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Missing covariates

MinJae Lee, Mohammad H Rahbar, Matthew Brown, Lianne Gensler, Michael Weisman, Laura Diekman, John D Reveille
BACKGROUND: In patient-based studies, biomarker data are often subject to left censoring due to the detection limits, or to incomplete sample or data collection. In the context of longitudinal regression analysis, inappropriate handling of these issues could lead to biased parameter estimates. We developed a specific multiple imputation (MI) strategy based on weighted censored quantile regression (CQR) that not only accounts for censoring, but also missing data at early visits when longitudinal biomarker data are modeled as a covariate...
January 11, 2018: BMC Medical Research Methodology
Paul W Bernhardt
Missing covariate values are prevalent in regression applications. While an array of methods have been developed for estimating parameters in regression models with missing covariate data for a variety of response types, minimal focus has been given to validation of the response model and influence diagnostics. Previous research has mainly focused on estimating residuals for observations with missing covariates using expected values, after which specialized techniques are needed to conduct proper inference...
January 9, 2018: Statistics in Medicine
Sanjay K Murthy, Eric I Benchimol, Jill Tinmouth, Paul D James, Robin Ducharme, Alaa Rostom, Catherine Dubé
BACKGROUND AND AIMS: Colorectal cancers (CRCs) diagnosed between 6 and 36 months after colonoscopy, termed postcolonoscopy CRCs (PCCRCs), arise primarily due to missed or inadequately treated neoplasms during colonoscopy. Quality indicators and technological advances have been introduced to colonoscopy practice that should have reduced the PCCRC rate over time. We assessed temporal trends in the population rate of PCCRC as a measure of changing colonoscopy quality. METHODS: We conducted a population-based retrospective cohort study of 50- to 74-year-old people without major risk factors for CRC who underwent complete colonoscopy in Ontario, Canada between 1996 and 2010...
January 6, 2018: Gastrointestinal Endoscopy
Oliver Lüdtke, Alexander Robitzsch, Ulrich Trautwein
The Social Relations Model (SRM) is a conceptual and analytical approach to examining dyadic behaviors and interpersonal perceptions within groups. In an SRM, the perceiver effect describes a person's tendency to perceive other group members in a certain way, whereas the target effect measures the tendency to be perceived by others in certain ways. In SRM research, it is often of interest to relate these individual SRM effects to covariates. However, the estimated individual SRM effects might not provide a very reliable measure of the true, unobserved SRM effects, resulting in distorted estimates of associations with other variables...
January 2018: Multivariate Behavioral Research
Andrew J Stasko, Alfred H Stammers, Linda B Mongero, Eric A Tesdahl, Samuel Weinstein
Utilization of intraoperative autotransfusion (IAT) during cardiac surgery with cardiopulmonary bypass (CPB) has been shown to reduce allogeneic red blood cell transfusion. Previous research has emphasized the benefits of using IAT in the intraoperative period. The present study was designed to evaluate the effects of using IAT on overall hematocrit (Hct) drift between initiation of CPB and the immediate postoperative period. We reviewed 3,225 adult cardiac procedures occurring between February 2016 and January 2017 at 84 hospitals throughout the United States...
December 2017: Journal of Extra-corporeal Technology
Nisreen Adnan Ashour, Amal Adnan Ashour, Sakeena Basha
BACKGROUND: Dental caries and obesity are multifactorial diseases with diet being a common contributory factor. OBJECTIVE: The main purpose of the present study was to investigate the association between dental caries and obesity among special care female school children in Makkah City, Saudi Arabia. DESIGN: Analytical cross-sectional study. SETTING: Special schools in Makkah City. STUDY POPULATION AND METHODS: Schools were chosen by lottery and female children were ran...
December 31, 2017: Annals of Saudi Medicine
Eira Roos, Tea Lallukka, Eero Lahelma, Ossi Rahkonen
BACKGROUND: Both smoking and obesity are separately associated with sickness absence. Unhealthy lifestyle habits and health conditions may occur concurrently yet studies focusing on their joint association are few. This study examined the joint associations of smoking and obesity with sickness absence (SA). METHODS: A mail survey among employees of the City of Helsinki, Finland, during 2000-2002 included data on obesity, smoking and covariates (N = 8960, response rate 67%, 80% women)...
December 28, 2017: BMC Public Health
Chia-Shi Wang, Jennifer Gander, Rachel E Patzer, Larry A Greenbaum
BACKGROUND: Pediatric patients with focal segmental glomerulosclerosis (FSGS) have high rates of disease recurrence and allograft failure after kidney transplantation, but there are few data for long-term survival posttransplantation. STUDY DESIGN: Retrospective cohort study. SETTING & PARTICIPANTS: 12,303 pediatric patients (aged <18 years), including 1,408 (11%) patients with FSGS, who received a first kidney transplant in 1990 through 2009 and were followed up through June 2015 were identified from the US Renal Data System database...
December 22, 2017: American Journal of Kidney Diseases: the Official Journal of the National Kidney Foundation
Hua Weng, Randall Bateman, John C Morris, Chengjie Xiong
We studied the validity of longitudinal statistical inferences of clinical trials using minimization, a dynamic randomization algorithm designed to minimize treatment imbalance for prognostic factors. Repeated measures analysis of covariance and the random intercept and slope models, were used to simulate longitudinal clinical trials randomized by minimization or simple randomization. The simulations represented a wide range of analyses in real-world trials, including missing data caused by dropouts, unequal allocation of treatment arms, and efficacy analyses on either the original outcome or its change from baseline...
2017: Biostatistics & Epidemiology
Abbie Barry, Nathan Ford, Ziad El-Khatib
OBJECTIVES: To assess adherence outcomes to antiretroviral therapy (ART) of recipients ≥50 years in Soweto, South Africa. METHODS: This was a secondary data analysis for a cross-sectional study at two HIV clinics in Soweto. Data on ART adherence and covariates were gathered through structured interviews with HIV 878 persons living with HIV (PLHIV) receiving ART. Logistic regression analysis was used to assess associations. RESULTS: PLHIV ≥50 years (n=103) were more likely to miss clinic visits during the last six months than PLHIV aged 25 - 49 years (OR 2...
December 15, 2017: Tropical Medicine & International Health: TM & IH
Rianne Jacobs, Emmanuel Lesaffre, Peter Fm Teunis, Michael Höhle, Jan van de Kassteele
Early identification of contaminated food products is crucial in reducing health burdens of food-borne disease outbreaks. Analytic case-control studies are primarily used in this identification stage by comparing exposures in cases and controls using logistic regression. Standard epidemiological analysis practice is not formally defined and the combination of currently applied methods is subject to issues such as response misclassification, missing values, multiple testing problems and small sample estimation problems resulting in biased and possibly misleading results...
January 1, 2017: Statistical Methods in Medical Research
Ariel Linden, Paul R Yarnold
RATIONALE, AIMS AND OBJECTIVES: A common approach to assessing treatment effects in nonrandomized studies with time-to-event outcomes is to estimate propensity scores and compute weights using logistic regression, test for covariate balance, and then estimate treatment effects using Cox regression. A machine-learning alternative-classification tree analysis (CTA)-used to generate propensity scores and to estimate treatment effects in time-to-event data may identify complex relationships between covariates not found using conventional regression-based approaches...
December 12, 2017: Journal of Evaluation in Clinical Practice
Christian Plewnia, Bettina Brendel, Tobias Schwippel, Peter Martus, Joachim Cordes, Alkomiet Hasan, Andreas J Fallgatter
Auditory verbal hallucinations (AH) are core symptoms of schizophrenia. They are often severely distressing and refractory to therapy. Their perception is associated with increased activity in temporoparietal areas of the brain. Repetitive transcranial magnetic stimulation (rTMS) can reduce focal brain hyperactivity and has been shown to ameliorate AH. However, controlled multicenter clinical trials are still missing, effect sizes are moderate, and the treatment with rTMS is time consuming. Continuous theta burst stimulation (cTBS) is a quicker and potentially more effective technique to reduce cortical hyperactivity...
December 9, 2017: European Archives of Psychiatry and Clinical Neuroscience
Cheuk Fan Shum, Clinton D Bahler, Chandru P Sundaram
INTRODUCTION: The impact of positive surgical margins (PSM) in partial nephrectomy (PN) has been a controversy. Previous studies on the relationship between PSM and overall survival (OS) were either underpowered or had highly dissimilar groups. We used the National Cancer Database with propensity score matching to determine the association between PSM and OS after PN. MATERIALS AND METHODS: We identified patients with T1/T2 N0M0 renal cancer treated with PN between 2004 and 2009, and divided them into 2 groups based on their margin status...
December 6, 2017: Urologic Oncology
Caleb Alan Cooper, Cheuk Fan Shum, Clinton D Bahler, Chandru P Sundaram
OBJECTIVE: Intraoperative mannitol is routinely administered for renoprotection in partial nephrectomy (PN). However, there is a paucity of evidence supporting mannitol's renoprotective effect. We performed a retrospective study of mannitol's efficacy in PN. METHODS: Using an institutional database, patients undergoing PN from 2006-2016 were retrospectively identified and divided into two groups based on mannitol use. Cases with missing serum creatinine measurements were excluded...
December 7, 2017: Journal of Endourology
Rafael V Picon, Lúcia Fendt, Karine Amaral, Paulo D Picon
Aim: Peginterferon plus ribavirin (peg-IFN/RBV) is still the standard of care for treatment of hepatitis C virus (HCV) in many countries. Given the high toxicity of this regimen, our study aimed to develop a prediction tool that can identify which patients are unlikely to benefit from peg-IFN/RBV and could thus postpone treatment in favor of new-generation direct-acting antivirals. Materials and methods: Binary regression was performed using demographic, clinical, and laboratory covariates and sustained virological response (SVR) outcomes from a prospective cohort of individuals referred for therapy from 2003 to 2008 in a public HCV treatment center in Rio Grande do Sul, Brazil...
January 2017: Euroasian Journal of Hepato-Gastroenterology
Caroline Fenlon, Luke O'Grady, Stephen Butler, Michael L Doherty, John Dunnion
Background: Herd fertility in pasture-based dairy farms is a key driver of farm economics. Models for predicting nulliparous reproductive outcomes are rare, but age, genetics, weight, and BCS have been identified as factors influencing heifer conception. The aim of this study was to create a simulation model of heifer conception to service with thorough evaluation. Methods: Artificial Insemination service records from two research herds and ten commercial herds were provided to build and evaluate the models...
2017: Irish Veterinary Journal
Hyang Kim, Greg Cable
Assessing treatment effectiveness in longitudinal data can be complex when treatments are not randomly assigned and patients are allowed to switch treatment to other or no treatment, often in a manner that is driven by changes in one or more variables associated with patient or clinical characteristics. There can be confounding of the treatment effect from a time-varying variable, i.e., one which is affected by previous exposure and can in turn also influence subsequent treatment changes. Precision medicine relies on validated biomarkers to better classify patients by their probable response to treatment...
December 4, 2017: Journal of Biopharmaceutical Statistics
Chengjie Xiong, Jingqin Luo, Ling Chen, Feng Gao, Jingxia Liu, Guoqiao Wang, Randall Bateman, John C Morris
Many medical diagnostic studies involve three ordinal diagnostic populations in which the diagnostic accuracy can be summarized by the volume or partial volume under the receiver operating characteristic surface for a diagnostic marker. When the diagnostic populations are clustered, e.g. by families, we propose to model the diagnostic marker by a general linear mixed model that takes into account of the correlation on the diagnostic marker from members of the same clusters. This model then facilitates the maximum likelihood estimation and statistical inferences of the diagnostic accuracy for the diagnostic marker...
January 1, 2017: Statistical Methods in Medical Research
Kalyan Das, Subrata Rana, Surupa Roy
In clinical trials, patient's disease severity is usually assessed on a Likert-type scale. Patients, however, may miss one or more follow-up visits (non-monotone missing). The statistical analysis of non-Gaussian longitudinal data with non-monotone missingness is difficult to handle, particularly when both response and time-dependent covariates are subject to such missingness. Even when the number of patients with intermittent missing data is small, ignoring those patients from analysis seems to be unsatisfactory...
November 27, 2017: Journal of Biopharmaceutical Statistics
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