8 resultados para Regression logistic

em Instituto Politécnico do Porto, Portugal


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Dissertação para obtenção do Grau de Mestre em Contabilidade e Finanças Orientador: Doutor José Manuel da Veiga Pereira

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Long-term contractual decisions are the basis of an efficient risk management. However those types of decisions have to be supported with a robust price forecast methodology. This paper reports a different approach for long-term price forecast which tries to give answers to that need. Making use of regression models, the proposed methodology has as main objective to find the maximum and a minimum Market Clearing Price (MCP) for a specific programming period, and with a desired confidence level α. Due to the problem complexity, the meta-heuristic Particle Swarm Optimization (PSO) was used to find the best regression parameters and the results compared with the obtained by using a Genetic Algorithm (GA). To validate these models, results from realistic data are presented and discussed in detail.

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Background: Diet and physical activity (PA) are recognized as important factors to prevent abdominal obesity (AO), which is strongly associated with chronic diseases. Some studies have reported an inverse association between milk consumption and AO. Objective: This study examined the association between milk intake, PA and AO in adolescents. Methods: A cross-sectional study was conducted with 1209 adolescents, aged 15–18 from the Azorean Archipelago, Portugal in 2008. AO was defined by a waist circumference at or above the 90th percentile. Adolescent food intake was measured using a semi-quantitative food frequency questionnaire, and milk intake was categorized as ‘low milk intake’ (<2 servings per day) or ‘high milk intake’ ( 2 servings per day). PA was assessed via a self-report questionnaire, and participants were divided into active (>10 points) and low-active groups ( 10 points) on the basis of their reported PA. They were then divided into four smaller groups, according to milk intake and PA: (i) low milk intake/low active; (ii) low milk intake/active; (iii) high milk intake/low active and (iv) high milk intake/active. The association between milk intake, PA and AO was evaluated using logistic regression analysis, and the results were adjusted for demographic, body mass index, pubertal stage and dietary confounders. Results: In this study, the majority of adolescents consumed semi-skimmed or skimmed milk (92.3%). The group of adolescents with high level of milk intake and active had a lower proportion of AO than did other groups (low milk intake/low active: 34.2%; low milk intake/active: 26.9%; high milk intake/low active: 25.7%; high milk intake/active: 21.9%, P = 0.008). After adjusting for confounders, low-active and active adolescents with high levels of milk intake were less likely to have AO, compared with low-active adolescents with low milk intake (high milk intake/low active, odds ratio [OR] = 0.412, 95% confidence intervals [CI]: 0.201– 0.845; high milk intake/active adolescents, OR = 0.445, 95% CI: 0.235–0.845).Conclusion: High milk intake seems to have a protective effect on AO, regardless of PA level

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Background and aim: Cardiorespiratory fitness (CRF) and diet have been involved as significant factors towards the prevention of cardio-metabolic diseases. This study aimed to assess the impact of the combined associations of CRF and adherence to the Southern European Atlantic Diet (SEADiet) on the clustering of metabolic risk factors in adolescents. Methods and Results: A cross-sectional school-based study was conducted on 468 adolescents aged 15-18, from the Azorean Islands, Portugal. We measured fasting glucose, insulin, total cholesterol (TC), HDL-cholesterol, triglycerides, systolic blood pressure, waits circumference and height. HOMA, TC/HDL-C ratio and waist-to-height ratio were calculated. For each of these variables, a Z-score was computed by age and sex. A metabolic risk score (MRS) was constructed by summing the Z scores of all individual risk factors. High risk was considered when the individual had 1SD of this score. CRF was measured with the 20 m-Shuttle-Run- Test. Adherence to SEADiet was assessed with a semi-quantitative food frequency questionnaire. Logistic regression showed that, after adjusting for potential confounders, unfit adolescents with low adherence to SEADiet had the highest odds of having MRS (OR Z 9.4; 95%CI:2.6e33.3) followed by the unfit ones with high adherence to the SEADiet (OR Z 6.6; 95% CI: 1.9e22.5) when compared to those who were fit and had higher adherence to SEADiet.

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A afluência desmedida aos Serviços de Urgência é uma questão que acarreta preocupações a nível financeiro. Contribui para este fato, a mentalidade da população, que acredita que este serviço oferece mais facilidades de acesso, dispõe de mais recursos e fornece melhores cuidados de saúde. Novas medidas foram preconizadas, como o aumento das taxas moderadoras, para tentar travar este fenómeno. No entanto, apesar da descida dos episódios de urgência em cerca de 10%, em Portugal, estudos apontam para valores na ordem dos 30-35% de episódios não urgentes. Assim, torna-se importante que não só se enfatizem as novas medidas, como se eduque a população com vista à correta utilização destes serviços, através de campanhas de sensibilização. Torna-se, assim, necessário que se chegue ao perfil do utilizador abusivo. Para a identificação de um perfil de abusividade, foram solicitados dados de episódios de urgência ocorridos durante um período de 6 meses no Hospital de São João, tendo depois sido estimado um modelo de regressão logística. A metodologia permite identificar quais as características que influenciam uma utilização abusiva do serviço e quantificar o impacto de cada uma destas características na probabilidade de um utente apresentar um comportamento abusivo. Concluiu-se que, uma mulher entre os 18-30 anos, que resida em Vila Nova de Gaia, recorra à urgência durante a noite tendo-lhe sido atribuída uma pulseira azul e seja abrangida pelo Serviço Nacional de Saúde, apresenta 91,92% de probabilidade de utilizar este serviço de forma abusiva. Contrariamente, um homem com mais de 60 anos, residente na Maia, que recorra ao serviço durante o dia, esteja isento do pagamento de taxas moderadoras e seja abrangido pela ADSE, e lhe seja atribuída uma pulseira laranja, apresenta apenas 39,93% de probabilidade de ter um comportamento abusivo. Estes resultados são importantes para definir campanhas de sensibilização que diminuam comportamentos abusivos.

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The prediction of the time and the efficiency of the remediation of contaminated soils using soil vapor extraction remain a difficult challenge to the scientific community and consultants. This work reports the development of multiple linear regression and artificial neural network models to predict the remediation time and efficiency of soil vapor extractions performed in soils contaminated separately with benzene, toluene, ethylbenzene, xylene, trichloroethylene, and perchloroethylene. The results demonstrated that the artificial neural network approach presents better performances when compared with multiple linear regression models. The artificial neural network model allowed an accurate prediction of remediation time and efficiency based on only soil and pollutants characteristics, and consequently allowing a simple and quick previous evaluation of the process viability.

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Women account for 30% of all AIDS cases reported to the Health Ministry in Portugal and most infections are acquired through unprotected heterosexual sex with infected partners. This study analyzed socio-demographic and psychosocial predictors of consistent condom use and the role of education as a moderator variable among Portuguese women attending family planning clinics. A cross-sectional study using interviewer-administered fully structured questionnaires was conducted among 767 sexually active women (ages 18–65). Logistic regression analyses were used to explore the association between consistent condom use and the predictor variables. Overall, 78.7% of the women were inconsistent condom users. The results showed that consistent condom use was predicted by marital status (being not married), having greater perceptions of condom negotiation self-efficacy, having preparatory safer sexual behaviors, and not using condoms only when practicing abstinence. Living with a partner and having lack of risk perception significantly predicted inconsistent condom use. Less educated women were less likely to use condoms even when they perceive being at risk. The full model explained 53% of the variance in consistent condom use. This study emphasizes the need for implementing effective prevention interventions in this population showing the importance of taking education into consideration.

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Este estudo pretende (1) encontrar a prevalência da Perturbação do Desenvolvimento da Coordenação (PDC) em crianças com Perturbação de Hiperatividades e Défice de Atenção (PHDA); (2) analisar qual a prevalência de défices de memória de trabalho verbal e não-verbal, em crianças com PHDA e comparar o desempenho entre as crianças que só apresentam PHDA e aquelas que apresentam também PDC; (3) verificar se a ocorrência de PDC é agravada, de acordo com a presença ou ausência de alterações de memória de trabalho e se estas podem ser consideradas fatores de risco ou de proteção para a manifestação de PDC, enquanto comorbilidade de PHDA. Foram selecionadas 37 crianças com diagnóstico de PHDA, com idades compreendidas entre os 7 e os 14 anos. A componente motora foi avaliado com a versão curta do Bruininks-Oseretsky Test of Motor Proficiency (BOTMP) e o Questionário de Perturbação do Desenvolvimento da Coordenação 2007 (DCDQ’07); a memória de trabalho foi avaliada através da Figura Complexa de Rey, Trail Making Test - parte B e Memória de Dígitos – sentido inverso. Para determinar o impacto da memória de trabalho na componente motora, recorreu-se a uma regressão logística. Encontrou-se uma prevalência de PDC de 51% e de défices ao nível da memória de trabalho verbal e não-verbal de 60% e 80%, respetivamente, para a amostra total de crianças com PHDA. A terapêutica farmacológica para a PHDA revelou-se fator protetor para a manifestação de PDC, principalmente quando a primeira se encontra associada com o nascimento de termo. Um mau desempenho no teste Memória de Dígitos – sentido inverso é fator de risco para a manifestação de PDC, em crianças com PHDA. Este estudo permitiu verificar que crianças com PHDA+PDC apresentam défices motores genuínos, característicos de manifestação de PDC. Parecem também existir relações bastante complexas entre a memória de trabalho e os mecanismos de controlo motor na PHDA, sendo que estes podem ser distintos quando está presente uma comorbilidade de PDC.