Model development including interactions with multiple imputed data

Abstract Background Multiple imputation is a reliable tool to deal with missing data and is becoming increasingly popular in biostatistics. However, building a model with interactions that are not specified a priori, in the presence of missing data, presents a challenge. On the one hand, the interactions are needed to impute the data, while on the other hand, the data is needed to identify the interactions. The objective of this study was to present a way in which this challenge can be addressed. Methods This paper investigates two strategies in which model development with interactions is achieved using a single data set generated from the Expectation Maximization (EM) algorithm. Imputation using both the fully conditional specification approach and the multivariate normal approach is carried out and results are compared. The strategies are illustrated with data from a study of ambient pollution and childhood asthma in Durban, South Africa. Results The different approaches to model building and imputation yielded similar results despite the data being mainly categorical. Both strategies investigated for building the model using the multivariate normal imputed data resulted in the identical set of variables and interactions being identified; while models built using data imputed by fully conditional specification were marginally different for the two strategies. It was found that, for both imputation approaches, model building with backward elimination applied to the initial EM data set was easier to implement, and produced good results, compared to those from a complete case analysis. Conclusions Developing a predictive model including interactions with data that suffers from missingness is easily done by identifying significant interactions and then applying backward elimination to a single data set imputed from the EM algorithm. It is hoped that this idea can be further developed and, by addressing this practical dilemma, there will be increased adoption of multiple imputation in medical research when data suffers from missingness.http://deepblue.lib.umich.edu/bitstream/2027.42/110125/1/12874_2014_Article_1145.pd

Hypertension: Development of a prediction model to adjust self-reported hypertension prevalence at the community level

Abstract Background Accurate estimates of hypertension prevalence are critical for assessment of population health and for planning and implementing prevention and health care programs. While self-reported data is often more economically feasible and readily available compared to clinically measured HBP, these reports may underestimate clinical prevalence to varying degrees. Understanding the accuracy of self-reported data and developing prediction models that correct for underreporting of hypertension in self-reported data can be critical tools in the development of more accurate population level estimates, and in planning population-based interventions to reduce the risk of, or more effectively treat, hypertension. This study examines the accuracy of self-reported survey data in describing prevalence of clinically measured hypertension in two racially and ethnically diverse urban samples, and evaluates a mechanism to correct self-reported data in order to more accurately reflect clinical hypertension prevalence. Methods We analyze data from the Detroit Healthy Environments Partnership (HEP) Survey conducted in 2002 and the National Health and Nutrition Examination (NHANES) 2001–2002 restricted to urban areas and participants 25 years and older. We re-calibrate measures of agreement within the HEP sample drawing upon parameter estimates derived from the NHANES urban sample, and assess the quality of the adjustment proposed within the HEP sample. Results Both self-reported and clinically assessed prevalence of hypertension were higher in the HEP sample (29.7 and 40.1, respectively) compared to the NHANES urban sample (25.7 and 33.8, respectively). In both urban samples, self-reported and clinically assessed prevalence is higher than that reported in the full NHANES sample in the same year (22.9 and 30.4, respectively). Sensitivity, specificity and accuracy between clinical and self-reported hypertension prevalence were ‘moderate to good’ within the HEP sample and ‘good to excellent’ within the NHANES sample. Agreement between clinical and self-reported hypertension prevalence was ‘moderate to good’ within the HEP sample (kappa =0.65; 95% CI = 0.63-0.67), and ‘good to excellent’ within the NHANES sample (kappa = 0.75; 95%CI = 0.73-0.80). Application of a ‘correction’ rule based on prediction models for clinical hypertension using the national sample (NHANES) allowed us to re-calibrate sensitivity and specificity estimates for the HEP sample. The adjusted estimates of hypertension in the HEP sample based on two different correction models, 38.1% and 40.5%, were much closer to the observed hypertension prevalence of 40.1%. Conclusions Application of a simple prediction model derived from national NHANES data to self-reported data from the HEP (Detroit based) sample resulted in estimates that more closely approximated clinically measured hypertension prevalence in this urban community. Similar correction models may be useful in obtaining more accurate estimates of hypertension prevalence in other studies that rely on self-reported hypertension.http://deepblue.lib.umich.edu/bitstream/2027.42/112834/1/12913_2011_Article_2187.pd

El estrés crónico como mediador de la relación entre la posición socioeconómica y el cumplimiento del tratamiento farmacológico de pacientes hipertensos

Introduction: High blood pressure is a public health problem worldwide. In Colombia, its prevalence is 25% with a high mortality rate. The psychosocial factors affecting pharmacological adherence among patients have not been sufficiently studied and despite international evidence on their impact, in Colombia, there is a paucity of research on the role of chronic stress in the relationship between socioeconomic status and pharmacological adherence.Objective: To examine the role of chronic stress in the relationship between socioeconomic status and pharmacological adherence in hypertensive patients aged 45 to 70 years old in three Colombian cities between 2015 and 2016.Materials and methods: We conducted a cross-sectional study in a population of hypertensive patients. Data for this study came from the first wave of longitudinal study aimed at examining social factors associated with the control of hypertension in Bogotá, Medellín, and Quibdó. Patients with hypertension were selected randomly from a sample of those participating in the hypertension control program De todo corazón. For the statistical analysis of the data, we used factorial analysis and multivariate regressions.Results: We found a positive association between socioeconomic status and the degree of pharmacological adherence and a negative one with chronic stress. Besides, evidence was found that stress has a negative association with the degree of adherence.Conclusions: The results suggest that stress is not a likely mediator between socioeconomic status and the pharmacological adherence of hypertensive patients in Colombia. Additional studies are required to confirm these relationships with a larger sample.Introducción. La hipertensión arterial sistémica es un problema de salud pública en el mundo. En Colombia, su prevalencia es del 25 % y la mortalidad es alta. Los factores psicosociales que afectan el cumplimiento del tratamiento farmacológico no han sido estudiados suficientemente. En otros países, se ha estudiado el papel del estrés crónico en la relación entre la posición socioeconómica y el cumplimiento del tratamiento farmacológico antihipertensivo.Objetivo. Examinar el papel del estrés crónico como mediador de la relación entre la posición socioeconómica y el cumplimiento del tratamiento farmacológico, en pacientes hipertensos de 45 a 70 años en el 2015 y el 2016.Materiales y métodos. Se hizo un estudio transversal de una población de pacientes hipertensos. Los datos provienen de la muestra seleccionada para el programa “De todo corazón” en Bogotá, Medellín y Quibdó. El análisis estadístico de los datos se hizo mediante análisis factorial y regresiones multivariadas.Resultados. Los resultados confirmaron una asociación positiva entre la posición socioeconómica y el grado de cumplimiento del tratamiento farmacológico, y una relación negativa entre la primera y el estrés crónico. Además, se evidenció que el estrés tiene una asociación negativa con el grado de cumplimiento.Conclusiones. Los resultados sugieren que el estrés no es un mediador entre la posición socioeconómica y el cumplimiento del tratamiento farmacológico antihipertensivo en Colombia. Se requieren estudios adicionales para confirmar estas relaciones con una muestra más amplia

Accepted: 2011-10-04.) © SAJEI South Afr

Original Research: GGSTM1, GSTP1 and NQO1 polymorphisms and susceptibility to asthma among South African children Gluthathione-S-transferase (GSTM1 and GSTP1) and nicotinamide quinone oxidoreductase (NQO1) genes play an important role in cellular protection against oxidative stress, which has been linked to asthma pathogenesis. We investigated whether common, functional polymorphisms in GSTM1, GSTP1, and NQO1 influence susceptibility to asthma among schoolchildren in South Africa. Genomic deoxyribonucleic acid (DNA) was extracted from 317 primary schoolchildren, aged 9-11 years, from the urban, underprivileged socio-economic communities of Durban. GSTM1 (null vs. present genotype), GSTP1 (Ile105Val; AA →AG+GG) and the NQO1 (Pro/Ser; CC →CT/TT) genotypes were determined using polymerase chain reaction. Among the children, 30% were GSTM1 null, 65% carried the G allele for GSTP1, and 36% carried the C allele for NQO1.There was a high prevalence of asthma of any severity (46.1%), with 20.4% reporting persistent asthma. The GSTP1 AG+GG polymorphic genotype was significantly associated with persistent asthma (adjusted OR = 3.98; CI = 1.39, 11.36, p-value = 0.01). Neither the GSTM1, nor the NQO1, genotype was a significant predictor of persistent asthma. Therefore, the GSTP1 A/G variant may modulate the risk of persistent asthma among our sample

Air Pollution–Associated Changes in Lung Function among Asthmatic Children in Detroit

In a longitudinal cohort study of primary-school–age children with asthma in Detroit, Michigan, we examined relationships between lung function and ambient levels of particulate matter ≤ 10 μm and ≤ 2.5 μm in diameter (PM(10) and PM(2.5)) and ozone at varying lag intervals using generalized estimating equations. Models considered effect modification by maintenance corticosteroid (CS) use and by the presence of an upper respiratory infection (URI) as recorded in a daily diary among 86 children who participated in six 2-week seasonal assessments from winter 2001 through spring 2002. Participants were predominantly African American from families with low income, and > 75% were categorized as having persistent asthma. In both single-pollutant and two-pollutant models, many regressions demonstrated associations between higher exposure to ambient pollutants and poorer lung function (increased diurnal variability and decreased lowest daily values for forced expiratory volume in 1 sec) among children using CSs but not among those not using CSs, and among children reporting URI symptoms but not among those who did not report URIs. Our findings suggest that levels of air pollutants in Detroit, which are above the current National Ambient Air Quality Standards, adversely affect lung function of susceptible asthmatic children

Influence of viral infection on the relationships between airway cytokines and lung function in asthmatic children

Abstract Background Few longitudinal studies examine inflammation and lung function in asthma. We sought to determine the cytokines that reduce airflow, and the influence of respiratory viral infections on these relationships. Methods Children underwent home collections of nasal lavage during scheduled surveillance periods and self-reported respiratory illnesses. We studied 53 children for one year, analyzing 392 surveillance samples and 203 samples from 85 respiratory illnesses. Generalized estimated equations were used to evaluate associations between nasal lavage biomarkers (7 mRNAs, 10 proteins), lung function and viral infection. Results As anticipated, viral infection was associated with increased cytokines and reduced FVC and FEV1. However, we found frequent and strong interactions between biomarkers and virus on lung function. For example, in the absence of viral infection, CXCL10 mRNA, MDA5 mRNA, CXCL10, IL-4, IL-13, CCL4, CCL5, CCL20 and CCL24 were negatively associated with FVC. In contrast, during infection, the opposite relationship was frequently found, with IL-4, IL-13, CCL5, CCL20 and CCL24 levels associated with less severe reductions in both FVC and FEV1. Conclusions In asthmatic children, airflow obstruction is driven by specific pro-inflammatory cytokines. In the absence of viral infection, higher cytokine levels are associated with decreasing lung function. However, with infection, there is a reversal in this relationship, with cytokine abundance associated with reduced lung function decline. While nasal samples may not reflect lower airway responses, these data suggest that some aspects of the inflammatory response may be protective against viral infection. This study may have ramifications for the treatment of viral-induced asthma exacerbations.https://deepblue.lib.umich.edu/bitstream/2027.42/146519/1/12931_2018_Article_922.pd

Neighbourhood socioeconomic disadvantage and fruit and vegetable consumption:a seven countries comparison

BACKGROUND: Low fruit and vegetable consumption is a risk factor for poor health. Studies have shown consumption varies across neighbourhoods, with lower intakes in disadvantaged neighbourhoods. However, findings are inconsistent, suggesting that socio-spatial inequities in diet could be context-specific, highlighting a need for international comparisons across contexts. This study examined variations in fruit and vegetable consumption among adults from neighbourhoods of varying socioeconomic status (SES) across seven countries (Australia, Canada, Netherlands, New Zealand, Portugal, Scotland, US). METHODS: Data from seven existing studies, identified through literature searches and knowledge of co-authors, which collected measures of both neighbourhood-level SES and fruit and vegetable consumption were used. Logistic regression was used to examine associations between neighbourhood-level SES and binary fruit and vegetable consumption separately, adjusting for neighbourhood clustering and age, gender and education. As much as possible, variables were treated in a consistent manner in the analysis for each study to allow the identification of patterns of association within study and to examine differences in the associations across studies. RESULTS: Adjusted analyses showed evidence of an association between neighbourhood-level SES and fruit consumption in Canada, New Zealand and Scotland, with increased odds of greater fruit intake in higher SES neighbourhoods. In Australia, Canada, New Zealand and Portugal, those residing in higher SES neighbourhoods had increased odds of greater vegetable intake. The other studies showed no evidence of a difference by neighbourhood-level SES. CONCLUSIONS: Acknowledging discrepancies across studies in terms of sampling, measures, and definitions of neighbourhoods, this opportunistic study, which treated data in a consistent manner, suggests that associations between diet and neighbourhood-level socioeconomic status vary across countries. Neighbourhood socioeconomic disadvantage may differentially impact on access to resources in which produce is available in different countries. Neighbourhood environments have the potential to influence behaviour and further research is required to examine the context in which these associations arise

Longitudinal data analysis using growth curve models.

Growth curve analysis is useful in studies with repeated measurements on experimental units. They enable one to fit a response curve over the levels of a repeated factor, this response curve then is useful for prediction purposes. The first part of this dissertation considers a generalization of the Potthoff-Roy growth curve model. It combines two previous extensions, the sum of profiles model (Patel (1986), Verbyla (1988), Bandekar (1998)), and the exchangeably distributed errors model (Weissfield and Kshirsagar (1992)). We present a method of estimating growth curve coefficients of such model, using the method of least squares, as in multivariate regression. This also becomes identical to the method of restricted maximum likelihood. We provide explicit expressions for these estimates and their standard errors, unlike Patel (1986) and Verbyla (1988). Some hypothesis testing problems are considered for these coefficients. We reduce the model with exchangeably distributed error to two independent models, by orthogonal transformation and augmentation of the design matrix. One model takes into account group contrasts and the other a kind of average group effect. The second part of this dissertation is concerned with the use of growth curve models for classification purposes. We have developed allocation rules for data that have structured means as well as structured covariance matrices, we provide an estimate for the chance of misclassification. When the means of the different groups have a Potthoff-Roy type structure, certain linear combinations of the feature variables have zero means. These are not useful for classification and should be removed to reduce the chance of misclassification. We derive allocation rules based on Rao's (1973) scores for two different scenarios: (1) When the variance-covariance matrix is known and assumed to be compound symmetric, and no model-based covariates are included in the allocation rule, and (2) when the covariance structure is unknown. For this second case, we have studied the importance of including or excluding model-based covariates in the allocation rule, and their influence on the misclassification rate. An important contribution of this dissertation is to provide the chance of misclassification using these new allocation rules.Ph.D.Pure SciencesStatisticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123445/2/3079500.pd

The relationship of built environment to health-related behaviors and health outcomes in elderly community residents in a middle income country

<em>Background</em>. Few studies have examined the impact of the built environment (BE) on health behaviours and health outcomes in middle income countries. This study examines associations between self-assessed characteristics of the home and neighbourhood environment and health-related behaviours and health outcomes in an elderly population in Brazil.<br /> <em>Design and methods.</em> In a community sample of 6963 community dwellers 60 years old and older living in the state of Rio Grande do Sul, Brazil, associations between self-reported BE conditions and health behaviours and health outcomes were assessed using a structured questionnaire. Multivariate analysis was conducted to investigate these associations while accounting for other relevant characteristics. <br /><em>Results</em>. We found significant positive associations between adverse BE conditions and pulmonary, urinary conditions, gastrointestinal, problems, headache and depression. There were mixed associations between adverse BE conditions and musculoskeletal and sensory conditions, inverse associations with metabolic disorders. and no associations with dermatologic problems and cancer. After accounting for health related behaviours, results suggest a modest association between adverse BE conditions and hypertension, with no significant associations with other indicators of cardiovascular conditions (heart problems, stroke, varicose veins).<br /><em>Conclusions</em>. The findings in this study suggest links between adverse conditions in the BE and health related behaviours in the hypothesized direction. Associations with the health conditions examined here are mixed. We find the strongest evidence for effects of adverse BE conditions for pulmonary and infectious conditions. Significant associations between the adverse BE indicators and health outcomes persist after accounting for health related behaviours, suggesting that BE conditions are linked to health pathways above and beyond the health related behaviours assessed in this study

Asociación entre marcadores de posición social y adherencia al tratamiento de la hipertensión arterial en Colombia

Introduction: To generate evidence on the effects of social position on therapeutic adherence among individuals with hypertension (HT) in Colombia. Materials and Methods: A cross-sectional study was carried out, using quantitative data from the Social Determinants and Inequities in the Control of HT Program in Colombia. Descriptive and inferential analyses (logistic regression) were developed to model the associations. Results: The prevalence of adherence was high, especially for pharmacological treat¬ment and compliance with appointments (>50%). Individuals with less education and lower income are less likely to adhere to pharmacological treatment, while tho¬se with higher socioeconomic status are less likely to adhere to appointments and healthy behaviors. Afro-Colombians were less likely to adhere to pharmacological treatment, appointments, and indications regarding physical activity. Discussion: There is a gap in HT treatment adherence in Colombia, due to socioeco¬nomic and ethnic/racial conditionIntroducción: Generar evidencia sobre los efectos de la posición social en la adhe¬rencia terapéutica en personas con hipertensión arterial (HTA) en Colombia. Materiales y Métodos: Se realizó un estudio transversal, a partir de mediciones cuan¬titativas del Programa de Determinantes Sociales e Inequidades en el Control de la HTA en Colombia. Se desarrollaron análisis descriptivos e inferenciales (regresión logística) para modelar las asociaciones. Resultados: Se evidenció una alta proporción de adherencia, siendo mayor para cumplimiento farmacológico y las citas (>50%). Las personas con menor educación e ingresos tienen menor posibilidad de adherirse al tratamiento farmacológico; mien¬tras que quienes tienen mejor posición socioeconómica tienen menor posibilidad de adherirse a las citas y a las conductas saludables. Los afrocolombianos tienen menor posibilidad de adherirse al tratamiento farmacológico, a las citas y a la actividad física. Discusión: Existe una brecha en el logro de la adherencia a tratamiento de HTA en Colombia, debido a condiciones socioeconómicas y étnica/raciales