A Comparison of Some Recent Bayesian and Classical Procedures for Simultaneous Equation Models with Weak Instruments

We compare the finite sample performance of a number of Bayesian and Classical procedures for limited information simultaneous equations models with weak instruments by a Monte Carlo study. We consider recent Bayesian approaches developed by Ch ao and Phillips (1998, CP), Geweke (1996), Kleibergen and van Dijk (1998, KVD), and Zellner (1998). Amongst the Sample theory methods, OLS, 2SLS, LIML, Fuller's modified LIML, and the jackknife instrumental variable estimator (JIVE) due to Angrist, Imben s and Krueger (1999) and Blomquist and Dahlberg (1999) are also considered. Since the posterior densities and their conditionals in CP and KVD are non-standard, we propose a ''Gibbs within Metropolis-Hastings'' algorithm, which only requires the availabi lity of the conditional densities from the candidate generating density. Our results show that in cases with very weak instruments, there is no single estimator that is superior to others in all cases. When endogeneity is weak, Zellner's MELO does the best. When the endogeneity is not weak and $\rho$$w_{12}>0$, where $\rho$ is the correlation coefficient between the structural and reduced form errors, and $w_{12}$ is the covariance between the unrestricted reduced form errors, BMOM outp erforms all other estimators by a wide margin. When the endogeneity is not weak and $\beta \rho

A Comparison of Some Recent Bayesian and Classical Procedures for Simultaneous Equation Models with Weak Instruments

We compare the finite sample performance of a number of Bayesian and classical procedures for limited information simultaneous equations models with weak instruments by a Monte Carlo study. We consider recent Bayesian approaches developed by Chao and Phillips (1998, CP), Geweke (1996), Kleibergen and van Dijk (1998, KVD), and Zellner (1998). Amongst the sampling theory methods, OLS, 2SLS, LIML, Fuller's modified LIML, and the jackknife instrumental variable estimator (JIVE) due to Angrist, Imbens and Krueger (1999) and Blomquist and Dahlberg (1999) are also considered. Since the posterior densities and their conditionals in CP and KVD are non-standard, we propose a "Gibbs within Metropolis- Hastings" algorithm, which only requires the availability of the conditional densities from the candidate generating density. Our results show that in cases with very weak instruments, there is no single estimator that is superior to others in all cases. When endogeneity is weak, Zellner's MELO does the best. When the endogeneity is not weak and rw > 0, where r is the correlation coefficient between the structural and reduced form errors, and w is the co-variance between the unrestricted reduced form errors, BMOM outperforms all other estimators by a wide margin. When the endogeneity is not weak and brLimited Information Estimation, Metropolis-Hastings Algorithm, Gibbs Sampler, Monte Carlo Method

Effects of soil hydraulic properties on simulated hydrological response generated by LISEM 5.0

[Abstract] LISEM model (Limburg Soil Erosion Model) is actually being developped in order to perform dynamic simulations of surface runoff and erosion in catchments. This model is also proposed as analysis support system for soil erosion problems derived from agricultural management practices, which can be used as a kernel of an expert system for agricultural and environmental planning. Hydrological response of LISEM 5.0 is analysed on the basis of soil water flow parameter values of the Green-Ampt sub-model, which estimates infiltration rates. Observed hydrographs in the stream gauge installed in a catchment were tested with those simulated by LISEM 5.0. Observed hydrographs shows that the hydrological response of experimental catchment corresponds to a variable source type. By contrast, given the assumptions of LISEM 5.0 for calculating runoff , the calculated hydrological response is always hortonian.Results showed that, for any set of infiltration parameters, Green-Ampt infiltration submodel is not able to simulate the observed streamflow discharge (variable source). This occurs because the rainfall intensity-infiltration ratii do not allow a generalized hortonian surface runoff as predicted by LISEM 5.0. Hortonian runoff only may be possible at short times and limited to small areas, and does not appear to be significant in the observed hydrographs

Development of an improved method for soil and water conservation planning at catchment scale in the East African Higlands : Progress Report 1 jan - 30 sep 2002

The overall goal of the EROAHI Project is to improve the Catchment Approach, a methodology for participatory soil conservation planning currently applied in the East African Highlands Eco-region. Anticipated improvements are: semi-quantification of soil and productivity loss using farmers’ knowledge, simple ex ante economic cost-benefit analysis of proposed scenarios and moving up the SWC planning from farm level to catchment scale. The project goal is to be achieved by realising the following objectives (EROAHI Management Document 1, 2000): To develop field-scale indicators of erosion and sedimentation based on indigenous knowledge of soil and vegetation characteristics; 1. To attach quantitative values of erosion, sedimentation and/or productivity to the developed indicators, based on field scale measurements; 2. To quantify erosion, sedimentation and soil productivity at catchment scale using the developed indicators and compare the estimates with a detailed model study to develop simple 'rules of thumb' for erosion assessment; 3. To develop a methodology for economic impact assessment of planned soil and water conservation measures at farm level; 4. To further develop a specific methodology for catchment scale soil and water conservation planning in the East African Highlands using a participatory approach

The Tools and Equipment for a Bending of Tubes

Bakalářská práce je zaměřena na vytvoření všeobecného přehledu používaných přípravků a zařízení pro ohýbání trubek. Na základě literární studie byl dále vytvořen přehled základních metod používaných pro ohyb trubek. Provedením průzkumu výrobních programů výrobců strojů pro ohýbání trubek byly popsány jednotlivé principy metod, které jsou doplněny příslušnou obrázkovou dokumentací. Ke každé metodě bylo uvedeno několik příkladů výrobců zařízení. Přiložená obrázková dokumentace názorně ukazuje konstrukci jednotlivých strojů a použité přípravky.The bachelor thesis is aimed to make a general overview of used tools and equipment for a bending of tubes. On the basis of literary evidence the list of basic methods used in bending tubes was created. By conducting a survey in bending tubes producers manufacturing programs, various principles of bending tubes were described, which are supplemented with picture documentation. To each method there were mentioned some of the OEMs. Accompanying pictures describe the construction of individual machines and used tools and equipment.

Simulation of erosion risk in an agricultural catchment with LISEM model: influence of tilling direction and agronomic measurements

[Abstract] Results of a series of simulations made in an agricultural catchment in A Coruña using LISEM model are shown. We tried to assess the influence that exert over the runoff and the soil loss factors such as tilling direction, wheeltracks systems, use of grass strips, increasing of random roughness or the increase of hydraulic conductivity. To define the simulated scenarios we used morphologic data of the catchment and supposed refered to plot distribution and land uses as well as input parameters, experimental and bibliographical. In all cases, they were simulated with precipitations with a return period of 2 and 25 years. Under these conditions we estimated that the runoff risk is associated, fundamentally, to intense precipitation events. This risk tend to increase when, as a consequence of tilling, soil infiltration capacity is reduced. Other factors, as tilling direction and wheeltracks systems, influence, more or less, in the magnitude of the runoff produced in a small agricultural catchment

Uso de un modelo basado en eventos para evaluar la conductividad hidráulica en una cuenca de pequeñas dimensiones

Los suelos de cultivo situados en pendiente y desarrollados sobre esquistos del Complejo de Órdenes en Galicia, se consideran sensibles a la acción de la escorrentía y a la erosión hídrica. Ello se debe al efecto conjunto de un clima húmedo con precipitaciones elevadas durante la estación invernal, a suelos de textura franca o franco-limosa que pueden encostrarse y a la topografía ondulada. Para luchar eficazmente en contra de los efectos adversos de la erosión y la escorrentía es importante conocer aquellos períodos de la estación húmeda en que la intensidad de la infiltración es de menor cuantía, en ausencia de cubierta vegetal. En este contexto se utilizó un modelo determinista con base física (LISEM), que funciona asociado a un SIG de tipo raster (PCRaster), para predecir la erosión y la escorrentía. Mediante el modelo LISEM se estimó la conductividad hidráulica a saturación (Ks) en una pequeña cuenca agrícola mediante el método de prueba y error, usando datos de precipitación y caudal. Las series de datos experimentales corresponden a ocho eventos medidos en la cuenca de 10,7 ha denominada Abelar durante el período 1997/1998. Dado que LISEM requiere una cantidad importante de parámetros de entrada, se utilizaron diferentes fuentes de información para obtener estos datos, incluyendo el calibrado del modelo, experiencia previas y nuevas observaciones de campo. En los ocho eventos estudiados la conductividad media de la cuenca se obtuvo usando un procedimiento de prueba y error. Para ello se activó una opción del modelo que permite estimar para cada evento la fracción de la conductividad hidráulica saturada considerada como óptima. De este modo, mediante la interfaz de LISEM, se modificó el porcentaje Ks con respecto al valor de referencia, hasta alcanzar un ajuste visual razonable entre el caudal medido y el simulado. Tras los ajustes, el valor del parámetro E de Nash-and-Sutcliffe (1970) obtenido fue de 0,51 y el valor medio del coeficiente de correlación entre datos medidos y simulados en r2 = 0,69. El valor más bajo de Ks fue 2,48 mm/h y se obtuvo durante un evento considerado como excepcional. En los restantes siete eventos este óptimo osciló entre 3,73 y 12,01 mm/h. La conductividad hidráulica puede presentar una disminución importante en otoño. Sin embargo, las menores intensidades de infiltración a escala de cuenca tienden a ocurrir a finales de invierno y comienzos de la primavera. En base a estos resultados, se recomienda que las acciones que puedan contribuir a reducir la escorrentía y por tanto la erosión del suelo apliquen durante dicho período, dado que en él los valores de conductividad hidráulica se alejan del óptimo durante un intervalo importante / The combination of a wet climate with elevated winter precipitation, loamy-silt or loamy soils prone to crusting and rolling terrain makes the cultivated slopes of soils developed over Ordenes schist parent material in Galicia sensible to soil erosion and overland flow. To efficiently counteract erosion and runoff, it is important to know when the infiltration rate in the winter season is lowest, in the absence of soil cover. For this purpose, a deterministic, physically-based soil erosion and runoff model (LISEM) coupled to a raster GIS (PCRaster) was used. With the aid of the LISEM model, saturated hydraulic conductivity (Ks) in a small agricultural catchment was estimated by the trial-and-error method from precipitation and discharge data. Experimental data sets were measured during eight events in the 10,7 ha-sized catchment of O Abelar in the winter season of 1997/1998. Since LISEM demands a number of input data, they were retrieved from several sources, including calibration, literature and additional field observations. The catchmentaveraged saturated hydraulic conductivity was inversely modelled by trail-and-error for all eight events. For this purpose a model option to estimate the fraction of the optimal saturated hydraulic conductivity was used. The effective percentage of saturated hydraulic conductivity within the LISEM interface was adjusted until a reasonable visually fit was reached between measured and modelled discharge. The model fits had an average Nash-and- Sutcliffe (1970) E of 0,51 and an average r2 of 0,69 between measured and simulated data was obtained. The lowest value of Ks was 2,48 mm/h which was reached during an event considered to be exceptional. For seven out of eight events this figure was between 3,73 and 12,01 mm/h. The hydraulic conductivity can already drop significantly during late-autumn events. However, in general late winter-early spring is the time with the lowest infiltration rate on catchment level. Thus, management measures to mitigate runoff and erosion are recommend to be applied especially during this period, since hydraulic conductivity is least optimal for a more prolonged timeGalicia. Consellería de Economía e Industria; PGIDT01 AGR10302 PRMinisterio de Ciencia y Tecnología; REN2000-04445-C02-01-H