http://hdl.handle.net/10362/2281 Sat, 18 May 2013 04:25:35 GMT 2013-05-18T04:25:35Z http://hdl.handle.net/10362/8858 Title: Modelling HIV/AIDS length of stay in Portugal Authors: Dias, Sara Alexandra da Fonseca Marques Simões Abstract: The introduction of highly active antiretroviral therapy (HAART) in late 1996 dramatically improved the prognosis of Human Immunodeficiency Virus (HIV) infected patients in most developed countries and also the number of newly infected adults and children. Despite declining mortality over the last years, adult HIV prevalence in 2007 ranges from 0.1% to 0.6% in Europe. Portugal is one of the European countries with the highest prevalence (0.5%), where 31,667 cases of HIV/AIDS were notified in 2007. HIV/AIDS was chosen as the focus of this Thesis, because the hospitalizations are one of the major financial burdens on healthcare systems worldwide. In Portugal, hospitalizations related to HIV infection are also some of the most expensive; in 2006, the average daily cost was around €825 and it was the second major diagnosis category (MDC) with the greatest average hospitalization time. In the same year, the average length of stay (LOS) in Portuguese hospitals of the National Health Service (NHS) was 23 days. With this Thesis I intend to contribute to a better understanding of the factors associated with HIV/AIDS LOS, taking into consideration that LOS data are usually right skewed and heterogeneous, representing a challenge for modelling and statistical analysis. The literature review reveals the need to analyse HIV/AIDS LOS through two different statistical points of view: survival analysis and mixture models. This Thesis is organised as follows: in the first chapter is an introduction, the literature review is presented in the second chapter, the third chapter presents the statistical methodologies developed during the Thesis, in the following three chapters I present the different studies regarding HIV/AIDS LOS and the last chapter presents a general conclusion. In three studies I analyse the Portuguese national database of all patient refined diagnosis related groups (DRG) that were provided by the Central Administration of Health Systems (ACSS). The data are anonymous and available for scientific research. In the DRG database each record corresponds to a discharge episode (hospitalization) and contains information collected while the patient was hospitalized. In the first study the population consists of 12,078 adult discharges of patients with HIV infection treated at Portuguese hospitals from 2005‐2007 that were registered on the DRG’s database. Discharge and hospital level variables were used to develop a hierarchical model. Kaplan‐Meier plots were used to examine differences in survival curves. Cox proportional hazard model and Cox proportional hazard model with frailty were applied to identify independent predictors of hospital mortality and to calculate hazard ratios (HR). The frailty model suggests that there are unmeasured factors affecting mortality in HIV associated hospitalizations. In the second study a hierarchical finite mixture model was developed to identify factors that are associated with HIV/AIDS. A mixture of normal components is applied to adult HIV/AIDS diagnosis‐related group data from 2008. The model accounts for demographic and clinical characteristics of the patients, as well as the inherent correlation of patients clustered within hospitals. A normal mixture distribution was fitted to the logarithm of LOS and it was found that the model with two‐components had the best fit, resulting in two subgroups of LOS: a short‐stay subgroup and a long‐stay subgroup. Associated risk factors for both groups were identified as well as some statistical differences in the hospitals. The third study presents a finite mixture Poisson regression model to analyse HIV/AIDS LOS. The statistical methodology proposed allows that different covariates explain different components (nested varying parameters), and those factors found to be significant may be compared and contrasted between subgroups. The model with three components was the one with the best fit, resulting in three subgroups of LOS: a short‐stay, a medium‐stay and a longstay subgroup. It was also found that gender and number of procedures are the only variables important to explain the three groups. With this Thesis I conclude that it is very important to have comprehensive and accurate information about LOS in order to develop strategic planning and to deploy financial, human, and physical resources of the hospitals. In addition, the determination of patient related characteristics affecting LOS can help physicians optimize care and rationalize their medical practice. Description: Tese apresentada como requisito parcial para obtenção do grau de Doutor em Estatística e Gestão de Informação pelo Instituto Superior de Estatística e Gestão de Informação da Universidade Nova de Lisboa Tue, 26 Jun 2012 00:00:00 GMT http://hdl.handle.net/10362/8858 2012-06-26T00:00:00Z http://hdl.handle.net/10362/8631 Title: From the portolan chart of the mediterranean to the latitude chart of the atlantic Authors: Gaspar, Joaquim Filipe Figueiredo Alves Abstract: In this thesis a methodology for the systematic geometric analysis and modeling of pre-Mercator nautical charts is proposed and tested, aiming at contributing to better understand their geometric properties and methods of construction. The suggested approach involves the application of a series of cartometric techniques: georeferencing, on the basis of a sample of control points of known geographic coordinates; the interpolation of the geographical graticules implicit to the representations; the assessment of scales of distance and latitude; the assessment of the navigational accuracy, by comparing the latitudes, directions and distances measured on the charts with the corresponding exact values, affected by magnetic declination; and the identification of the routes underlying the charts’ construction. A numerical model was developed using the concept of ‘multimensional scaling’, here generalized to distances and directions measured on a spherical Earth, to simulate the main geometric features of the charts. To estimate the spatial distribution of the magnetic declination in various times two sources were used: the historical observations made by D. João de Castro in 1538 and 1541, and a recent geomagnetic model. Description: Thesis submitted to the Instituto Superior de Estatística e Gestão de Informação da Universidade Nova de Lisboa in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Information Management – Geographic Information Systems Tue, 21 Sep 2010 00:00:00 GMT http://hdl.handle.net/10362/8631 2010-09-21T00:00:00Z http://hdl.handle.net/10362/8217 Title: Regional change in the Algarve: A Geographic Information System approach Authors: Vaz, Erich Moreira de Noronha Abstract: The debate on sustainable development has led to an increasing interest covering the effects of the human beings on the natural environment. The development of information and communication technologies (ICT) allowed a better analysis of the drivers of environmental change. With the increase of ICT, especially related to monitoring of sustainable choices, methodologies for analysis of regional and local impact have made a significant contribution to the development of regional strategies at a policy level, but also contributed to the development of regional sciences. One of the main issues has been addressed by the analysis of carrying capacity and availability of scarce resources, resulting from a growing demand, leading to loss of vulnerable natural and historical areas. Much of the work of regional sciences has had a direct relation to space, due to the nature of socio-economic data. This thesis offers an integrated spatial assessment of the results of regional change brought by socio-economic growth. The Algarve region in Portugal is used as a laboratory to understand the current pressures and attempts to provide a framework for the future of socio-economic growth in the region and a systematic analysis of current pressures. While urban sprawl due to increasing tourist activity is an increasing concern, spatial analysis is used as an insightful tool for foresight of future change. Having considered that urban growth is a direct consequence of economic growth our research addresses the consequences of urban sprawl in the coastal region of the Algarve. By building up predictive tools for complex spatial system analysis, cellular automata are used to forecast future urban expansion in the region. The relationship of tourism to urban change is measured to assess what are true costs of tourism for the region. Tourism is then analysed within the duality of socio-economic pressures defining weak and strong sustainability. An integrated strategy considering the historical heritage of the Algarve is offered as a more interesting alternative to the current exploration of the marine environment. Thus, the dissertation expands on the usage of spatial analysis as tools to emphasize the importance of monitoring regional change in coastal environments from a socio-economic perspective. Geographic Information Systems are expressed as ubiquitous systems with unique properties to measure change and to offer relevant solutions for better decision making at local and regional level. An important asset of those tools in the context of information management is further explored in the capabilities of comparing results through spatial data manipulation and visualization of alternative futures for regional development. Description: Thesis submitted to the Instituto Superior de Estatística e Gestão de Informação da Universidade Nova de Lisboa in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Information Management – Geographic Information Systems Mon, 26 Sep 2011 00:00:00 GMT http://hdl.handle.net/10362/8217 2011-09-26T00:00:00Z http://hdl.handle.net/10362/6735 Title: Estimation Models for the adoption and use of information technology: internet-related technologies at firm level in the Portuguese and European context Authors: Oliveira, Tiago André Gonçalves Félix de Abstract: Nowadays it is consensual that information technology (IT) has a significant effect in the productivity of firms. However, this contribution can only be accomplishe if, and when, the new IT are widely spread and used. Understanding the determinants of adoption and use is a fundamental question, not only for economists, but also for society in general.(...) Description: Dissertação apresentada como requisito parcial para obtenção do grau de Doutor em Gestão de Informação Thu, 13 Jan 2011 00:00:00 GMT http://hdl.handle.net/10362/6735 2011-01-13T00:00:00Z