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Missing covariates

Holly J Bowen, Cheryl L Grady, Julia Spaniol
Affective processing is one domain that remains relatively intact in healthy aging. Investigations into the neural responses associated with reward anticipation have revealed that older and younger adults recruit the same midbrain reward regions, but other evidence suggests this recruitment may differ depending on the valence (gain, loss) of the incentive cue. The goal of the current study was to examine functional covariance during gain and loss feedback in younger and healthy older adults. A group of 15 older adults (mean age = 68...
May 21, 2018: Neuropsychology, Development, and Cognition. Section B, Aging, Neuropsychology and Cognition
Soohyun Ahn, Johan Lim, Myunghee Cho Paik, Ralph L Sacco, Mitchell S Elkind
In cohort studies the outcome is often time to a particular event, and subjects are followed at regular intervals. Periodic visits may also monitor a secondary irreversible event influencing the event of primary interest, and a significant proportion of subjects develop the secondary event over the period of follow-up. The status of the secondary event serves as a time-varying covariate, but is recorded only at the times of the scheduled visits, generating incomplete time-varying covariates. While information on a typical time-varying covariate is missing for entire follow-up period except the visiting times, the status of the secondary event are unavailable only between visits where the status has changed, thus interval-censored...
May 18, 2018: Biometrical Journal. Biometrische Zeitschrift
T Kühl, S Behrens, A Jung, N Obi, K Thöne, M E Schmidt, H Becher, J Chang-Claude
BACKGROUND: Studies to date have reported several associations between single nucleotide polymorphisms (SNPs) and cancer related fatigue (CRF), but have been limited by small sample sizes, missing adjustment for relevant covariates or multiple testing, as well as varying CRF definitions, i.e. time and method of assessment. This study aimed to validate previously reported associations using the largest independent breast cancer sample to date and to evaluate further functional cytokine variants in relation to total CRF and all relevant CRF subdomains (physical, cognitive, and affective CRF)...
May 12, 2018: Brain, Behavior, and Immunity
Roseanne C Schuster, Seung Yong Han, Alexandra A Brewis, Amber Wutich
Obesity is socially stigmatized in the U.S., especially for women. Significant research has focused on the role that the social and built environments of neighborhoods play in shaping obesity. However, the role of obesity in shaping neighborhood social structure has been largely overlooked. We test the hypothesis that large body size inhibits an individual's engagement in his or her neighborhood. Our study objectives are to assess if (1) body size (body mass index) interacts with gender to predict engagement in one's neighborhood (neighborhood engagement) and (2) if bonding social capital interacts with gender to predict neighborhood engagement independent of body size...
June 2018: Preventive Medicine Reports
Andreas A Ioannides
Neurofeedback has been around for half a century, but despite some promising results it is not yet widely appreciated. Recently, some of the concerns about neurofeedback have been addressed with functional magnetic resonance imaging and magnetoencephalography adding their contributions to the long history of neurofeedback with electroencephalography. Attempts to address other concerns related to methodological issues with new experiments and meta-analysis of earlier studies, have opened up new questions about its efficacy...
2018: Frontiers in Human Neuroscience
Habtamu K Benecha, John S Preisser, Kimon Divaris, Amy H Herring, Kalyan Das
Unlike zero-inflated Poisson regression, marginalized zero-inflated Poisson (MZIP) models for counts with excess zeros provide estimates with direct interpretations for the overall effects of covariates on the marginal mean. In the presence of missing covariates, MZIP and many other count data models are ordinarily fitted using complete case analysis methods due to lack of appropriate statistical methods and software. This article presents an estimation method for MZIP models with missing covariates. The method, which is applicable to other missing data problems, is illustrated and compared with complete case analysis by using simulations and dental data on the caries preventive effects of a school-based fluoride mouthrinse program...
May 11, 2018: Biometrical Journal. Biometrische Zeitschrift
Marco Aurelio Peres, Pingzhou Liu, Flavio Fernando Demarco, Alexandre Emidio Ribeiro Silva, Fernando Cesar Wehrmeister, Ana Maria Menezes, Karen Glazer Peres
We aimed to analyze the effects of family income trajectories on the increase in dental caries from childhood to young adulthood. Data from the 1993 Pelotas (Brazil) birth cohort study, in which dental caries was measured at ages 6, 12, and 18 years, were analyzed. Family income of 302 participants was assessed at birth, and at 4, 11, 15, and 18 years of age. Mother's education, toothbrushing frequency, dental visiting, dental caries in primary dentition, and birth weight were covariates. A latent class growth analysis was conducted to characterize trajectories of time-varying variables...
2018: Brazilian Oral Research
Chiu-Hsieh Hsu, Mandi Yu
We consider the situation of estimating Cox regression in which some covariates are subject to missing, and there exists additional information (including observed event time, censoring indicator and fully observed covariates) which may be predictive of the missing covariates. We propose to use two working regression models: one for predicting the missing covariates and the other for predicting the missing probabilities. For each missing covariate observation, these two working models are used to define a nearest neighbor imputing set...
January 1, 2018: Statistical Methods in Medical Research
Hye-Young Jung, Sangseob Leem, Taesung Park
BACKGROUND: Gene-gene interactions (GGIs) are a known cause of missing heritability. Multifactor dimensionality reduction (MDR) is one of most commonly used methods for GGI detection. The generalized multifactor dimensionality reduction (GMDR) method is an extension of MDR method that is applicable to various types of traits, and allows covariate adjustments. Our previous Fuzzy MDR (FMDR) is another extension for overcoming simple binary classification. FMDR uses continuous member-ship values instead of binary membership values 0 and 1, improving power for detecting causal SNPs and more intuitive interpretations in real data analysis...
April 20, 2018: BMC Medical Genomics
Sean DuBois, Ankur R Desai, Aditya Singh, Shawn P Serbin, Michael L Goulden, Dennis D Baldocchi, Siyan Ma, Walter C Oechel, Sonia Wharton, Eric L Kruger, Philip A Townsend
A central challenge to understanding how climate anomalies, such as drought and heatwaves, impact the terrestrial carbon cycle, is quantification and scaling of spatial and temporal variation in ecosystem gross primary productivity (GPP). Existing empirical and model-based satellite broadband spectra-based products have been shown to miss critical variation in GPP. Here, we evaluate the potential of high spectral resolution (10 nm) shortwave (400-2500 nm) imagery to better detect spatial and temporal variations in GPP across a range of ecosystems, including forests, grassland-savannas, wetlands, and shrublands in a water-stressed region...
April 25, 2018: Ecological Applications: a Publication of the Ecological Society of America
Amir Almasi-Hashiani, Saharnaz Nedjat, Mohammad Ali Mansournia
The goal of many observational studies is to estimate the causal effect of an exposure on an outcome after adjustment for confounders, but there are still some serious errors in adjusting confounders in clinical journals. Standard regression modeling (e.g., ordinary logistic regression) fails to estimate the average effect of exposure in total population in the presence of interaction between exposure and covariates, and also cannot adjust for time-varying confounding appropriately. Moreover, stepwise algorithms of the selection of confounders based on P values may miss important confounders and lead to bias in effect estimates...
April 1, 2018: Archives of Iranian Medicine
Duduzile Ndwandwe, Olalekan A Uthman, Abdu Adamu, Evanson Z Sambala, Alison B Wiyeh, Tawa Olukade, Ghose Bishwajit, Sanni Yaya, Jean-Marie Okwo-Bele, Charles S Wiysonge
Understanding the gaps in missed opportunities for vaccination (MOV) between poor and non-poor in sub-Saharan Africa (SSA) would enable an understanding of factors associated with interventions for improving immunisation coverage to achieving universal childhood immunisation. We aimed to conduct a multicountry analyses to decompose the gap in MOV between poor and non-poor in SSA. We used cross-sectional data from 35 Demographic and Health Surveys in SSA conducted between 2007 and 2016. Descriptive statistics used to understand the gap in MOV between the urban poor and non-poor, and across the selected covariates...
April 24, 2018: Human Vaccines & Immunotherapeutics
Jesse T Young, Ed Heffernan, Rohan Borschmann, James R P Ogloff, Matthew J Spittal, Fiona G Kouyoumdjian, David B Preen, Amanda Butler, Lisa Brophy, Julia Crilly, Stuart A Kinner
BACKGROUND: People with mental illness and substance use disorder are over-represented in prisons. Injury-related mortality is elevated in people released from prison, and both mental illness and substance use disorder are risk factors for injury. Effective care coordination during the transition between criminal justice and community service providers improves health outcomes for people released from prison. However, the health outcomes and support needs of people with dual diagnosis (co-occurring mental illness and substance use disorder) released from prison are poorly understood...
April 17, 2018: Lancet. Public Health
Wei-Yin Loh, Michael Man, Shuaicheng Wang
Identification of subgroups with differential treatment effects in randomized trials is attracting much attention. Many methods use regression tree algorithms. This article addresses 2 important questions arising from the subgroups: how to ensure that treatment effects in subgroups are not confounded with effects of prognostic variables and how to determine the statistical significance of treatment effects in the subgroups. We address the first question by selectively including linear prognostic effects in the subgroups in a regression tree model...
April 19, 2018: Statistics in Medicine
Tracey E Wilson, Emma Sophia Kay, Bulent Turan, Mallory O Johnson, Mirjam-Colette Kempf, Janet M Turan, Mardge H Cohen, Adaora A Adimora, Margaret Pereyra, Elizabeth T Golub, Lakshmi Goparaju, Lynn Murchison, Gina M Wingood, Lisa R Metsch
INTRODUCTION: This study assessed longitudinal relationships between patient healthcare empowerment, engagement in care, and viral control in the Women's Interagency HIV Study, a prospective cohort study of U.S. women living with HIV. METHODS: From April 2014 to March 2016, four consecutive 6-month visits were analyzed among 973 women to assess the impact of Time 1 healthcare empowerment variables (Tolerance for Uncertainty and the state of Informed Collaboration Committed Engagement) on Time 2 reports of ≥95% HIV medication adherence and not missing an HIV primary care appointment since last visit; and on HIV RNA viral control across Times 3 and 4, controlling for illicit drug use, heavy drinking, depression symptoms, age, and income...
April 12, 2018: American Journal of Preventive Medicine
Xiaowei Wu, Mary Sara McPeek
In complex-trait mapping, when each subject has multiple measurements of a quantitative trait over time, power for detecting genetic association can be gained by the inclusion of all measurements and not just single time points or averages in the analysis. To increase power and control type 1 error, one should account for dependence among observations for a single individual as well as dependence between observations of related individuals if they are present in the sample. We propose L-GATOR, a retrospective, mixed-effects method for association mapping of longitudinally measured traits in samples with related individuals...
April 5, 2018: American Journal of Human Genetics
Lily Siok Hoon Lim, Brian M Feldman, Lisa M Lix
Longitudinal cohort designs (with three or more measurement occasions) are invaluable to investigate between- and within-individual variation in outcomes. However, traditional longitudinal designs require a lengthy implementation and data collection period and impose a substantial burden on participants and investigators. We discuss alternative longitudinal designs, including planned missing data designs and retrospective cohort studies with secondary data, which require a shorter period for data accrual and reduce participant burden while maintaining statistical power...
May 2018: Rheumatic Diseases Clinics of North America
Dai Feng, Richard Baumgartner, Vladimir Svetnik
The concordance correlation coefficient (CCC) is a widely used scaled index in the study of agreement. In this article, we propose estimating the CCC by a unified Bayesian framework that can (1) accommodate symmetric or asymmetric and light- or heavy-tailed data; (2) select model from several candidates; and (3) address other issues frequently encountered in practice such as confounding covariates and missing data. The performance of the proposal was studied and demonstrated using simulated as well as real-life biomarker data from a clinical study of an insomnia drug...
April 5, 2018: International Journal of Biostatistics
Tamara Nsubuga-Nyombi, Simon Sensalire, Esther Karamagi, Judith Aloyo, John Byabagambi, Mirwais Rahimzai, Linda Kisaakye Nabitaka, Jacqueline Calnan
BACKGROUND: As part of efforts to improve the prevention of mother-to-child transmission in Northern Uganda, we explored reasons for poor viral suppression among 122 pregnant and lactating women who were in care, received viral load tests, but had not achieved viral suppression and had more than 1000 copies/mL. Understanding the patient factors associated with low viral suppression was of interest to the Ministry of Health to guide the development of tools and interventions to achieve viral suppression for pregnant and lactating women newly initiating on ART as well as those on ART with unsuppressed viral load...
March 31, 2018: AIDS Research and Therapy
Benjamin D Stocker, Jakob Zscheischler, Trevor F Keenan, I Colin Prentice, Josep Peñuelas, Sonia I Seneviratne
Terrestrial primary productivity and carbon cycle impacts of droughts are commonly quantified using vapour pressure deficit (VPD) data and remotely sensed greenness, without accounting for soil moisture. However, soil moisture limitation is known to strongly affect plant physiology. Here, we investigate light use efficiency, the ratio of gross primary productivity (GPP) to absorbed light. We derive its fractional reduction due to soil moisture (fLUE), separated from VPD and greenness changes, using artificial neural networks trained on eddy covariance data, multiple soil moisture datasets and remotely sensed greenness...
March 31, 2018: New Phytologist
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