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Missing covariates

Miriam Krischke, Georg Hempel, Swantje Völler, Nicolas André, Maurizio D'Incalci, Gianni Bisogno, Wolfgang Köpcke, Matthias Borowski, Ralf Herold, Alan V Boddy, Joachim Boos
PURPOSE: Doxorubicin is a key component in many pediatric oncology treatment regimens; still pharmacology data on which current dosing regimens are based are very limited. METHODS: We conducted a multinational pharmacokinetic study investigating age dependency of doxorubicin metabolism and elimination in children with cancer. One hundred and one patients treated with doxorubicin according to a cancer-specific national or European therapeutic trial were recruited...
October 21, 2016: Cancer Chemotherapy and Pharmacology
Susan J Carson, Jacqueline Burns
DesignCohort studyCohort selectionParticipants were recruited between 1994 and 1998 from the general population with the preferred ages of 35 to 65 years in women and 40 to 65 years in men.Exposure measurementSmoking was assessed using a questionnaire from which pack years of smoking were calculated. Educational attainment, body mass index, hypertension, diabetes, alcohol consumption and vitamin or mineral supplements were assessed from measurements and questionnaires. Tooth loss was also assessed by questionnaire returned between 2004 and 2006...
September 2016: Evidence-based Dentistry
Stephen Harrap, Katrina Scurrah, Angela Lamantia, Justine Ellis
OBJECTIVE: Genes encoding key elements of the renin-angiotensin-aldosterone system (RAAS) cascade have been previously but inconsistently associated with blood pressure. Sex-dependency might be important here and functional genetic polymorphisms might exhibit epistatic effects. DESIGN AND METHOD: We assessed variation in the genes encoding renin (REN), angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin II type 1 receptor (AGTR1) and aldosterone synthase (CYP11B2)...
September 2016: Journal of Hypertension
Bruce C M Wang, Ping-Ning Hsu, Wesley Furnback, John Ney, Ya-Wen Yang, Chi-Hui Fang, Chao-Hsiun Tang
BACKGROUND: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by inflammation and destruction of the joints. OBJECTIVES: This research aims to estimate the economic burden of RA in Taiwan. METHODS: The National Health Insurance Research Database (NHIRD), a claims-based dataset encompassing 99 % of Taiwan's population, was applied. We used a micro-costing approach for direct healthcare costs and indirect social costs by estimating the quantities and prices of cost categories...
March 2016: Drugs—Real World Outcomes
Jacques P Maurissen, Thomas J Vidmar
Repeated-measure analysis of variance is a general term that can imply a number of different statistical models used to analyze data from studies in which measurements are taken from each subject on more than one occasion. Repeated-measure analyses encompass univariate models (with or without sphericity adjustment), multivariate models, mixed models, analysis of covariance, multilevel models, latent growth models, and hybrids of these models. These models are based on different assumptions, especially regarding correlations (sphericity) between within-subject factors, which comprise the variance-covariance matrix...
October 13, 2016: Neurotoxicology and Teratology
Sammy Chebon, Christel Faes, Frank Cools, Helena Geys
Statistical analysis of count data typically starts with a Poisson regression. However, in many real-life applications, it is observed that the variation in the counts is larger than the mean, and one needs to deal with the problem of overdispersion in the counts. Several factors may contribute to overdispersion: (1) unobserved heterogeneity due to missing covariates, (2) correlation between observations (such as in longitudinal studies), and (3) the occurrence of many zeros (more than expected from the Poisson distribution)...
October 13, 2016: Statistics in Medicine
Zhuoyu Wang, Nandini Dendukuri, Lawrence Joseph
When two imperfect diagnostic tests are carried out on the same subject, their results may be correlated even after conditioning on the true disease status. While past work has focused on the consequences of ignoring conditional dependence, the degree to which conditional dependence can be induced has not been systematically studied. We examine this issue in detail by introducing a hypothetical missing covariate that affects the sensitivities of two imperfect dichotomous tests. We consider four forms for this covariate, normal, uniform, dichotomous and trichotomous...
October 11, 2016: Statistics in Medicine
Garrett R Beeler Asay, Kakoli Roy, Jason E Lang, Rebecca L Payne, David H Howard
INTRODUCTION: Employers may incur costs related to absenteeism among employees who have chronic diseases or unhealthy behaviors. We examined the association between employee absenteeism and 5 conditions: 3 risk factors (smoking, physical inactivity, and obesity) and 2 chronic diseases (hypertension and diabetes). METHODS: We identified 5 chronic diseases or risk factors from 2 data sources: MarketScan Health Risk Assessment and the Medical Expenditure Panel Survey (MEPS)...
October 6, 2016: Preventing Chronic Disease
Sheng Zhong, Duo Jiang, Mary Sara McPeek
We consider the problem of genetic association testing of a binary trait in a sample that contains related individuals, where we adjust for relevant covariates and allow for missing data. We propose CERAMIC, an estimating equation approach that can be viewed as a hybrid of logistic regression and linear mixed-effects model (LMM) approaches. CERAMIC extends the recently proposed CARAT method to allow samples with related individuals and to incorporate partially missing data. In simulations, we show that CERAMIC outperforms existing LMM and generalized LMM approaches, maintaining high power and correct type 1 error across a wider range of scenarios...
October 2016: PLoS Genetics
T G Kebede, B Holtfreter, T Kocher, P Meisel, T Dietrich, R Biffar, M Dörr, H Völzke, C Pink
Current evidence indicates the effects of periodontitis on diabetes as well as mortality, for which diabetes itself represents a risk factor. However, the possible interaction of these 2 chronic conditions regarding mortality has not yet been investigated. Therefore, the purpose of this study was to evaluate whether periodontal destruction interacts with diabetes on all-cause and cardiovascular disease (CVD) mortality or if diabetes serves as a mediator in this association. The study sample comprised 3,327 participants aged 20 to 81 y from the Study of Health in Pomerania...
September 28, 2016: Journal of Dental Research
Julia K Rohr, Prudence Ive, C Robert Horsburgh, Rebecca Berhanu, Kate Shearer, Mhairi Maskew, Lawrence Long, Ian Sanne, Jean Bassett, Osman Ebrahim, Matthew P Fox
INTRODUCTION: A substantial number of patients with HIV in South Africa have failed first-line antiretroviral therapy (ART). Although individual predictors of first-line ART failure have been identified, few studies in resource-limited settings have been large enough for predictive modelling. Understanding the absolute risk of first-line failure is useful for patient monitoring and for effectively targeting limited resources for second-line ART. We developed a predictive model to identify patients at the greatest risk of virologic failure on first-line ART, and to estimate the proportion of patients needing second-line ART over five years on treatment...
2016: Journal of the International AIDS Society
Jun Tao, Han-Zhu Qian, Aaron M Kipp, Yuhua Ruan, Bryan E Shepherd, K Rivet Amico, Yiming Shao, Hongyan Lu, Sten H Vermund
OBJECTIVE: To explore the effect of depression and anxiety on adherence to antiretroviral therapy (ART) among men who have sex with men (MSM) with newly diagnosed HIV infections. DESIGN: We conducted a prospective study of Chinese MSM with newly diagnosed HIV infections. METHODS: The Hospital Anxiety and Depression Scale (HADS) was used to measure depression and anxiety at baseline, 6 and 12 months, separately. ART adherence was self-reported once every three months ("perfect" or no missing dose in the past three months vs...
September 24, 2016: AIDS
Pangaja Paramsothy, Siobán D Harlow, Bin Nan, Gail A Greendale, Nanette Santoro, Sybil L Crawford, Ellen B Gold, Ping G Tepper, John F Randolph
OBJECTIVE: The menopausal transition (MT) is a critical period associated with physiologic changes that influence women's long-term health and longevity. Information is, however, limited regarding factors that influence age at the onset of the MT and its duration (ie, time from MT onset to the final menstrual period). METHODS: We analyzed data for 1,145 women from four sites of the Study of Women's Health Across the Nation who participated in the menstrual calendar substudy, had the start of the MT identified, and had no missing covariate information...
September 26, 2016: Menopause: the Journal of the North American Menopause Society
Steven Hawken, Beth K Potter, Julian Little, Eric I Benchimol, Salah Mahmud, Robin Ducharme, Kumanan Wilson
BACKGROUND: The self-controlled case series (SCCS) is a useful design for investigating associations between outcomes and transient exposures. The SCCS design controls for all fixed covariates, but effect modification can still occur. This can be evaluated by including interaction terms in the model which, when exponentiated, can be interpreted as a relative incidence ratio (RIR): the change in relative incidence (RI) for a unit change in an effect modifier. METHODS: We conducted a scoping review to investigate the use of RIRs in published primary SCCS studies, and conducted a case-study in one of our own primary SCCS studies to illustrate the use of RIRs within an SCCS analysis to investigate subgroup effects in the context of comparing whole cell (wcp) and acellular (acp) pertussis vaccines...
2016: BMC Medical Research Methodology
Joy Simpson, Andrew D Smith, Abigail Fraser, Naveed Sattar, Mark Callaway, Robert S Lindsay, Debbie A Lawlor, Scott M Nelson
CONTEXT: Maternal adiposity in pregnancy is associated with offspring adiposity and metabolic dysfunction postnatally, including greater risk of non-alcoholic fatty liver disease (NAFLD). Recent genetic analyses suggest a causal effect of greater maternal body mass index on offspring birthweight and ponderal index but the relative roles of the environment in-utero or later in life remains unclear. OBJECTIVE: We sought to determine whether markers of infant adiposity (birthweight, umbilical cord blood leptin, adiponectin and lipids) were associated with markers of NAFLD in adolescence...
September 20, 2016: Journal of Clinical Endocrinology and Metabolism
Jonathan W Bartlett, Ruth H Keogh
Bayesian approaches for handling covariate measurement error are well established and yet arguably are still relatively little used by researchers. For some this is likely due to unfamiliarity or disagreement with the Bayesian inferential paradigm. For others a contributory factor is the inability of standard statistical packages to perform such Bayesian analyses. In this paper, we first give an overview of the Bayesian approach to handling covariate measurement error, and contrast it with regression calibration, arguably the most commonly adopted approach...
September 19, 2016: Statistical Methods in Medical Research
Soeun Kim, Thomas R Belin, Catherine A Sugar
This paper investigates multiple imputation methods for regression models with interacting continuous and binary predictors when continuous variable may be missing. Usual implementations for parametric multiple imputation assume a multivariate normal structure for the variables, which is not satisfied for a binary variable nor its interaction with a continuous variable. To accommodate interactions, missing covariates are multiply imputed from conditional distribution in a manner consistent with the joint model...
September 19, 2016: Statistical Methods in Medical Research
Scott Sibbel, Bradley J Maroni, Steven M Brunelli
Residence at higher altitude has been associated with improved anemia parameters and lower mortality rates among end-stage renal disease (ESRD) patients. However, these associations were observed prior to the 2011 shift in erythropoiesis-stimulating agent (ESA) dosing. To determine the impact of altitude on contemporary ESRD patients, a retrospective observational analysis was conducted in which patients were ascribed to one of four altitude categories as of 1 Jan 2012 and outcomes were assessed during 2012...
September 19, 2016: Journal of Nephrology
Stephen Harrap, Katrina Scurrah, Angela Lamantia, Justine Ellis
OBJECTIVE: Genes encoding key elements of the renin-angiotensin-aldosterone system (RAAS) cascade have been previously but inconsistently associated with blood pressure. Sex-dependency might be important here and functional genetic polymorphisms might exhibit epistatic effects. DESIGN AND METHOD: We assessed variation in the genes encoding renin (REN), angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin II type 1 receptor (AGTR1) and aldosterone synthase (CYP11B2)...
September 2016: Journal of Hypertension
Ernesto Roldan-Valadez, Camilo Rios, Daniel Motola-Kuba, Juan Matus-Santos, Antonio R Villa, Sergio Moreno-Jimenez
OBJECTIVE: A long-lasting concern has prevailed for the identification of predictive biomarkers for high-grade gliomas (HGGs) using MRI. However, a consensus of which imaging parameters assemble a significant survival model is still missing in the literature; we investigated the significant positive or negative contribution of several MR biomarkers in this tumour prognosis. METHODS: A retrospective cohort of supratentorial HGGs [11 glioblastoma multiforme (GBM) and 17 anaplastic astrocytomas] included 28 patients (9 females and 19 males, respectively, with a mean age of 50...
November 2016: British Journal of Radiology
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