立增强“双师型”教师实践能力的拓展机制,建立校企互动、共建共赢的合作机制,建立实践性教材内容的升级更换机制,建立检验实践教学质量的考核评价机制,改进教学方法,不断提高实践教学的水平和质量。     

浅谈会计电算化条件下的审计

会计电算化信息系统的特点,使得审计工作面临新的困难。要解决这些困难,应改变审计线索、增加审计内容、更新审计技术、完善审计标准和准则、提高审计人员素质。