Cohomology, Symmetry, and Perfection

One of the aims of this paper is to better explain the philosophy behind the computations in [E.Bifet, C.De Concini,C.Procesi Cohomology of Regular Embeddings ] and to place them in a wider conceptual setting. Another aim of the paper is to outline in the last section an ``equivariant'' approach to some key results in the theory of toric varieties. The text of the first three sections follows closely a talk delivered at the University of Copenhagen in July 1989 on the occasion of the Zeuthen Symposium. This paper is dedicated to the memory of my friend Pere Menal and will appear in the Fall 1992 issue, dedicated to his memory, of Publicacions Matem\`atiques, Universitat Aut\`onoma de Barcelona.Comment: 11 pages, AmS-TeX 2.

Linear least squares estimation of the first order moving average parameter

We propose an iterative procedure to minimize the sum of squares function which avoids the nonlinear nature of estimating the first order moving average parameter and provides a closed form of the estimator. The asymptotic properties of the method are discussed and the consistency of the linear least squares estimator is proved for the invertible case. We perform various Monte Carlo experiments in order to compare the sample properties of the linear least squares estimator with its nonlinear counterpart for the conditional and unconditional cases. Some examples are also discussed- En aquest document de treball es proposa un procediment iteratiu per minimitzar la suma de quadrats dels errors que evita la naturalesa no lineal de l¿estimació del paràmetre del model mitjana mòbil de primer ordre i proporciona una expressió de l¿estimador en forma tancada. A continuació es discuteixen les propietats asimptòtiques del mètode i es demostra la consistència de l¿estimador per mínims quadrats lineals per a valors del paràmetre dins l¿interval obert (¡1; 1) : També es duen a terme diversos experiments de Monte Carlo per tal de comparar les propietats mostrals de ¿estimador per mínims quadrats lineals amb el seu homòleg no lineal pel cas condicional i pel no condicional. Finalment, es discuteixen alguns exemple

SENSITIVITY ANALYSIS OF EFFICIENCY AND MALMQUIST PRODUCTIVITY INDICES: AN APPLICATION TO SPANISH SAVINGS BANKS

Hypothesis testing and statistical precision in the context of nonparametric efficiency and productivity measurement have been investigated since the early 1990s. Recent contributions focus on this matter through the use of resampling methods?i.e., bootstrapping techniques. However, empirical evidence is still practically non-existent. This gap is more noticeable in the case of banking efficiency studies, where the literature is immense. In this paper, we explore productivity growth and productive efficiency for Spanish savings banks over the (initial) post-deregulation period 1992?1998 using Data Envelopment Analysis (DEA) and bootstrapping techniques. Results show that productivity growth has occurred, mainly due to improvement in production possibilities, and that mean efficiency has remained fairly constant over time. The bootstrap analysis yields further evidence, as for many firms productivity growth, or decline, is not statistically significant. With regard to efficiency measurement, the bootstrap reveals that the disparities in the original efficiency scores of some firms are lessened to a great extent. Desde principios de los años noventa ha habido avances notables en el contraste de hipótesis dentro del contexto de la medición de la eficiencia y la productividad mediante técnicas paramétricas. Las contribuciones más recientes han enfocado el tema a través de métodos de remuestreo -conocidos en la literatura como técnicas bootstrap-. Sin embargo, prácticamente no ha habido aplicaciones, algo también patente en el estudio de la eficiencia de la empresa bancaria. En este artículo, analizamos la eficiencia productiva y el crecimiento de la productividad de las cajas de ahorro españolas durante el periodo 1992-1998 a través de técnicas no paramétricas (DEA) y de técnicas bootstrap, con el fin de poder realizar inferencia estadística. Los resultados indican que la productividad ha aumentado, principalmente debido a una mejora en las posibilidades de producción, mientras que la eficiencia promedio no ha variado sustancialmente. El análisis bootstrap revela que, en el caso de la productividad, para muchas empresas su aumento o disminución no es estadísticamente significativo. En cuanto a la eficiencia, muestra que las diferencias entre empresas individuales se reducen de manera notable cuando consideramos intervalos de confianza.bootstrap, data envelopment analysis, efficiency, productivity, savings bank bootstrap, técnicas no paramétricas, eficiencia, productividad, cajas de ahorro.

Linear least squares estimation of the first order moving average parameter

We propose an iterative procedure to minimize the sum of squares function which avoids the nonlinear nature of estimating the rst order moving average parameter and provides a closed form of the estimator. The asymptotic properties of the method are discussed and the consistency of the linear least squares estimator is proved for the invertible case. We perform various Monte Carlo experiments in order to compare the sample properties of the linear least squares estimator with its nonlinear counterpart for the conditional and unconditional cases. Some examples are also discussed.nonlinear optimization, monte carlo simulation in time series, invertible models, moving average processes, consistent estimator

The Role of Public Service Broadcasters in the Era of Convergence A Case Study of Televisió de Catalunya

The development of the convergence process has several implications in the reconfiguration of the media landscape. Public services broadcasters have new opportunities to fulfil their public service duties in a new competitive environment, which involves developing new applications on new platforms. Televisió de Catalunya, the public service broadcaster (PSB) of Catalonia, has developed a clear strategy in this new convergent environment, applying its traditional know-how to new interactive and digital media according to its public mission and getting positive feedback.convergence; public service broadcasting; interactive TV; bandwidth; 3G services; multimedia and digital divide