Suchergebnisse

"Structural Equation Modelling (SEM) is a relatively recently developed statistical technique based upon factor analysis and multiple regression. This review will cover four of the most widely used (in psychology departments) packages, looking in particular at their suitability for use in a teaching environment, rather than an in depth look at their technical capabilities: LISREL 8.20, EQS 5.6, AMOS 3.6, SEPath. The four programs reviewed were all tested running Windows 95, on a 166 MHz Pentium, with 32 MB RAM." (author's abstract)

Tesis para obtener el grado de Doctor of Philosophy (PhD), de la Wageningen University, en marzo de 2018 ; Climate change and land degradation are of increasing societal and governmental concern. For this reason, several international programs have been initiated in the last decade, such as the 4 per 1000 initiative and the Sustainable Development Goals of United Nations. The soil science community is actively working under different national and international organizations to provide regional and global soil information to support these programmes. Digital Soil Mapping (DSM), a relatively new methodology to create soil maps based on (geo)statistical methods, has became operational during the last fifteen years and has now been adopted by several organizations. It is defined as computer-assisted production of digital maps of soil type and soil properties, by use of mathematical and statistical models that combine information from soil observations with information contained in correlated environmental variables. Most studies in DSM spatially predict soil properties or classes from either new or legacy laboratory data and spatially exhaustive environmental covariates (GIS layers of biophysical land surface properties), typically using empirical statistical methods. These methods have shown to result in accurate maps at different scales, but do not provide knowledge about the interrelationships between the soil properties and the functioning of the soil and soil-landscape system. We not only need to properly describe or map soil spatial variation, but also to understand soil behaviour. This is needed to answer questions such as: which are the dominant soil processes in a certain region? How will the soil react under increased productivity pressure? How vulnerable is the soil to erosion or pollution? How much organic carbon can we store in the soil at a given location? Mechanistic soil-landscape models do include process-knowledge but cannot be applied easily for soil mapping because of their high complexity and large uncertainty. A solution could be to use structural equation modelling (SEM), which is a hybrid approach that combines elements of empirical and mechanistic models. SEM can model continuous soil properties while taking soil property interrelationships into account. In SEM, we first create a conceptual model, similar to the mental model of soil surveyors, which is converted into a graphical model, that represents the system interrelationships. This is the mechanistic side of SEM. The empirical side takes place after we translated the graphical model into a mathematical model, which is calibrated with observational data to estimate the model coefficients. Next, the calibrated model can be used to predict target variables, such as soil properties. These characteristics of SEM indicate that it could be a very useful technique to bridge the gap between empirical and mechanistic approaches for DSM. Thus, the objective of this thesis is to extend DSM with soil process information through the development, calibration, application and validation of a structural equation model. ; El cambio climático y la degradación del suelo son problemas cada vez más preocupantes para la sociedad y los gobiernos. Por este motivo se han iniciado numerosos programas internacionales en la última década, como por ejemplo la iniciativa 4 per 1000 y los Objetivos de Desarrollo Sustentable de las Naciones Unidas. La comunidad científica del suelo está trabajando activamente bajo diferentes organizaciones nacionales e internacionales para proporcionar información de este recurso a escala regional y mundial. Para ello, durante los últimos quince años se ha implementado el Mapeo Digital de Suelos (DSM, por sus siglas en Inglés Digital Soil Mapping), una metodología relativamente nueva para crear mapas de suelos, y que ahora está siendo adoptada por varias organizaciones, entre ellas la FAO. El DSM se define como la producción asistida por computadora de mapas digitales de tipos y propiedades de suelo, mediante el uso de modelos matemáticos y estadísticos que combinan información de observaciones del suelo con información contenida en variables ambientales correlacionadas. La mayoría de los estudios que emplean DSM predicen las propiedades o clases de suelos espacialmente a partir de datos de laboratorio (nuevos o legados de previos relevamientos) y de covariables ambientales (capas GIS de propiedades biofísicas de la superficie terrestre). Generalmente se utilizan métodos estadísticos empíricos, que han demostrado producir mapas precisos a diferentes escalas. Sin embargo, estos métodos no generan conocimientos sobre las relaciones entre propiedades del suelo y sobre la relación suelo-paisaje. Los mapas de suelos no sólo necesitan describir apropiadamente la variación espacial del mismo, sino también proveer información de su comportamiento. Este tipo de información es necesaria para responder a preguntas tales como: ¿cuáles son los procesos dominantes del suelo en una determinada región? ¿Cómo reaccionará el suelo bajo una mayor presión de productividad? ¿Qué tan vulnerable es el suelo a la erosión o la contaminación? ¿Cuánto carbono orgánico podemos almacenar en el suelo en un lugar determinado? Otros modelos utilizados en el estudio de las variaciones espaciales de los suelos son los modelos mecanísticos (también llamados modelos físicos) que incluyen procesos físico-químicos que ocurren en el sistema suelo-paisaje. Sin embargo, no se pueden aplicar fácilmente al mapeo de suelos debido a su alta complejidad y gran incertidumbre. Una solución intermedia entre los modelos empíricos y los modelos mecanísticos sería utilizar modelos de ecuaciones estructurales (SEM, por sus siglas en Inglés Structural Equation Modelling). Mediante SEM se puede modelar propiedades continuas del suelo teniendo en cuenta las interrelaciones existentes entre ellas. En SEM, primero se crea un modelo conceptual, similar al modelo mental que desarrollaban los clásicos reconocedores de suelos. Este modelo conceptual es posteriormente transformado en un modelo gráfico, el cual representa las interrelaciones del sistema. Luego, el modelo gráfico se traduce a un modelo matemático que se calibra con datos medidos de las propiedades involucradas dando como resultado los coeficientes del modelo. A continuación, el modelo calibrado se puede utilizar para predecir las propiedades de suelo. Estas características de SEM lo convierten en una herramienta útil para cerrar la brecha entre los enfoques empíricos y mecánisticos en DSM. Por lo tanto, el objetivo de esta tesis es expandir las metodologías de DSM mediante la incorporación de conocimiento pedológico a través del desarrollo, calibración, aplicación y validación de un modelo de ecuaciones estructurales. ; Instituto de Suelos ; Fil: Angelini, Marcos Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Suelos; Argentina.

Agriculture sector is seen as a low-tech and unorganised industry with limited changing aspects dominated by number of small family firms mostly focused on doing traditional things better rather than doing things with modern approach. This situation has changed intensely due to globalisation, economic liberalization, and reduced protection of agricultural markets in last few decades. Recently global agricultural industries have to change their operations as per the changing markets, environmental regulations, consumer habits, product quality, chain management, sustainability, food safety, and so on. These changes,innovation, and opportunities in agro sectors are initiating the scope for various entrepreneurship opportunities. Since long, it is recognized by various government authorities, politicians, agricultural industry practitioners as well as scientists that farmers intensively require agricultural entrepreneurship along with traditional agricultural business for sustainable future. The purpose of this study is to understand the motivation for agricultural entrepreneurship among management students. This study will investigate whether different motivational factors exists based on types of fields, farms, crops and agricultural operations. This study analyses student's intension towards the existing rural entrepreneurship and attempt to study the problems and challenges in its growth. The major objectives of this research include the focus on identifying student's interest, scope, opportunities and challenges in agricultural entrepreneurship to contribute to the rural economy.The scope of this study is related to the rural economy and business opportunities that exist in a rural area.

Mestrado em Desenvolvimento e Cooperação Internacional ; Este trabalho visa analisar o contexto de economia rural em três distritos da região Sul de Mozambique, para demonstrar a existência de mecanismos "aprisionadores" que detêm as famílias camponesas numa condição de pobreza. Todas as variáveis tomadas em conta para o estudo resultam de uma base de dados autoproduzida que inclui informação sobre a subsistência no contexto rural e o sector agrícola. Este trabalho utiliza a abordagem dos modelos de equações estruturais (SEM) para detectar as possíveis não-linearidades no processo de criação de riqueza, em particular a través da análise da saúde, do contexto institucional e de mercado, e da segurança alimentar em relação à riqueza das famílias. Recorrendo aos conceitos de complexidade, multidimensionalidade e causação cumulativa, procura-se demonstrar a existência de uma "armadilha da pobreza" a partir da análise das diversas dinâmicas relacionadas com a relação que existe entre segurança alimentar e bem-estar das famílias inquiridas. A metodologia adotada neste trabalho constitui uma alternativa aos testes tradicionalmente utilizados na investigação sobre as armadilhas da pobreza, pois inclui um numero maior de factores na analise da pobreza persistente. Em conclusão, os resultados da estimação do modelo fornecem algumas recomendações em termos de politicas de combate contra a pobreza, de acordo com as características especificas da zona. ; This article analyses the rural economy of three districts in southern Mozambique, proving the existence of a lock-in device that keeps small-scale farmers and their households into poverty. All variables taken into account result from an original survey-based dataset which includes socio-economic information about rural livelihoods and the agricultural sector. A Structural Equation Modelling approach is adopted to detect non-linearity in wealth creation - in particular by analysing health, market/institutional environment and food security in relation to an asset-based measure of wealth. Drawing upon the concepts of complexity, multidimensionality and cumulative causation, this work proves the existence of a poverty trap by analysing the varying dynamics related to the relationship that exists between food security and wealth. The methodology adopted in this work represents an alternative to the traditional tests usually applied for the detection of poverty traps, including a wider number of factors in the study of persistent poverty; finally, it provides some useful policy recommendations regarding the struggle against poverty in this area. ; N/A

This study investigated the users' assessment of affordable housing in developing cities among the residents of Ibadan urban centre. Affordable housing entails users having access to quality housing at reasonable prices, obtaining it, maintaining the ability to meet other basic costs of living and to stay in it without any problem in order to promote good health, accessibility, convenience and environment that is free from crime and violence. The study developed a theoretical model that links users' assessment to the affordable housing. Questionnaire was developed and administered to 494 residents in the five local government areas within Ibadan. The data was analysed using statistical packages SPSS and AMOS version 22. Exploratory factor analysis and confirmatory factor analysis techniques were applied to evaluate the users' assessment of affordable housing. The structural equation modelling as the validated measuring tools was employed to validate the theoretical model. The finding indicated that detailed examination, assessment and critical reflection of users on their affordable housing is an important step towards designing policies to improve affordable housing that is accessible to users. The authors are of the opinion that strategies through the employment of suitable housing policy are needed to address the challenge of existing affordable housing in developing cities.