On the distribution of city sizes

The city size distribution in many countries is remarkably well described by a Pareto distribution. We derive conditions that standard urban models must satisfy in order to explain this regularity. We show that under general conditions urban models must have (i) a balanced growth path and (ii) a Pareto distribution for the underlying source of randomness. In particular, one of the following combinations can induce a Pareto distribution of city sizes: (i) preferences for different goods follow reflected random walks, and the elasticity of substitution between goods is 1; or (ii) total factor productivities of different goods follow reflected random walks, and increasing returns are equal across goods.     

Efficient tests for the presence of a pair of complex conjugate unit roots in real time series

We introduce a framework which allows us to draw a clear parallel between the test for the presence of seasonal unit roots and that for unit root at frequency 0 (or π$\pi$). It relies on the properties of the complex conjugate integrated of order one processes which are implicitly at work in the real time series. In the same framework as that of Phillips and Perron (Biometrica 75 (1988) 335), we derive tests for the presence of a pair of conjugate complex unit roots. The asymptotic distribution we obtain are formally close to those derived by these authors but expressed with complex Wiener processes. We then introduce sequences of near-integrated processes which allow us to study the local-to-unity asymptotic of the above test statistics. We state a result on the weak convergence of the partial sum of complex near-random walks which leads to complex Orstein–Uhlenbeck processes. Drawing on Elliott et al. (Econometrica 64 (1996) 813) we then study the design of point-optimal invariant test procedures and compute their envelope employing local-to-unity asymptotic approximations. This leads us to introduce new feasible and near efficient seasonal unit root tests. Their finite sample properties are investigated and compared with the different test procedures already available (J. Econometrics 44 (1991) 215; 62 (1994) 415; 85 (1998) 269) and those introduced in the first part of the paper.     

Unit root testing under a local break in trend

Recent approaches to testing for a unit root when uncertainty exists over the presence and timing of a trend break employ break detection methods, so that a with-break unit root test is used only if a break is detected by some auxiliary statistic. While these methods achieve near asymptotic efficiency in both fixed trend break and no trend break environments, in finite samples pronounced “valleys” in the power functions of the tests (when mapped as functions of the break magnitude) are observed, with power initially high for very small breaks, then decreasing as the break magnitude increases, before increasing again. In response to this problem, we propose two practical solutions, based either on the use of a with-break unit root test but with adaptive critical values, or on a union of rejections principle taken across with-break and without-break unit root tests. These new procedures are shown to offer improved reliability in terms of finite sample power. We also develop local limiting distribution theory for both the extant and the newly proposed unit root statistics, treating the trend break magnitude as local-to-zero. We show that this framework allows the asymptotic analysis to closely approximate the finite sample power valley phenomenon, thereby providing useful analytical insights.     

How useful are no-arbitrage restrictions for forecasting the term structure of interest rates?

We develop a general framework for analyzing the usefulness of imposing parameter restrictions on a forecasting model. We propose a measure of the usefulness of the restrictions that depends on the forecaster’s loss function and that could be time varying. We show how to conduct inference about this measure. The application of our methodology to analyzing the usefulness of no-arbitrage restrictions for forecasting the term structure of interest rates reveals that: (1) the restrictions have become less useful over time; (2) when using a statistical measure of accuracy, the restrictions are a useful way to reduce parameter estimation uncertainty, but are dominated by restrictions that do the same without using any theory; (3) when using an economic measure of accuracy, the no-arbitrage restrictions are no longer dominated by atheoretical restrictions, but for this to be true it is important that the restrictions incorporate a time-varying risk premium.     

A Study on the Productivities of IT Capital and Computer Labor: Firm-level Evidence from Taiwan’s Banking Industry

The current paper extends the non-neutral stochastic frontier production function—which belongs to the class of a one-step procedure as defined by Wang and Schmidt (2002) and developed by Huang and Liu (1994)—from a cross-sectional setting to a panel data modeling. Using a newly-surveyed dataset from Taiwan’s commercial banks on their investments in information and communication technologies (IT), I find that IT capital and computer labor tend to exhibit higher productivities than their non-IT and non-computer counterparts, that IT capital has positive impacts on the marginal productivities of computer labor and borrowed funds, and that the mean technical efficiency is around 87.7%. Evidence is found that the total factor productivity of the banking sector grew at an average rate of 0.28% per annum, albeit fluctuating, for the past 8 years.     

Estimation and testing of Euler equation models with time-varying reduced-form coefficients

This paper studies the estimation and testing of Euler equation models in the framework of the classical two-step minimum-distance method. The time-varying reduced-form model in the first step reflects the adaptation of private agents’ beliefs to the changing economic environment. The presumed ability of Euler conditions to deliver stable parameters indexing tastes and technology is interpreted as a time-invariant second-step model. This paper shows that, complementary to and independent of one another, both standard specification test and stability test are required for the evaluation of an Euler equation. As an empirical application, a widely used investment Euler equation is submitted to examination. The empirical outcomes appear to suggest that the standard investment model has not been a success for aggregate investment.     

Compilation of Input–Output Data from the National Accounts

In this paper, a new method is presented to derive an input–output table from a system of make and use tables. The method, which we call ‘activity technology’, is mathematically equivalent to the well-known commodity technology, but chooses another unit, i.e. the activity. We will argue that, in the activity technology model, negatives can only arise from causes such as heterogeneity and errors in the data. To apply the activity technology, very detailed make and use matrices are required, as well as additional data on the input structures of certain activities. We will describe a method that can incorporate this additional data within the activity technology framework. Statistics Netherlands has adopted the method     

基于移动通信技术的远程监控通信系统

现代化计算机科学的发展,使得网络化的信息系统成为可能。提出了一种基于移动通信技术的远程监控通信系统;构建了系统的基本框架,包括数据采集单元、数据传输单元和监控中心单位,各单元之间利用GSM短信服务实现远程通讯。利用该系统进行数据的远程传输与分析,可以大大提高数据利用率,保证监控对象的健康运转。     

Influence costs and hierarchy

In an internal capital market, individual departments may compete for a share of the firm’s budget by engaging in wasteful influence activities. We show that firms with more levels of hierarchy may experience lower influence costs than less hierarchical firms, even though the former provide more opportunities for exerting influence. The unique influence-cost minimizing hierarchy is strongly asymmetric. With a linear production technology this is also the optimal hierarchy. If individual departments have different productivities, however, and the production technology exhibits decreasing returns to scale, a symmetric hierarchy that does not minimize influence costs may be optimal.Received: July 2004, Accepted: October 2004, JEL Classification: D74, G31, G34We thank Martin Hellwig, seminar participants at the University of Mannheim, and an anonymous referee for helpful comments, and Kai Konrad for handling the editorial tasks on this paper. Financial support from Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 504 (Inderst and Müller) and the Bank of Sweden Tercentenary Foundation (Wärneryd) is gratefully acknowledged.     

A Unit Root Test Using a Fourier Series to Approximate Smooth Breaks*

We develop a unit‐root test based on a simple variant of Gallant's (1981) flexible Fourier form. The test relies on the fact that a series with several smooth structural breaks can often be approximated using the low frequency components of a Fourier expansion. Hence, it is possible to test for a unit root without having to model the precise form of the break. Our unit‐root test employing Fourier approximation has good size and power for the types of breaks often used in economic analysis. The appropriate use of the test is illustrated using several interest rate spreads.     

Further Evidence on the Statistical Properties of Real GNP*

The well‐known lack of power of unit‐root tests has often been attributed to the short length of macroeconomic variables and also to data‐generating processes (DGPs) departing from the I(1)–I(0) models. This paper shows that by using long spans of annual real gross national product (GNP) and GNP per capita (133 years), high power can be achieved, leading to the rejection of both the unit‐root and the trend‐stationary hypothesis. More flexible representations are then considered, namely, processes containing structural breaks (SB) and fractional orders of integration (FI). Economic justification for the presence of these features in GNP is provided. It is shown that both FI and SB formulations are in general preferred to the autoregressive integrated moving average (ARIMA) [I(1) or I(0)] formulations. As a novelty in this literature, new techniques are applied to discriminate between FI and SB. It turns out that the FI specification is preferred, implying that GNP and GNP per capita are non‐stationary, highly persistent but mean‐reverting series. Finally, it is shown that the results are robust when breaks in the deterministic component are allowed for in the FI model. Some macroeconomic implications of these findings are also discussed.     

Nonlinearities and Fractional Integration in the US Unemployment Rate*

This paper proposes a model of the US unemployment rate which accounts for both its asymmetry and its long memory. Our approach introduces fractional integration and nonlinearities simultaneously into the same framework, using a Lagrange multiplier procedure with a standard null‐limit distribution. The empirical results suggest that the US unemployment rate can be specified in terms of a fractionally integrated process, which interacts with some nonlinear functions of labour‐demand variables such as real oil prices and real interest rates. We also find evidence of a long‐memory component. Our results are consistent with a hysteresis model with path dependency rather than a non‐accelerating inflation rate of unemployment (NAIRU) model with an underlying unemployment equilibrium rate, thereby giving support to more activist stabilization policies. However, any suitable model should also include business cycle asymmetries, with implications for both forecasting and policy‐making.     

Nonlinear IV unit root tests in panels with cross-sectional dependency

We propose a unit root test for panels with cross-sectional dependency. We allow general dependency structure among the innovations that generate data for each of the cross-sectional units. Each unit may have different sample size, and therefore unbalanced panels are also permitted in our framework. Yet, the test is asymptotically normal, and does not require any tabulation of the critical values. Our test is based on nonlinear IV estimation of the usual augmented Dickey–Fuller type regression for each cross-sectional unit, using as instruments nonlinear transformations of the lagged levels. The actual test statistic is simply defined as a standardized sum of individual IV t-ratios. We show in the paper that such a standardized sum of individual IV t-ratios has limit normal distribution as long as the panels have large individual time series observations and are asymptotically balanced in a very weak sense. We may have the number of cross-sectional units arbitrarily small or large. In particular, the usual sequential asymptotics, upon which most of the available asymptotic theories for panel unit root models heavily rely, are not required. Finite sample performance of our test is examined via a set of simulations, and compared with those of other commonly used panel unit root tests. Our test generally performs better than the existing tests in terms of both finite sample sizes and powers. We apply our nonlinear IV method to test for the purchasing power parity hypothesis in panels.     

Methods for inference in large multiple-equation Markov-switching models

Inference for multiple-equation Markov-chain models raises a number of difficulties that are unlikely to appear in smaller models. Our framework allows for many regimes in the transition matrix, without letting the number of free parameters grow as the square as the number of regimes, but also without losing a convenient form for the posterior distribution. Calculation of marginal data densities is difficult in these high-dimensional models. This paper gives methods to overcome these difficulties, and explains why existing methods are unreliable. It makes suggestions for maximizing posterior density and initiating MCMC simulations that provide robustness against the complex likelihood shape.     

基于Feed4JUnit架构的单元测试技术研究与应用

软件测试技术在软件质量控制过程中一直起着非常重要的作用。JUnit是被广泛应用的Java单元测试框架,主要测试基于java语言编写的程序代码,用于编写和运行可重复的测试。Feed4JUnit是开源的基于JUnit的扩展,通过使用Feed4JUnit提供的注释,用户可以很方便地把测试数据存放在文件或其他数据源。本文分析了应用Feed4JUnit进行单元测试的方法,并通过实际开发示例实现数据与代码分离的测试。     

Vintage human capital and learning curves

I study a vintage-human-capital model in which long-lived workers accumulate human capital following an exogenous learning curve. Different skill levels inside a vintage are complementary in production; this makes the ex ante homogeneous workers enter different vintages. The continuous-time framework allows me to study the timing decision for the technology phase-out differentially and to derive sharp characterization for wages and the distribution of workers in the dying technology. I show how to posit and solve a planner's problem and construct equilibrium in this way. Consistent with empirical evidence, I show that the experience premium is always positive but diminishes as a technology ages. The connection between workers' learning curves and the technology's progress curve is characterized.     

运用项目信息系统 提升建筑企业的竞争力

文章指出建筑企业应充分利用信息技术所带来的巨大生产力,不断创新,其中包括利用项目信息系统(PIS)从多方面对企业的业务流程与管理方法、手段等进行重组和改革,进而提升建筑企业的竞争力,更好地求得生存和发展。     

A unified entropic pricing framework of option: Using Cressie-Read family of divergences

The entropy valuation of option (Stutzer, 1996) provides a risk-neutral probability distribution (RND) as the pricing measure by minimizing the Kullback–Leibler (KL) divergence between the empirical probability distribution and its risk-neutral counterpart. This article establishes a unified entropic framework by developing a class of generalized entropy pricing models based upon Cressie-Read (CR) family of divergences. The main contributions of this study are: (1) this unified framework can readily incorporate a set of informative risk-neutral moments (RNMs) of underlying return extracted from the option market which accurately captures the characteristics of the underlying distribution; (2) the classical KL-based entropy pricing model is extended to a unified entropic pricing framework upon a family of CR divergences. For each of the proposed models under the unified framework, the optimal RND is derived by employing the dual method. Simulations show that, compared to the true price, each model of the proposed family can produce high accuracy for option pricing. Meanwhile, the pricing biases among the models are different, and we hence conduct theoretical analysis and experimental investigations to explore the driving causes.     

柔性制造模式下参数化三维CAPP系统设计

面向多品种、小批量的柔性三维CAPP系统是先进制造中重要的单元技术。文章基于三维CAD/CAM平台技术,利用PLM技术研究三维CAPP系统的功能和结构特点,在采用特征知识描述形状结构和工艺信息的基础上,提出切实可行的三维CAPP系统框架,为三维产品并行设计与快速制造提供系统支撑技术。