Academic literature on the topic 'Stepwise regression models'

Made available in DSpace on 2017-07-10T17:48:29Z (GMT). No. of bitstreams: 1 Bianchecci_Danielli_Conte.PDF: 1308564 bytes, checksum: 046371656b2367e67b20775d20072c2b (MD5) Previous issue date: 2011-12-09<br>Fundação Araucária<br>This study aimed to predict the fillet weight (PF) and fillet yield (RF) of Nile tilapia (Oreochromis niloticus) from external measures, measured by morphometry and measures of epiaxial muscles using ultrasound and validate the estimated equations using another sample biometric data. A total of 102 adult fish GIFT lineage, reversed males weighing between 260 and 580 g had the total weight (PT) and body circumference average (CR) all measured by ultrasonography in four predefined body regions (1) between the basis of anterior (2) between the basis of anteriour insertion of anal fin to the last hard ray of dorsal fin. (3) between the final insertion of anal and dorsal fins and (4) between the ventral and dorsal insertion of caudal fin. The prediction equations from the measurements performed on 50 samples were analyzed by statistical procedures backward and stepwise. The measurements made in remaining 52 samples were used for validation of predictive equations to PF and RF. The validation were made from adjustment of linear models first degree of values observed above the values predict on each regression equation set. The equations PFx and RFx estimated from data collected of ultrasound images showed coefficient of determination (R2) of 0.53 (PF1 = -17.35 + 3.66HD2 45.20LE4 + 0.55AE2 + 4.64AE4) e 0.15 (RF1 = 26.66 + 0.043AE2), in backward, and 0.53 (PF2 = -58.03 + 5.65HE4 + 0.33AD1 + 0.65AD2) e 0.19 (RF2 = 25.02 + 0.051AD2), in stepwise. The inclusion of measures of CR and PT as regressive equations did allow the equations to show higher values of R2 such as 0.97 (PF3= - 52.25 1.26HE1 2.03HE3 + 0.40PT +0.51CR e PF4 = -18.12 1.20HE1 + 0.425PT) and 0.73 (RF3 = 17.83 0.29HE1 0.49HE3 + 0.02PT + 0.13CR), in backward and stepwise, and 0.68 (RF4 = 26,14 - 0,27HE1 + 0,027PT), in stepwise, and lower values of mean square of residue that these regression models presented high adherence to data of PF and RF. About the validation of prediction equations all of it were effective in estimating the PF and RF in the sample evaluated. The equations (P = 1.0000) PF3, PF4 (P = 0.5401), RF3 (P = 1.0000) and RF4 (P = 0.8363) were the most accurate and applicable in predicting PF and RF in Nile tilapia. The height of the left side body regions 1 and 3, measured by ultrasound images, together with the average body weight and circumference, are important in predicting of regressive of PF and RF of Nile tilapia. The regression equations, PF3, PF4, RF3, and RF4 are recommended for estimating the PF and RF of Tilapia in phenotypic males adult Nile tilapia GIFT lineage, weighing between 260 and 580 g<br>Este estudo teve por objetivos predizer o peso de filé (PF) e o rendimento de filé (RF) de tilápia do Nilo (Oreochromis niloticus), a partir de medidas externas mensuradas por morfometria e medidas da musculatura epiaxial, mensuradas por ultrassonografia, e validar as equações estimadas utilizando outra amostra de dados biométricos. Um total de 102 peixes adultos, da linhagem GIFT, machos invertidos, pesando entre 260 e 580 g, foram avaliados quanto ao peso total (PT), circunferência corporal média (CR) e mensurados por ultrassonografia em quatro regiões corpóreas pré-definidas: (1) entre a base de inserção anterior da nadadeira pélvica até o término anterior da nadadeira dorsal, (2) entre a base da inserção anterior da nadadeira anal até o último raio duro da nadadeira dorsal, (3) entre a inserção final das nadadeiras anal e dorsal e (4) entre a inserção ventral e dorsal da nadadeira caudal. As equações de predição a partir das mensurações realizadas em 50 exemplares foram analisadas pelos procedimentos estatísticos backward e stepwise. As mensurações feitas nos 52 exemplares restantes foram utilizadas para a validação das equações preditoras para PF e RF. A validação foi feita a partir do ajuste de modelos lineares de 1° grau dos valores observados sobre os valores preditos por cada equação de regressão definida. As equações PFx e RFx, estimadas em função dos dados coletados das imagens ultrassonográficas, apresentaram valores de coeficiente de determinação (R²) de 0,53 (PF1 = -17,35 + 3,66HD2 - 45,20LE4 + 0,55AE2 + 4,64AE4) e 0,15 (RF1 = 26,66 + 0,043AE2), no backward, e 0,53 (PF2 = -58,03 + 5,65HE4 + 0,33AD1 + 0,65AD2) e 0,19 (RF2 = 25,02 + 0,051AD2), no stepwise. A inclusão das medidas de CR e PT como regressoras permitiu que as equações apresentassem R² mais elevados, com valores de 0,97 (PF3 = - 52,25 - 1,26HE1 - 2,03HE3 + 0,40PT +0,51CR e PF4 = -18,12 - 1,20HE1 + 0,425PT) e 0,73 (RF3 = 17,83 - 0,29HE1 - 0,49HE3 + 0,02PT + 0,13CR), no backward e no stepwise, e 0,68 (RF4 = 26,14 - 0,27HE1 + 0,027PT), no stepwise, e menores valores de quadrado médio do resíduo, indicando que esses modelos de regressão apresentaram elevada aderência aos dados de PF e RF. Na validação das equações preditoras, todas foram eficientes em estimar o PF e o RF na amostra avaliada. As equações PF3 (P = 1,0000), PF4 (P = 0,5401), RF3 (P = 1,0000) e RF4 (P = 0,8363) foram as mais precisas e aplicáveis na predição de PF e RF em tilápia do Nilo. A altura do lado esquerdo nas regiões corporais 1 e 3, mensuradas por imagens ultrassonográficas, em conjunto com o peso e a circunferência corporal média, são regressoras importantes na predição do PF e RF de tilápia do Nilo. As equações de regressão PF3, PF4, RF3 e RF4 são recomendadas para estimar o PF e o RF de tilápia no Nilo adultas, machos fenotípicos, linhagem GIFT, com peso entre 260 e 580g

O padrão espacial de ocorrência de atributos de espécies florestais, tal como a área basal das árvores, pode fornecer informações para o entendimento da estrutura da comunidade vegetal. Uma vez que fatores ambientais podem influenciar tanto o padrão espacial de ocorrência quanto os atributos das espécies em florestas nativas. Desse modo, investigar a relação entre as características ambientais e o padrão espacial de espécies florestais pode ajudar a entender a dinâmica das florestas. Especificamente, neste trabalho, o objetivo é avaliar métodos estatísticos que permitam identificar quais atributos do solo são capazes de explicar a variação da área basal de cada espécie de árvore. A área basal foi considerada como variável resposta e como covariáveis, um grande número de atributos físicos e químicos do solo, medidos em uma malha de localizações cobrindo a área de estudo. Foram revisados e utilizados os métodos de regressão linear múltipla com método de seleção stepwise, modelos aditivos generalizados e árvores de regressão. Em uma segunda fase das análises, adicionou-se um efeito espacial aos modelos, com o intuito de verificar se havia ainda padrões na variabilidade, não capturados pelos modelos. Com isso, foram considerados os modelos autoregressivo simultâneo, condicional autoregressivo e geoestatístico. Dado o grande número de atributos do solo, as análises foram também conduzidas utilizando-se as covariáveis originais, fatores identificados em uma análise fatorial prévia dos atributos de solo. A seleção de modelos com melhor ajuste foi utilizada para identificar os atributos de solo relevantes, bem como a presença e melhor descrição de padrões espaciais. A área de estudo foi a Estação Ecológica de Assis, da Unidade de Conservação do Estado de São Paulo em parcelas permanentes, dentro do projeto \"Diversidade, Dinâmica e Conservação em Florestas do Estado de São Paulo: 40 ha de parcelas permanentes\", do programa Biota da FAPESP. As análises reportadas aqui se referem à área basal das espécies Copaifera langsdorffii, Vochysia tucanorum e Xylopia aromatica. Com os atributos de solo reduzidos e consistentemente associados à área basal, a declividade, altitude, saturação por alumínio e potássio mostraram-se relevantes para duas das espécies. Resultados obtidos mostraram a presença de um padrão na variabilidade, mesmo levando-se em consideração os efeitos das covariáveis, ou seja, os atributos do solo explicam parcialmente a variabilidade da área basal, mas existe um padrão que ocorre no espaço que não é capturado por essas covariáveis.<br>The spatial pattern of occurrenceis of forest species and their attributes, such as the basal area of trees, can provide information for understanding the structure of the vegetable community. Considering the environmental factors can influence the spatial pattern of occurrences of species in native forests and related attributes, describing relationship between environmental characteristics and spatial pattern of forest species can be associated with the dynamics of forests. The objective of the present study is to assess different statistical methods used to identify which soil attributes are associated with the basal area of each tree selected species. The basal area was considered as the response variable and the covariates are given by a large number of physical and chemical attributes of the soil, measured at a grid of locations covering the study area. The methods considered are the multiple linear regression with stepwise model selection, generalized additive models and regression trees. Spatial effects were added to the models, in order to ascertain whether there is residual spatial patterns not captured by the covariates. Thus, simultaneous autoregressive model, autoregressive conditional and geostatistical were considered. Considering the large number of soil attributes, analysis were were conducted both ways, using the original covariates, and using factors identified in a preliminar factor analysis of the soil attributes. Model selection was used to identify the relevant attributes of soil as well as the presence and better description of spatial patterns. The study area was the Ecological Station of Assis, the Conservation Unit of the State of São Paulo in permanent plots within the \"Diversity Dynamics and Conservation Forests in the State of São Paulo: 40 ha of permanent plots\" project, under the research project FAPESP biota. The analyzes reported here refer to the basal area of the species Copaifera langsdorffii, Vochysia tucanorum and Xylopia aromatica. Results differ among the considered methods reinforcing the reccomendation of considering differing modeling strategies. Covariates consistently associated with basal area are slope, altitude and aluminum saturation, potassium, relevant to at least two of the species. Results obtained showed the presence of patterns in residual variability, even taking into account the effects of covariates. The soil characteristics only partially explain the variability of the basal area and there are spatial patterns not captured by these covariates.

Optimisation of the conventional tripartite of pancreatic cancer (PC) treatment have led to significant improvements in mortality, however further knowledge of the underlying molecular processes is still required. Transcript profiling of mRNA expression of over 44K genes with microarray technology demonstrated upregulation of secreted frizzled related protein 4 (sFRP4) and ??-catenin in PC compared to normal pancreata. Their pathway ??? Wnt signalling is integral to transcriptional regulation and aberrations in these molecules are critical in the development of many human malignancies. Immunohistochemistry protocols were evaluated by two independent blinded examiners for antigen expression differences associated with survival patterns in 140 patients with biopsy verified PC and a subset of 23 normal pancreata with substantial observer agreement (kappa value 0.6-0.8). A retrospective cohort was identified from 6 Sydney hospitals between 1972-2003 and archival formalin fixed tissue was collected together with clinicopathological data. Three manual stepwise regression models were fitted for overall, disease-specific and relapse-free survival to determine the value of significant prognostic variables in risk stratification. The models were fitted in a logical order using a careful strategy with step by step interpretation of the results. Immunohistochemistry demonstrated increased sFRP4 membranous expression (&gt 10%) in 49/95 PC specimens and this correlated with improved overall survival (HR:0.99;95%CI:0.97-6.40;LRchi2=134.75; 1df; ??&lt 0.001). Increased sFRP4 cytoplasmic staining (&gt 2/3) in 46/85 patients increased the disease-specific survival (HR:0.52;95%CI:0.31-0.89;LR test statistic =248.40;1df;??&lt 0.001). Increasing ??-catenin membranous expression (&lt _60%) in 26/116 patients was associated with an increased risk of overall death (HR:3.18;95%CI:1.14-8.89;LR test statistic =4.61;1df,??&lt 0.05). Increasing cytoplasmic expression in 65/114 patients was protective and was associated with prolonged survival on univariate, but not multivariate analysis (Disease specific survival HR:0.75;95%CI:0.56-1.00;logrank chi2=3.91;1df; ??=0.05). Increased nuclear ??-catenin expression in 65/114 patients was associated with prolonged survival (disease-specific HR:0.92;95%CI:0.83-1.02; LR test statistic= 49.72;1df;??&lt 0.001). At the conclusion, 12 patients (8.6%) remained alive, 122 died of their disease (68 males versus 54 females). They were followed for a median of 8.7 months (range 1.0-131.3) months. The median age was 66.5 years (range 34.4-96.0, standard deviation 10.9) years. Pancreatic resection was achieved in 79 patients with 46.8% achieving RO resection. The 30 day post-operative mortality was 2.1%. The overall 1 year survival rate was (33.7% ; 95%CI: 25.78-33.79) with a 5 year survival of (2.87%, 95%CI: 2.83-6.01) and a median survival of (8.90 months; 95%CI: 7.5-10.2). The median disease-specific survival was (9.40; 95%CI: 7.9-10.5 months) and the median time to relapse was 1.2 months (95%CI 1.0-1.2 months). A central tenet of contemporary cancer research is that an understanding of the genetic and molecular abnormalities that accompany the development and progression of cancer is critical to further advances in diagnosis, treatment and eventual prevention. High throughput tissue microarrays were used to study expression of two novel tumour markers in a cohort of pancreatic cancer patients and identified sFRP4 and ??-catenin as potential novel prognostic markers.

Construction projects in developing countries may suffer from time overruns, which are associated with cost overruns. This research project investigated both time and cost overruns on high-rise building projects in Dhaka, Bangladesh. Surprisingly, preliminary data analysis showed negligible cost overruns in comparison to time overruns. So, further analysis o f cost overruns was not considered in this thesis. This research project also investigated how the causes o f time-overruns can be mitigated. 72 time-overrun and 22 cost-overrun variables were identified through a literature review. These variables were taken as parameters and a personal interview survey was conducted with developers, consultants, contractors and project managers using semistructured questionnaire. A similar second survey was conducted using 22 measures, which can mitigate time- overruns. Data analysis involved the relative importance index to rank the variables, factors analysis to reduce variables to factors with minimum loss of data, stepwise regression to find links among factors in successive stages of construction process and multiple regression to explain delays in terms of factors. The main causes o f time-overruns were ‘cash flow’, ‘planning and scheduling deficiency’ and ‘design changes’. A scree graph identified 31 important variables that caused delays but factor analysis reduced these to 14 factors. Stepwise regression found no strong links among the factors to identify them as reasons for delay in successive stages of the construction project. A multiple regression model explained about 85% of the variance of the delays using eight factors. The main individual measures mitigating time-overruns were ‘improvement of cash flow’, ‘improvement o f communication and coordination among project participants’ and ‘development o f robust planning and scheduling instruments’. Factor analysis produced ten representative factors. Stepwise regression could not find strong links among factors mitigating time-overruns in successive stages of the construction project.

Doctor of Philosophy<br>Department of Human Nutrition<br>Edgar Chambers IV<br>Companies introduce new products with the goal of achieving success. However, many products fail. The overall objective of this research was to design processes for determining sensory and market characteristics of food products that could predict success. The first sub-objective was to determine if success could be predicted using information known before launch. The second sub-objective was to describe a process for determining specific sensory characteristics that promote success. Most methods chosen for this research are commonly used. However, previous research has identified a relationship between consumers liking and salivation, without defining a method. Thus, three salivation methods were selected for initial testing: spit, cotton rolls and sensory scale. These were tested on foods with different textures. Although all methods gave similar results, the spit method was chosen for further testing of flavor differences. Differences in salivation measurements were found for snacks where flavors were different but texture was unchanged. Next, flavored snack products from 15 countries were selected that were successful or had failed. Questionnaires were completed for each product and included questions related to authenticity, familiarity, current trends, packaging and marketplace issues such as product competition and pricing, all of which would be known before launch. A discriminant function was developed that correctly identified 75.8% of the successful flavored snack products as successful and 66.7% of the unsuccessful products as unsuccessful. Stepwise comparisons were used to determine that four variables are necessary to correctly categorize these products. The products then were clustered into three groups to select 34 products from 11 countries for further sensory testing. Information from extensive sensory descriptive methods were evaluated individually and in various combinations through stepwise regression and discriminant analysis. The final sensory model correctly predicted all successful and unsuccessful products, had an R-square of 0.84 and included nine regression factors: seven flavor attributes and two flavor attribute ratios. Many of the attributes were base flavor notes necessary for this flavored snack category. A process for selecting key attributes for success was described. For this snack category, creating products with flavors that interact well with base flavor notes can lead to a successful product.

The dissertation focuses on the different determinants of education, their effects on the educational outcome, and the overall effect of education on the lifetime consequences. The first chapter focuses on the inequality of educational opportunity across different demographic factors. This chapter employs a broader set of social factors to provide fresh insights into the inequality situation in the USA relative to those of the extant literature. The chapter employs polynomial trends for the effects of social factors to identify long-term trends in the determinants of the differences in attainment of each of four achievements (high school graduation, some college, college graduation, and post-college work) across different endogenous social groups. Using the Panel Study of Income Dynamics (PSID) data for the years of 1968-2013, we show how inequality of educational opportunity and its determinants have evolved over the years. The chapter utilizes the machine-learning process and logistic regression model to identify inequality of opportunity. The second chapter examines the age demographic distribution of graduates across cohorts from 1940 until 1990. Using the PSID data, the paper explored the first and second moment of the age of graduating from high school and college across the US. To deal with the data deficiencies, a large part of the chapter dealt with data preparation. The chapter provides a unique method of extracting information on the graduating age of the individuals both from high school and from college. The results show a large dispersion across the full sample. The data truncated to a standard length, however, provides a much smaller dispersion and much smaller moments. The chapter concludes that as the time passes, people tend to attain education at a younger age. The third chapter investigates the trends of the contribution of different factors of income starting from 1910 cohort. Following Mincer (1974), a wave of papers studied how various factors contribute to the earnings of individuals. This paper contributes to that literature in three ways: (i) using the PSID data, it computes the actual working experience of the individuals, (ii) it studies the cohorts who were born in 1910 or afterwards, unlike the existing papers, and (iii) it adds two variables�"technological progress and the occupation with which individuals start their careers�"to an extended Mincerian equation. The results re-emphasize the importance of education in lifetime earnings. The results also show that while some of the determinants of income have become more important over the years, other factors have not changed much in importance.<br>PHD

This doctoral study aims to develop a methodology for use in determining aerodynamic models and parameters from actual flight test data for different types of autonomous flight vehicles. The stepwise regression method and equation error method are utilized for the aerodynamic model identification and parameter estimation. A closed loop aerodynamic parameter estimation approach is also applied in this study which can be used to fine tune the model parameters. Genetic algorithm is used as the optimization kernel for this purpose. In the optimization scheme, an input error cost function is used together with a final position penalty as opposed to widely utilized output error cost function. Available methods in the literature are developed for and mostly applied to the aerodynamic system identification problem of piloted aircraft<br>a very limited number of studies on autonomous vehicles are available in the open literature. This doctoral study shows the applicability of the existing methods to aerodynamic model identification and parameter estimation problem of autonomous vehicles. Also practical considerations for the application of model structure determination methods to autonomous vehicles are not well defined in the literature and this study serves as a guide to these considerations.