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Simon N. Wood - One of the best experts on this subject based on the ideXlab platform.
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on p values for smooth components of an extended Generalized Additive Model
Biometrika, 2013Co-Authors: Simon N. WoodAbstract:The problem of testing smooth components of an extended Generalized Additive Model for equality to zero is considered. Confidence intervals for such components exhibit good across-the-function coverage probabilities if based on the approximate result \hat f(i) ~ N{f(i),V_f(i,i)}, where f is the vector of evaluated values for the smooth component of interest and V_f is the covariance matrix for f according to the Bayesian view of the smoothing process. Based on this result, a Wald-type test of f=0 is proposed. It is shown that care must be taken in selecting the rank used in the test statistic. The method complements previous work by extending applicability beyond the Gaussian case, while considering tests of zero effect rather than testing the parametric hypothesis given by the null space of the component’s smoothing penalty. The proposed p-values are routine and efficient to compute from a fitted Model, without requiring extra Model fits or null distribution simulation.
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coverage properties of confidence intervals for Generalized Additive Model components
Scandinavian Journal of Statistics, 2012Co-Authors: Giampiero Marra, Simon N. WoodAbstract:We study the coverage properties of Bayesian confidence intervals for the smooth component functions of Generalized Additive Models (GAMs) represented using any penalized regression spline approach. The intervals are the usual generalization of the intervals first proposed by Wahba and Silverman in 1983 and 1985, respectively, to the GAM component context. We present simulation evidence showing these intervals have close to nominal ‘across-the-function’ frequentist coverage probabilities, except when the truth is close to a straight line/plane function. We extend the argument introduced by Nychka in 1988 for univariate smoothing splines to explain these results. The theoretical argument suggests that close to nominal coverage probabilities can be achieved, provided that heavy oversmoothing is avoided, so that the bias is not too large a proportion of the sampling variability. Otherwise, because the Bayesian intervals account for bias and variance, the coverage probabilities are surprisingly insensitive to the exact choice of smoothing parameter. The theoretical results allow us to derive alternative intervals from a purely frequentist point of view, and to explain the impact that the neglect of smoothing parameter variability has on confidence interval performance. They also suggest switching the target of inference for component-wise intervals away from smooth components in the space of the GAM identifiability constraints. Instead intervals should be produced for each function as if only the other Model terms were subject to identifiability constraints. If this is done then coverage probabilities are improved.
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fast stable direct fitting and smoothness selection for Generalized Additive Models
Journal of The Royal Statistical Society Series B-statistical Methodology, 2008Co-Authors: Simon N. WoodAbstract:Existing computationally efficient methods for penalized likelihood Generalized Additive Model fitting employ iterative smoothness selection on working linear Models (or working mixed Models). Such schemes fail to converge for a non-negligible proportion of Models, with failure being particularly frequent in the presence of concurvity. If smoothness selection is performed by optimizing 'whole Model' criteria these problems disappear, but until now attempts to do this have employed finite-difference-based optimization schemes which are computationally inefficient and can suffer from false convergence. The paper develops the first computationally efficient method for direct Generalized Additive Model smoothness selection. It is highly stable, but by careful structuring achieves a computational efficiency that leads, in simulations, to lower mean computation times than the schemes that are based on working Model smoothness selection. The method also offers a reliable way of fitting Generalized Additive mixed Models. Copyright (c) 2008 Royal Statistical Society.
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Fast stable direct fitting and smoothness selection for Generalized Additive Models
Journal of the Royal Statistical Society: Series B (Statistical Methodology), 2008Co-Authors: Simon N. WoodAbstract:Existing computationally efficient methods for penalized likelihood Generalized Additive Model fitting employ iterative smoothness selection on working linear Models (or working mixed Models). Such schemes fail to converge for a non-negligible proportion of Models, with failure being particularly frequent in the presence of concurvity. If smoothness selection is performed by optimizing ‘whole Model’ criteria these problems disappear, but until now attempts to do this have employed finite-difference-based optimization schemes which are computationally inefficient and can suffer from false convergence. The paper develops the first computationally efficient method for direct Generalized Additive Model smoothness selection. It is highly stable, but by careful structuring achieves a computational efficiency that leads, in simulations, to lower mean computation times than the schemes that are based on working Model smoothness selection. The method also offers a reliable way of fitting Generalized Additive mixed Models
Bruno Spire - One of the best experts on this subject based on the ideXlab platform.
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a Generalized Additive Model to disentangle age and diagnosis specific cohort effects in psychological and behavioral outcomes in people living with hiv the french cross sectional anrs vespa2 survey
BMC Public Health, 2019Co-Authors: Luis Sagaonteyssier, Antoine Vilotitch, Marion Mora, Gwenaelle Maradan, Valerie Guagliardo, Marie Suzanmonti, Rosemary Drayspira, Bruno SpireAbstract:Unlike their younger counterparts, some of today’s older HIV patients were diagnosed before the advent of highly active antiretroviral therapy (HAART). The psychosocial and behavioral outcomes of people living with HIV (PLWH) have been widely studied, and associated factors are well known. However, their evolution both in terms of age and diagnosis-specific cohort effects is not well understood. Data from the ANRS-VESPA2 cross-sectional survey, representative of French PLWH, were used to investigate whether psychosocial and behavioral outcomes such as quality of life, need for support and HIV status disclosure, evolve under both the influence of patients’ age and diagnosis-specific cohort effects. A semi-parametric Generalized Additive Model (GAM) was employed. The physical and mental components of health-related quality of life, the need for material and moral support, and HIV-status disclosure, constituted our outcomes. Non-linear diagnosis-specific cohort effects were found for physical and mental QoL and HIV-status disclosure. Overall, physical QoL was better in recently diagnosed patients than in those diagnosed in the early 1980s. An increasing influence of diagnosis-specific cohort effects between 1983 and 1995 was observed. No cohort effects were noticeable between 1996 and 2000, while an increasing influence was apparent for patients diagnosed with HIV from 2000 to 2011 (year of study). For mental QoL, the only increase was observed in participants diagnosed with HIV between 1983 and 2000. The relationship between diagnosis-specific cohort effects and HIV status disclosure was negative overall: participants diagnosed after 2000 were much less likely to disclose than those diagnosed before 1995. The effect of age was significantly associated with all outcomes, with a non-linear influence on mental QoL and with the need for material/moral support. Psychosocial and behavioral outcomes are complex processes which can be explained in different ways by a combination of the clinical and social contexts which PLWH are exposed to at the time of diagnosis, and by developmental characteristics. A greater understanding of these processes could inform healthcare policy-making for specific HIV generations and different HIV age groups.
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A Generalized Additive Model to disentangle age and diagnosis-specific cohort effects in psychological and behavioral outcomes in people living with HIV: the French cross-sectional ANRS-VESPA2 survey
BMC Public Health, 2019Co-Authors: Luis Sagaon-teyssier, Antoine Vilotitch, Marion Mora, Gwenaelle Maradan, Valerie Guagliardo, Marie Suzan-monti, Rosemary Dray-spira, Bruno SpireAbstract:BACKGROUND: Unlike their younger counterparts, some of today's older HIV patients were diagnosed before the advent of highly active antiretroviral therapy (HAART). The psychosocial and behavioral outcomes of people living with HIV (PLWH) have been widely studied, and associated factors are well known. However, their evolution both in terms of age and diagnosis-specific cohort effects is not well understood. METHODS: Data from the ANRS-VESPA2 cross-sectional survey, representative of French PLWH, were used to investigate whether psychosocial and behavioral outcomes such as quality of life, need for support and HIV status disclosure, evolve under both the influence of patients' age and diagnosis-specific cohort effects. A semi-parametric Generalized Additive Model (GAM) was employed. The physical and mental components of health-related quality of life, the need for material and moral support, and HIV-status disclosure, constituted our outcomes. RESULTS: Non-linear diagnosis-specific cohort effects were found for physical and mental QoL and HIV-status disclosure. Overall, physical QoL was better in recently diagnosed patients than in those diagnosed in the early 1980s. An increasing influence of diagnosis-specific cohort effects between 1983 and 1995 was observed. No cohort effects were noticeable between 1996 and 2000, while an increasing influence was apparent for patients diagnosed with HIV from 2000 to 2011 (year of study). For mental QoL, the only increase was observed in participants diagnosed with HIV between 1983 and 2000. The relationship between diagnosis-specific cohort effects and HIV status disclosure was negative overall: participants diagnosed after 2000 were much less likely to disclose than those diagnosed before 1995. The effect of age was significantly associated with all outcomes, with a non-linear influence on mental QoL and with the need for material/moral support. CONCLUSIONS: Psychosocial and behavioral outcomes are complex processes which can be explained in different ways by a combination of the clinical and social contexts which PLWH are exposed to at the time of diagnosis, and by developmental characteristics. A greater understanding of these processes could inform healthcare policy-making for specific HIV generations and different HIV age groups.
Luis Sagaonteyssier - One of the best experts on this subject based on the ideXlab platform.
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a Generalized Additive Model to disentangle age and diagnosis specific cohort effects in psychological and behavioral outcomes in people living with hiv the french cross sectional anrs vespa2 survey
BMC Public Health, 2019Co-Authors: Luis Sagaonteyssier, Antoine Vilotitch, Marion Mora, Gwenaelle Maradan, Valerie Guagliardo, Marie Suzanmonti, Rosemary Drayspira, Bruno SpireAbstract:Unlike their younger counterparts, some of today’s older HIV patients were diagnosed before the advent of highly active antiretroviral therapy (HAART). The psychosocial and behavioral outcomes of people living with HIV (PLWH) have been widely studied, and associated factors are well known. However, their evolution both in terms of age and diagnosis-specific cohort effects is not well understood. Data from the ANRS-VESPA2 cross-sectional survey, representative of French PLWH, were used to investigate whether psychosocial and behavioral outcomes such as quality of life, need for support and HIV status disclosure, evolve under both the influence of patients’ age and diagnosis-specific cohort effects. A semi-parametric Generalized Additive Model (GAM) was employed. The physical and mental components of health-related quality of life, the need for material and moral support, and HIV-status disclosure, constituted our outcomes. Non-linear diagnosis-specific cohort effects were found for physical and mental QoL and HIV-status disclosure. Overall, physical QoL was better in recently diagnosed patients than in those diagnosed in the early 1980s. An increasing influence of diagnosis-specific cohort effects between 1983 and 1995 was observed. No cohort effects were noticeable between 1996 and 2000, while an increasing influence was apparent for patients diagnosed with HIV from 2000 to 2011 (year of study). For mental QoL, the only increase was observed in participants diagnosed with HIV between 1983 and 2000. The relationship between diagnosis-specific cohort effects and HIV status disclosure was negative overall: participants diagnosed after 2000 were much less likely to disclose than those diagnosed before 1995. The effect of age was significantly associated with all outcomes, with a non-linear influence on mental QoL and with the need for material/moral support. Psychosocial and behavioral outcomes are complex processes which can be explained in different ways by a combination of the clinical and social contexts which PLWH are exposed to at the time of diagnosis, and by developmental characteristics. A greater understanding of these processes could inform healthcare policy-making for specific HIV generations and different HIV age groups.
Daniel Morenofernandez - One of the best experts on this subject based on the ideXlab platform.
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Modeling sapling distribution over time using a functional predictor in a Generalized Additive Model
Annals of Forest Science, 2018Co-Authors: Nicole H. Augustin, Fernando Montes, Isabel Cañellas, Daniel Morenofernandez, Mariola SanchezgonzalezAbstract:Key message The effect of adult trees on sapling density distribution during the regeneration fellings is determined in a Pinus sylvestris L. Mediterranean forest using Generalized Additive Models.
Rosemary Drayspira - One of the best experts on this subject based on the ideXlab platform.
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a Generalized Additive Model to disentangle age and diagnosis specific cohort effects in psychological and behavioral outcomes in people living with hiv the french cross sectional anrs vespa2 survey
BMC Public Health, 2019Co-Authors: Luis Sagaonteyssier, Antoine Vilotitch, Marion Mora, Gwenaelle Maradan, Valerie Guagliardo, Marie Suzanmonti, Rosemary Drayspira, Bruno SpireAbstract:Unlike their younger counterparts, some of today’s older HIV patients were diagnosed before the advent of highly active antiretroviral therapy (HAART). The psychosocial and behavioral outcomes of people living with HIV (PLWH) have been widely studied, and associated factors are well known. However, their evolution both in terms of age and diagnosis-specific cohort effects is not well understood. Data from the ANRS-VESPA2 cross-sectional survey, representative of French PLWH, were used to investigate whether psychosocial and behavioral outcomes such as quality of life, need for support and HIV status disclosure, evolve under both the influence of patients’ age and diagnosis-specific cohort effects. A semi-parametric Generalized Additive Model (GAM) was employed. The physical and mental components of health-related quality of life, the need for material and moral support, and HIV-status disclosure, constituted our outcomes. Non-linear diagnosis-specific cohort effects were found for physical and mental QoL and HIV-status disclosure. Overall, physical QoL was better in recently diagnosed patients than in those diagnosed in the early 1980s. An increasing influence of diagnosis-specific cohort effects between 1983 and 1995 was observed. No cohort effects were noticeable between 1996 and 2000, while an increasing influence was apparent for patients diagnosed with HIV from 2000 to 2011 (year of study). For mental QoL, the only increase was observed in participants diagnosed with HIV between 1983 and 2000. The relationship between diagnosis-specific cohort effects and HIV status disclosure was negative overall: participants diagnosed after 2000 were much less likely to disclose than those diagnosed before 1995. The effect of age was significantly associated with all outcomes, with a non-linear influence on mental QoL and with the need for material/moral support. Psychosocial and behavioral outcomes are complex processes which can be explained in different ways by a combination of the clinical and social contexts which PLWH are exposed to at the time of diagnosis, and by developmental characteristics. A greater understanding of these processes could inform healthcare policy-making for specific HIV generations and different HIV age groups.
