Medicine and Health Sciences Commons^™

Application Of Two Machine Learning Algorithms To Genetic Association Studies In The Presence Of Covariates, Bareng As Nonyane, Andrea S. Foulkes

Andrea S Foulkes

Background - Population-based investigations aimed at uncovering genotype-trait associations often involve high-dimensional genetic polymorphism data as well as information on multiple environmental and clinical parameters. Machine learning (ML) algorithms offer a straightforward analytic approach for selecting subsets of these inputs that are most predictive of a pre-defined trait. The performance of these algorithms, however, in the presence of covariates is not well characterized. Methods and Results - In this manuscript, we investigate two approaches: Random Forests (RFs) and Multivariate Adaptive Regression Splines (MARS). Through multiple simulation studies, the performance under several underlying models is evaluated. An application to a cohort …

Association Between Dietary Glycemic Index, Glycemic Load, And High-Sensitivity C-Reactive Protein, Jennifer A. Griffith, Yusheng Ma, Lisa Chasan-Taber, Barbara C. Olendzki, David E. Chiriboga, Edward J. Stanek, Philip A. Merriam, Ira S. Ockene

Edward J. Stanek

OBJECTIVE:

This study examined the relation between quality of dietary carbohydrate intake, as measured by glycemic index (GI) and glycemic load (GL), and serum high-sensitivity C-reactive protein (hs-CRP) levels. METHODS:

During a 1-y observational study, data were collected at baseline and at each quarter thereafter. GI and GL were calculated from multiple 24-h dietary recalls (24HRs), 3 randomly selected 24HRs at every quarter, with up to 15 24HRs per participant. The hs-CRP was measured in blood samples collected at baseline and each of the four quarterly measurement points. Multivariable linear mixed models were used to examine the cross-sectional and longitudinal …

Effect Of Diet And Exercise On Body Composition, Energy Intake And Leptin Levels In Overweight Women And Men, Stella L. Volpe, Hati Kobusingye, Smita Bailfur, Edward J. Stanek

Edward J. Stanek

OBJECTIVE: To investigate the effect of diet alone (D), exercise alone (E), and a combination of diet and exercise (DE) on body weight, body composition, energy intake, blood pressure, serum lipid and leptin levels, and fitness levels in mildly obese sedentary women and men. DESIGN: The three interventions were compared in a randomized longitudinal study design. The exercise programs were supervised for six months, after which participants in E and DE were provided with exercise equipment to take home. SUBJECTS: 90 adult overweight women and men (age: 44.2 +/- 7.2 years; BMI = 30.5 +/- 2.7 kg/m(2)). MEASUREMENTS: Body weight, …

Should Adjustment For Covariates Be Used In Prevalence Estimations?, Wenjun Li, Edward J. Stanek, Elizabeth R. Bertone-Johnson

Edward J. Stanek

Background

Adjustment for covariates (also called auxiliary variables in survey sampling literature) is commonly applied in health surveys to reduce the variances of the prevalence estimators. In theory, adjusted prevalence estimators are more accurate when variance components are known. In practice, variance components needed to achieve the adjustment are unknown and their sample estimators are used instead. The uncertainty introduced by estimating variance components may overshadow the reduction in the variance of the prevalence estimators due to adjustment. We present empirical guidelines indicating when adjusted prevalence estimators should be considered, using gender adjusted and unadjusted smoking prevalence as an illustration. …

Changes In Muscle And Joint Coordination In Learning To Direct Forces, Christopher Hasson, Graham Caldwell, Richard Van Emmerik

Richard E.A. van Emmerik

While it has been suggested that biarticular muscles have a specialized role in directing external reaction forces, it is unclear how humans learn to coordinate mono- and bi-articular muscles to perform force-directing tasks. Subjects were asked to direct pedal forces in a specified target direction during one-legged cycling. We expected that with practice, performance improvement would be associated with specific changes in joint torque patterns and mono- and bi-articular muscular coordination. Nine male subjects practiced pedaling an ergometer with only their left leg, and were instructed to always direct their applied pedal force perpendicular to the crank arm (target direction) …

Monitoring Microbial Populations On Wide-Body Commercial Passenger Aircraft, Taylor L. Mckernan, K M. Wallingford, M J. Hein, H A. Burge, Christine A. Rogers, R Herrick

Christine A. Rogers

Although exposure to bacteria has been assessed in cabin air previously, minimal numbers of samples have been collected in-flight. The purpose of this research was to comprehensively characterize bacterial concentrations in the aircraft cabin. Twelve randomly selected flights were sampled on Boeing-767 aircraft, each with a flight duration between 4.5 and 6.5 h. N-6 impactors were used to collect sequential, triplicate air samples in the front and rear of coach class during six sampling intervals throughout each flight: boarding, mid-climb, early cruise, mid-cruise, late cruise and deplaning. Comparison air samples were also collected inside and outside the airport terminals at …

A Likelihood-Based Approach To Mixed Modeling With Ambiguity In Cluster Identifiers, Andrea S. Foulkes, Recai Yucel, Xiaohong Li

Andrea S Foulkes

This manuscript describes a novel, linear mixed-effects model–fitting technique for the setting in which correlated data indicators are not completely observed. Mixed modeling is a useful analytical tool for characterizing genotype–phenotype associations among multiple potentially informative genetic loci. This approach involves grouping individuals into genetic clusters, where individuals in the same cluster have similar or identical multilocus genotypes. In haplotype-based investigations of unrelated individuals, corresponding cluster assignments are unobservable since the alignment of alleles within chromosomal copies is not generally observed. We derive an expectation conditional maximization approach to estimation in the mixed modeling setting, where cluster assignments are ambiguous. …