DG Chen - Academia.edu (original) (raw)
Papers by DG Chen
The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 2012
Objectives. To characterize the trajectories of laboratory-and real world-based speed of processi... more Objectives. To characterize the trajectories of laboratory-and real world-based speed of processing (SOP) over 5 years using finite latent growth mixture modeling, and to explore associated baseline individual-level predictors and functional outcomes in 2,802 community-dwelling older adults from the Advanced Cognitive Training for Independent and Vital Elderly cohort. Method. Laboratory-and real world-based SOP and functional outcomes were assessed over 5 years, and candidate individual-level predictors were collected at baseline. Results. After controlling for intervention assignment and demographic information, 4 distinct trajectories were identified: 4.6% of older adults had poor laboratory-based SOP and very poor real world-based SOP that both declined substantially over time; 17.9% had poor laboratory-and real world-based SOP that declined moderately; 38.7% had neutral laboratory-and real world-based SOP that maintained stable; and 37.9% had good laboratory-and real world-based SOP that declined slightly. Non-White, depression, subjective memory complaints, and vascular factors predicted the trajectories. The trajectories significantly differed in the rate of decline in basic activities of daily living, instrumental activities of daily living, and grip strength over time. Discussion. Heterogeneous trajectories of SOP exist in old age. Future interventions addressing SOP should target the vulnerable group with poor SOP over time.
At the eleventh annual meeting of the North Pacific Anadromous Fish Commission in 2003, the Worki... more At the eleventh annual meeting of the North Pacific Anadromous Fish Commission in 2003, the Working Group on Stock Assessment discussed the possibility of assembling data other than catch to assess the status of salmon. In this report we apply a consistent analytical approach to several data types frequently used to index Pacific salmon in Canada. We compare results using different data types by examining the influence of three recent regime shifts. Conclusions from our evaluation of effects from the 1977 and 1989 regime shifts depended on which of three salmon abundance indices (catch, escapement, and total returns) and two survival indices (marine survival and recruits per spawner) were used. For instance, abundance shifts did not necessarily correspond with changes in survival, and regional variations existed, at least for coho. Results from our analysis confirm that different interpretations of salmon "status" may result, depending on which index is used.
Canadian Journal of Fisheries and Aquatic Sciences, 2001
A novel semiparametric model that can incorporate environmental and fishery data is developed to ... more A novel semiparametric model that can incorporate environmental and fishery data is developed to analyze stock-recruitment relationships. Unlike traditional stock-recruitment models that assume a log-linear relationship between recruitment and environmental and fishery variables, the new model uses a nonparametric smoothing algorithm, which helps quantify the underlying empirical relationships and enables more accurate parameter estimates. Bootstrap resampling is used to evaluate uncertainties in the model parameters. Distribution plots can be produced for stockrecruitment productivity and capacity parameters. This approach is applied to southeast Alaska pink salmon (Oncorhynchus gorbuscha) with sea surface temperature as the environmental variable and West Coast Vancouver Island herring (Clupea harengus) with sea surface temperature and hake biomass as two environmental variables. Results from diagnostic tests indicate that our model performed better than the traditional Ricker model and a Ricker model that was extended to include environmental effects. Résumé : On trouvera ici un nouveau modèle semiparamétrique capable d'incorporer les données environnementales et halieutiques dans l'analyse des relations entre le stock et le recrutement. À l'opposé des modèles traditionnels de stock-recrutement qui posent au départ l'existence d'une relation log-linéaire entre le recrutement et les variables environnementales et halieutiques, le nouveau modèle utilise un algorithme non-paramétrique de lissage qui aide à quantifier les relations empiriques sous-jacentes et permet une estimation plus précise des paramètres. Le ré-échantillonnage par bootstrap sert à évaluer les incertitudes dans les paramètres du modèle. Des diagrammes de dispersion peuvent être générés pour les paramètres de productivité et de capacité du modèle stock-recrutement. Le modèle est appliqué à une population de Saumons roses du sud-est de l'Alaska (Oncorhynchus gorbuscha) avec la température de surface de la mer comme variable environnementale, ainsi qu'à une population de harengs de la côte occidentale de l'Île de Vancouver (Clupea harengus) où la température de surface de la mer et la biomasse des merlus sont les variables environnementales. Des tests diagnostics révèlent que le nouveau modèle fonctionne mieux que le modèle traditionnel de Ricker et qu'un modèle de Ricker modifié de façon à inclure les effets de l'environnement.
2007 IEEE International Conference on Systems, Man and Cybernetics, 2007
In fuzzy rough sets a fuzzy T-similarity relation is employed to describe the similarity degree b... more In fuzzy rough sets a fuzzy T-similarity relation is employed to describe the similarity degree between two objects and to construct lower and upper approximations for arbitrary fuzzy sets. Different triangular norm T identifies different point of view of similarity. Thus a reasonable selection of triangular norm is meaningful to practical applications of fuzzy rough sets. In this paper we
Ecological Informatics, 2003
Zhongguo yao li xue bao = Acta pharmacologica Sinica, 1993
Effects of clonidine (Clo) on female reproductive system were studied in rats. Blood FSH, LH, pro... more Effects of clonidine (Clo) on female reproductive system were studied in rats. Blood FSH, LH, progesterone, testosterone, and estradiol were measured by radioimmunoassay and the development of secondary follicles and corpus luteum in ovary were investigated by morphometry. After Clo po 0.3 mg.kg-1.d-1 x 14 d, the estrus of rats was prolonged; FSH, LH, and progesterone increased significantly; while estradiol reduced. The development of secondary follicles in ovary was blocked at the stage of prematuration and the numerical density of corpus luteum decreased. After clonidine po 28 d, FSH and LH sustained at high levels, but the estrous cycle, estradiol and progesterone recovered.
Journal of Biopharmaceutical Statistics, 2007
In toxicological and pharmaceutical experiments, a type of quantal bioassay experiment is designe... more In toxicological and pharmaceutical experiments, a type of quantal bioassay experiment is designed in which a response, such as mortality, in a group of animals is recorded over time points under different dose levels in the course of the experiment. The application of the typical logit and probit analyses is no longer valid in this situation because it neglects the dependency on time and also the possible interaction of time and dose concentration on the response in the experiment. In this paper, a dose-time-response model is proposed for this type of experiment and a cumulative multinomial generalized linear model that incorporates time and the other experimental conditions as covariates is developed by the theory of maximum likelihood estimation. Both the point estimator and confidence bands for ED50(t), the concentration of a toxicant that will kill 50% of the animals by a specific time, t; as well as LT50(d), the time to 50% mortalities for a specific concentration, d, is then formulated in closed form from the newly proposed dose-time-response model. Finally, the newly proposed model is considered for a real data set to demonstrate the application.
Functional Materials Letters, 2012
A multiferroic heterostructure composed of ( Bi 0.875 Nd 0.125) FeO 3 (BNF) are grown on ( Ba 0.6... more A multiferroic heterostructure composed of ( Bi 0.875 Nd 0.125) FeO 3 (BNF) are grown on ( Ba 0.65 Sr 0.35) TiO 3(BST) buffered Pt/Ti/SiO2/Si(100) substrate by rf-magnetron sputtering. The heterostructure BNF/BST exhibits a quite low leakage current (3.7 × 10-7 A/cm2 at 300 kV/cm) and dielectric loss (0.0036 at 100 kHz) at room temperature. The saturated magnetization and the coercive field of the BST/BNF heterostructure are 37.7 emu/cm3 and 357.6 Oe, respectively. The low leakage current owed to the action of BST in the charge transfer between BNF and the bottom electrode, the coupling reaction between BST and BNF films. And the better crystallization in BNF/BST heterostructure thin film lead to the ferromagnetic properties enhanced.
Environmental Toxicology and Pharmacology, 2004
Scientific and societal interest in the analysis of aggregate toxicity derives from the fact that... more Scientific and societal interest in the analysis of aggregate toxicity derives from the fact that people are seldom exposed to single chemicals, but rather to multiple agents from different sources and even to mixtures of agents from a single source. Many descriptive terms and mathematical, graphical, and statistical models have been used to evaluate the toxicity of simple mixtures. It is not very easy to distinguish clearly the intrinsic differences, distinctions and limitations of these models when applied to characterizing interactive toxicity. A series of experiments were performed to illustrate model-dependent consistencies and differences in interactive toxicity. Cultured murine renal cortical cells, target cells for metal toxicity, were treated with selected concentrations of one metal or binary mixtures of metals to give conditions of dose-additivity, response additivity, or with only one toxic member of the binary mixture. The cytotoxicity was determined at 24 h by lactate dehydrogenase release. The data were analyzed graphically and mathematically by (a) Carter's statistical isobologram, (b) Barton's non-linear, and (c) Kodell and Pounds' linear models to characterize the interaction. These models were compared and contrasted for robustness, and consistency using these common data sets. The models gave generally consistent conclusions, but each model has limitations and strengths for assessing particular mixtures scenarios. This comparison illustrates the complexity of extrapolating conclusions between models, and difficulty of public health assessment from exposures to multiple chemicals in the environment.
Environmental Health Perspectives, 1998
The linear logistical isobologram is a commonly used and powerful graphical and statistical tool ... more The linear logistical isobologram is a commonly used and powerful graphical and statistical tool for analyzing the combined effects of simple chemical mixtures. In this paper a nonlinear isobologram model is proposed to analyze the joint action of chemical mixtures for quantitative dose-response relationships. This nonlinear isobologram model incorporates two additional new parameters, Ymin and Ymax, to facilitate analysis of response data that are not constrained between 0 and 1, where parameters Ymin and Ymax represent the minimal and the maximal observed toxic response. This nonlinear isobologram model for binary mixtures can be expressed as: Y = Ymin + Ymax Ymin i + e-(po+3ldl+p2d2+/12d1d2) In addition, a Box-Cox transformation to both sides is introduced to improve the goodness of fit and to provide a more robust model for achieving homogeneity and normality of the residuals. Finally, a confidence band is proposed for selected isobols, e.g., the median effective dose, to facilitate graphical and statistical analysis of the isobologram. The versatility of this approach is demonstrated using published data describing the toxicity of the binary mixtures of citrinin and ochratoxin as well as a new experimental data from our laboratory for mixtures of mercury and cadmium.
Canadian Journal of Fisheries and Aquatic Sciences, 1999
A neural network model is developed to forecast the recruiting biomass of fish. The west coast of... more A neural network model is developed to forecast the recruiting biomass of fish. The west coast of Vancouver Island, British Columbia, Pacific herring (Clupea pallasi) stock is selected as an example application based on data compiled from long-term ecosystem research and stock assessment programs. A fuzzy logic decision procedure was used to evaluate all possible neural networks. The output from the two "optimal" networks was compared with the output from a multiple regression analysis and a standard Ricker climate stock-recruitment model. The performance of the neural network models in reproducing a 41-year time series was far superior (R2 between the fitted and observed recruitment is about 60-70%) to the multiple linear regression model (R2 = 0.29) and the Ricker climate stock-recruitment model (R2 = 42%). This pilot study demonstrates how artificial neural networks can be used to improve the accuracy of fishery stock forecasts and hence the management of the fishery re...
Biometrics, 1999
This article presents a new empirical Bayes estimator (EBE) and a shrinkage estimator for determi... more This article presents a new empirical Bayes estimator (EBE) and a shrinkage estimator for determining the relative potency from several multivariate bioassays by incorporating prior information on the model parameters based on Jeffreys&amp;#39; rules. The EBE can account for any extra variability among the bioassays, and if this extra variability is 0, then the EBE reduces to the maximum likelihood estimator for combinations of multivariate bioassays. The shrinkage estimator turns out to be a compromise of the prior information and the estimator from each multivariate bioassay, with the weights depending on the prior variance.
The Journal of Clinical Endocrinology & Metabolism, 2010
Black women have lower 25-hydroxyvitamin D [25(OH)D] and higher PTH than white women. Recent evid... more Black women have lower 25-hydroxyvitamin D [25(OH)D] and higher PTH than white women. Recent evidence implicates PTH in adverse cardiovascular outcomes. Objective: The objective of the study was to determine whether PTH increases at lower 25(OH)D levels (the threshold) in black compared with white women. Design: Healthy black and white women, aged 20-80 yr were recruited to participate in a crosssectional study of body-composition in black and white women. Measurement of serum 25(OH)D and PTH were carried out. Setting: The study was a convenience sample recruited from a community setting. Patients: Healthy black and white women were recruited by advertising and a direct mail campaign in a comparative study of body composition. Age ranged from 20-to 80 yr. There were 148 black and 129 white premenopausal participants and 87 black and 139 white postmenopausal participants. Main Outcome: The main outcome was to determine whether the threshold for 25(OH)D/PTH differs in black and white women. Results: A threshold of 37 nmol/liter (95% confidence interval 35-40) was found for black and 59 nmol/liter (95% confidence interval 56-63) for white women. These two values were significantly different (P Ͻ 0.001). Conclusions: Black women have an increase in serum PTH at a lower 25(OH)D level than white women. Negative health outcomes of higher PTH should be investigated in black women.
Journal of Biometrics & Biostatistics, 2015
The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 2012
Objectives. To characterize the trajectories of laboratory-and real world-based speed of processi... more Objectives. To characterize the trajectories of laboratory-and real world-based speed of processing (SOP) over 5 years using finite latent growth mixture modeling, and to explore associated baseline individual-level predictors and functional outcomes in 2,802 community-dwelling older adults from the Advanced Cognitive Training for Independent and Vital Elderly cohort. Method. Laboratory-and real world-based SOP and functional outcomes were assessed over 5 years, and candidate individual-level predictors were collected at baseline. Results. After controlling for intervention assignment and demographic information, 4 distinct trajectories were identified: 4.6% of older adults had poor laboratory-based SOP and very poor real world-based SOP that both declined substantially over time; 17.9% had poor laboratory-and real world-based SOP that declined moderately; 38.7% had neutral laboratory-and real world-based SOP that maintained stable; and 37.9% had good laboratory-and real world-based SOP that declined slightly. Non-White, depression, subjective memory complaints, and vascular factors predicted the trajectories. The trajectories significantly differed in the rate of decline in basic activities of daily living, instrumental activities of daily living, and grip strength over time. Discussion. Heterogeneous trajectories of SOP exist in old age. Future interventions addressing SOP should target the vulnerable group with poor SOP over time.
At the eleventh annual meeting of the North Pacific Anadromous Fish Commission in 2003, the Worki... more At the eleventh annual meeting of the North Pacific Anadromous Fish Commission in 2003, the Working Group on Stock Assessment discussed the possibility of assembling data other than catch to assess the status of salmon. In this report we apply a consistent analytical approach to several data types frequently used to index Pacific salmon in Canada. We compare results using different data types by examining the influence of three recent regime shifts. Conclusions from our evaluation of effects from the 1977 and 1989 regime shifts depended on which of three salmon abundance indices (catch, escapement, and total returns) and two survival indices (marine survival and recruits per spawner) were used. For instance, abundance shifts did not necessarily correspond with changes in survival, and regional variations existed, at least for coho. Results from our analysis confirm that different interpretations of salmon "status" may result, depending on which index is used.
Canadian Journal of Fisheries and Aquatic Sciences, 2001
A novel semiparametric model that can incorporate environmental and fishery data is developed to ... more A novel semiparametric model that can incorporate environmental and fishery data is developed to analyze stock-recruitment relationships. Unlike traditional stock-recruitment models that assume a log-linear relationship between recruitment and environmental and fishery variables, the new model uses a nonparametric smoothing algorithm, which helps quantify the underlying empirical relationships and enables more accurate parameter estimates. Bootstrap resampling is used to evaluate uncertainties in the model parameters. Distribution plots can be produced for stockrecruitment productivity and capacity parameters. This approach is applied to southeast Alaska pink salmon (Oncorhynchus gorbuscha) with sea surface temperature as the environmental variable and West Coast Vancouver Island herring (Clupea harengus) with sea surface temperature and hake biomass as two environmental variables. Results from diagnostic tests indicate that our model performed better than the traditional Ricker model and a Ricker model that was extended to include environmental effects. Résumé : On trouvera ici un nouveau modèle semiparamétrique capable d'incorporer les données environnementales et halieutiques dans l'analyse des relations entre le stock et le recrutement. À l'opposé des modèles traditionnels de stock-recrutement qui posent au départ l'existence d'une relation log-linéaire entre le recrutement et les variables environnementales et halieutiques, le nouveau modèle utilise un algorithme non-paramétrique de lissage qui aide à quantifier les relations empiriques sous-jacentes et permet une estimation plus précise des paramètres. Le ré-échantillonnage par bootstrap sert à évaluer les incertitudes dans les paramètres du modèle. Des diagrammes de dispersion peuvent être générés pour les paramètres de productivité et de capacité du modèle stock-recrutement. Le modèle est appliqué à une population de Saumons roses du sud-est de l'Alaska (Oncorhynchus gorbuscha) avec la température de surface de la mer comme variable environnementale, ainsi qu'à une population de harengs de la côte occidentale de l'Île de Vancouver (Clupea harengus) où la température de surface de la mer et la biomasse des merlus sont les variables environnementales. Des tests diagnostics révèlent que le nouveau modèle fonctionne mieux que le modèle traditionnel de Ricker et qu'un modèle de Ricker modifié de façon à inclure les effets de l'environnement.
2007 IEEE International Conference on Systems, Man and Cybernetics, 2007
In fuzzy rough sets a fuzzy T-similarity relation is employed to describe the similarity degree b... more In fuzzy rough sets a fuzzy T-similarity relation is employed to describe the similarity degree between two objects and to construct lower and upper approximations for arbitrary fuzzy sets. Different triangular norm T identifies different point of view of similarity. Thus a reasonable selection of triangular norm is meaningful to practical applications of fuzzy rough sets. In this paper we
Ecological Informatics, 2003
Zhongguo yao li xue bao = Acta pharmacologica Sinica, 1993
Effects of clonidine (Clo) on female reproductive system were studied in rats. Blood FSH, LH, pro... more Effects of clonidine (Clo) on female reproductive system were studied in rats. Blood FSH, LH, progesterone, testosterone, and estradiol were measured by radioimmunoassay and the development of secondary follicles and corpus luteum in ovary were investigated by morphometry. After Clo po 0.3 mg.kg-1.d-1 x 14 d, the estrus of rats was prolonged; FSH, LH, and progesterone increased significantly; while estradiol reduced. The development of secondary follicles in ovary was blocked at the stage of prematuration and the numerical density of corpus luteum decreased. After clonidine po 28 d, FSH and LH sustained at high levels, but the estrous cycle, estradiol and progesterone recovered.
Journal of Biopharmaceutical Statistics, 2007
In toxicological and pharmaceutical experiments, a type of quantal bioassay experiment is designe... more In toxicological and pharmaceutical experiments, a type of quantal bioassay experiment is designed in which a response, such as mortality, in a group of animals is recorded over time points under different dose levels in the course of the experiment. The application of the typical logit and probit analyses is no longer valid in this situation because it neglects the dependency on time and also the possible interaction of time and dose concentration on the response in the experiment. In this paper, a dose-time-response model is proposed for this type of experiment and a cumulative multinomial generalized linear model that incorporates time and the other experimental conditions as covariates is developed by the theory of maximum likelihood estimation. Both the point estimator and confidence bands for ED50(t), the concentration of a toxicant that will kill 50% of the animals by a specific time, t; as well as LT50(d), the time to 50% mortalities for a specific concentration, d, is then formulated in closed form from the newly proposed dose-time-response model. Finally, the newly proposed model is considered for a real data set to demonstrate the application.
Functional Materials Letters, 2012
A multiferroic heterostructure composed of ( Bi 0.875 Nd 0.125) FeO 3 (BNF) are grown on ( Ba 0.6... more A multiferroic heterostructure composed of ( Bi 0.875 Nd 0.125) FeO 3 (BNF) are grown on ( Ba 0.65 Sr 0.35) TiO 3(BST) buffered Pt/Ti/SiO2/Si(100) substrate by rf-magnetron sputtering. The heterostructure BNF/BST exhibits a quite low leakage current (3.7 × 10-7 A/cm2 at 300 kV/cm) and dielectric loss (0.0036 at 100 kHz) at room temperature. The saturated magnetization and the coercive field of the BST/BNF heterostructure are 37.7 emu/cm3 and 357.6 Oe, respectively. The low leakage current owed to the action of BST in the charge transfer between BNF and the bottom electrode, the coupling reaction between BST and BNF films. And the better crystallization in BNF/BST heterostructure thin film lead to the ferromagnetic properties enhanced.
Environmental Toxicology and Pharmacology, 2004
Scientific and societal interest in the analysis of aggregate toxicity derives from the fact that... more Scientific and societal interest in the analysis of aggregate toxicity derives from the fact that people are seldom exposed to single chemicals, but rather to multiple agents from different sources and even to mixtures of agents from a single source. Many descriptive terms and mathematical, graphical, and statistical models have been used to evaluate the toxicity of simple mixtures. It is not very easy to distinguish clearly the intrinsic differences, distinctions and limitations of these models when applied to characterizing interactive toxicity. A series of experiments were performed to illustrate model-dependent consistencies and differences in interactive toxicity. Cultured murine renal cortical cells, target cells for metal toxicity, were treated with selected concentrations of one metal or binary mixtures of metals to give conditions of dose-additivity, response additivity, or with only one toxic member of the binary mixture. The cytotoxicity was determined at 24 h by lactate dehydrogenase release. The data were analyzed graphically and mathematically by (a) Carter's statistical isobologram, (b) Barton's non-linear, and (c) Kodell and Pounds' linear models to characterize the interaction. These models were compared and contrasted for robustness, and consistency using these common data sets. The models gave generally consistent conclusions, but each model has limitations and strengths for assessing particular mixtures scenarios. This comparison illustrates the complexity of extrapolating conclusions between models, and difficulty of public health assessment from exposures to multiple chemicals in the environment.
Environmental Health Perspectives, 1998
The linear logistical isobologram is a commonly used and powerful graphical and statistical tool ... more The linear logistical isobologram is a commonly used and powerful graphical and statistical tool for analyzing the combined effects of simple chemical mixtures. In this paper a nonlinear isobologram model is proposed to analyze the joint action of chemical mixtures for quantitative dose-response relationships. This nonlinear isobologram model incorporates two additional new parameters, Ymin and Ymax, to facilitate analysis of response data that are not constrained between 0 and 1, where parameters Ymin and Ymax represent the minimal and the maximal observed toxic response. This nonlinear isobologram model for binary mixtures can be expressed as: Y = Ymin + Ymax Ymin i + e-(po+3ldl+p2d2+/12d1d2) In addition, a Box-Cox transformation to both sides is introduced to improve the goodness of fit and to provide a more robust model for achieving homogeneity and normality of the residuals. Finally, a confidence band is proposed for selected isobols, e.g., the median effective dose, to facilitate graphical and statistical analysis of the isobologram. The versatility of this approach is demonstrated using published data describing the toxicity of the binary mixtures of citrinin and ochratoxin as well as a new experimental data from our laboratory for mixtures of mercury and cadmium.
Canadian Journal of Fisheries and Aquatic Sciences, 1999
A neural network model is developed to forecast the recruiting biomass of fish. The west coast of... more A neural network model is developed to forecast the recruiting biomass of fish. The west coast of Vancouver Island, British Columbia, Pacific herring (Clupea pallasi) stock is selected as an example application based on data compiled from long-term ecosystem research and stock assessment programs. A fuzzy logic decision procedure was used to evaluate all possible neural networks. The output from the two "optimal" networks was compared with the output from a multiple regression analysis and a standard Ricker climate stock-recruitment model. The performance of the neural network models in reproducing a 41-year time series was far superior (R2 between the fitted and observed recruitment is about 60-70%) to the multiple linear regression model (R2 = 0.29) and the Ricker climate stock-recruitment model (R2 = 42%). This pilot study demonstrates how artificial neural networks can be used to improve the accuracy of fishery stock forecasts and hence the management of the fishery re...
Biometrics, 1999
This article presents a new empirical Bayes estimator (EBE) and a shrinkage estimator for determi... more This article presents a new empirical Bayes estimator (EBE) and a shrinkage estimator for determining the relative potency from several multivariate bioassays by incorporating prior information on the model parameters based on Jeffreys&amp;#39; rules. The EBE can account for any extra variability among the bioassays, and if this extra variability is 0, then the EBE reduces to the maximum likelihood estimator for combinations of multivariate bioassays. The shrinkage estimator turns out to be a compromise of the prior information and the estimator from each multivariate bioassay, with the weights depending on the prior variance.
The Journal of Clinical Endocrinology & Metabolism, 2010
Black women have lower 25-hydroxyvitamin D [25(OH)D] and higher PTH than white women. Recent evid... more Black women have lower 25-hydroxyvitamin D [25(OH)D] and higher PTH than white women. Recent evidence implicates PTH in adverse cardiovascular outcomes. Objective: The objective of the study was to determine whether PTH increases at lower 25(OH)D levels (the threshold) in black compared with white women. Design: Healthy black and white women, aged 20-80 yr were recruited to participate in a crosssectional study of body-composition in black and white women. Measurement of serum 25(OH)D and PTH were carried out. Setting: The study was a convenience sample recruited from a community setting. Patients: Healthy black and white women were recruited by advertising and a direct mail campaign in a comparative study of body composition. Age ranged from 20-to 80 yr. There were 148 black and 129 white premenopausal participants and 87 black and 139 white postmenopausal participants. Main Outcome: The main outcome was to determine whether the threshold for 25(OH)D/PTH differs in black and white women. Results: A threshold of 37 nmol/liter (95% confidence interval 35-40) was found for black and 59 nmol/liter (95% confidence interval 56-63) for white women. These two values were significantly different (P Ͻ 0.001). Conclusions: Black women have an increase in serum PTH at a lower 25(OH)D level than white women. Negative health outcomes of higher PTH should be investigated in black women.
Journal of Biometrics & Biostatistics, 2015