Papers by Timothy Beasley
Journal of Immigrant and Minority Health, Apr 25, 2020
The present study assessed how the adaptation to American culture by United States (U.S.)-born an... more The present study assessed how the adaptation to American culture by United States (U.S.)-born and foreign-born Hispanics living in the U.S. may influence stress-related physiological aspects that may impair health. Methods: Data on 8,360 Hispanics living in the U.S. categorized as U.S.-born (n=3,347) and foreign-born (n=5,013) from NHANES 1999-2010 (ages 18-85) were used. Stress-related physiological impact was measured by the allostatic load index (ALoad). Adaptation to American culture was evaluated through three acculturation-related measures. The average age was 39.39 years in a sample where 51% were males. ALoad was classified as no load (15.41%), low load (55.33%), and high load (29.24%). The U.S.-born Hispanics showed higher ALoad compared to foreign-born Hispanics (p<0.001). Among foreign born Hispanics, length of residence (LOR) and age of arrival in the U.S. (AOA) were associated with higher ALoad scores (p<0.05), and in U.S.-born Hispanics, age and sex were positively associated and education was negatively associated with ALoad scores (p<0.05).
Obesity, 2011
Aerobic fitness and adiposity are each independently associated with health outcomes among childr... more Aerobic fitness and adiposity are each independently associated with health outcomes among children, although the relationship between these two variables is unclear. Our objectives were to evaluate 1) the association of adiposity with aerobic fitness using objectively measured levels of percent body fat, compared to body mass index (BMI) as a percentile proxy for adiposity while controlling for genetic admixture, and 2) the congruence of BMI categories with high and low body fat categories of objectively measured percent body fat. Participants were 232 African-American, European-American, and Hispanic-American children aged 7-12 years (Tanner stage ≤ 3). Aerobic fitness was measured via a submaximal indirect calorimetry treadmill test (VO 2-170 ), and physical activity levels with accelerometry. Genetic admixture estimates were obtained using 140 genetic ancestry informative markers to estimate European, African, and Amerindian admixture. Fat mass was determined using dual-energy x-ray absorptiometry. Children were classified into a low body fat group (< 25% in males, < 30% in females) or a high body fat group based on their percent body fat; children were also categorized according to BMI percentile. Children in the low body fat group had significantly higher aerobic fitness (P < 0.05) regardless of BMI percentile classification. Higher African genetic admixture was associated with lower aerobic fitness (P < 0.05), while physical activity was positively associated with fitness (P < 0.01). In conclusion, aerobic fitness levels differ by percent body fat and genetic admixture irrespective of BMI classification, and such differences should be taken into account when evaluating outcomes of health interventions.
PLOS Genetics, Aug 25, 2006
Individual genetic admixture estimates, determined both across the genome and at specific genomic... more Individual genetic admixture estimates, determined both across the genome and at specific genomic regions, have been proposed for use in identifying specific genomic regions harboring loci influencing phenotypes in regional admixture mapping (RAM). Estimates of individual ancestry can be used in structured association tests (SAT) to reduce confounding induced by various forms of population substructure. Although presented as two distinct approaches, we provide a conceptual framework in which both RAM and SAT are special cases of a more general linear model. We clarify which variables are sufficient to condition upon in order to prevent spurious associations and also provide a simple closed form ''semiparametric'' method of evaluating the reliability of individual admixture estimates. An estimate of the reliability of individual admixture estimates is required to make an inherent errors-in-variables problem tractable. Casting RAM and SAT methods as a general linear model offers enormous flexibility enabling application to a rich set of phenotypes, populations, covariates, and situations, including interaction terms and multilocus models. This approach should allow far wider use of RAM and SAT, often using standard software, in addressing admixture as either a confounder of association studies or a tool for finding loci influencing complex phenotypes in species as diverse as plants, humans, and nonhuman animals.
General Linear Model Journal, 2019
By substituting the matrices necessary to compute Mean Corrected Sums of Squares and Cross-Produc... more By substituting the matrices necessary to compute Mean Corrected Sums of Squares and Cross-Products into the Pearson correlation scalar formula and utilizing the idempotent properties of partitioned matrices, it is demonstrated that computationally the Multiple R IS the square root of the Model R 2. hile preparing for my preliminary examinations to qualify as a doctoral candidate, I worked through many practice questions. One such question was: "Why is the Multiple Correlation Coefficient, R, always positive?" I was told by fellow students that: "The Multiple Correlation Coefficient is the square root of the Multiple Coefficient of Determination, R = √ 2 ." was not a "good enough" answer. Something more elaborate was needed. A more verbose response would be as follows. The Multiple Correlation Coefficient can be defined as the Pearson Correlation between the outcome variable, y, and the predicted values, �, from regressing y onto a set of x variables. The predicted values, �, determined from the Ordinary Least Squares (OLS) regression solution are calculated as: � = b0 + b1x1 + … + bkxk. The OLS regression solution determines regression coefficients and predicted values that minimize the Sum of Squared Residuals (Σ(y-�) 2), thus yielding the best fit of � for y. Therefore, the OLS regression solutions will project � into the same space as y. For example, suppose a simple linear regression with one regressor, x1. If x1 is negatively (inversely) correlated with y, the regression slope for x1 (b1) will be negative. This can be seen in the scalar formula for the slope in simple regression: b1 = ry1(Sy/S1); where ry1 is the Pearson correlation between y and x1; Sy and S1 are the standard deviations of y and x1, respectively. When the predicted values are calculated, the negative slope reverses x1 and projects � into the same direction as y. In contrast to the negative correlation between y and x1, the Pearson Correlation between y, and the predicted values, �, Ry �, will be positive. This property generalizes to multiple regression, where x variables that have negative partial relationships with y, will have negative partial regression coefficients that will project � into the same space (direction) as y. Thus, the Multiple Correlation Coefficient is always greater than or equal to zero (Ry � ≥ 0). As wordy and potentially convincing as this may seem, a more mathematical approach using the matrix formulation of multiple regression is used to demonstrate why the Multiple Correlation Coefficient is always positive (Ry � ≥ 0) and IS equal to the square root of R 2 computationally. Table 1 reports the data for a basic k = 4 x variable regression problem with a small sample size of N=10. This sample size to variables ratio is not recommended in applied statistical practice, but rather these data are intended to provide concrete illustrations. In the notation that follows, lowercase bold font denotes vectors or variables (e.g., x1); upper-case bold font denotes matrices (e.g., X1; H0), and italics are used for other statistical terms (ry1). Matrix Approach to Pearson Correlation The Pearson Correlation can be defined in many ways. For the following illustrations, the Pearson Correlation will be calculated as the Mean Corrected Cross-Product (numerator) in ratio to the square root of Mean Corrected Sums of Squares for each variable (denominator). As an example, the Pearson Correlation between y and x1 yields the following scalar formula:
Clinical and Applied Thrombosis/Hemostasis, 2018
We conducted a prospective serial laboratory cohort study to assess the correlation of factor VII... more We conducted a prospective serial laboratory cohort study to assess the correlation of factor VIII (FVIII) levels in response to thrombolysis in patients with large vessel occlusion (LVO) and acute ischemic stroke (AIS). Patients with AIS with anterior circulation LVO were eligible for enrollment if treated within 4.5 hours from last seen normal with intravenous tissue plasminogen activator (tPA). Patients (n = 29) had a mean age of 71 years and median National Institute of Health Stroke Scale of 14. Baseline pre-tPA FVIII was not significantly correlated with clot burden score (−0.147, P = .447) or vessel recanalization (−0.133, P = .499). Median FVIII decreased significantly from baseline to 6 hours post-tPA (282% to 161%, P = .002), but delta in FVIII level did not correlate with vessel recanalization (0.013, P = .948). There was no difference between median FVIII level at baseline and 90 days post-AIS. FVIII level decreased significantly after tPA, but baseline FVIII level and e...
Journal of the American Geriatrics Society, 2019
Journal of stroke and cerebrovascular diseases : the official journal of National Stroke Association, 2015
A1 segment is the proximal portion of anterior cerebral artery. Absence of the A1 segment can com... more A1 segment is the proximal portion of anterior cerebral artery. Absence of the A1 segment can compromise anterior cerebral collateral blood flow. Few studies have examined the association of an absent A1 segment and ischemic stroke outcome. We sought to determine the association between A1 absence and affected vessel territory, stroke volume, and outcomes among patients with acute ischemic stroke (AIS). A retrospective review of prospectively identified patients with AIS from July 2008 to March 2013 was performed. Patients without intracranial vascular imaging were excluded. We compared patients with absent A1 to patients with bilateral A1 segments in terms of demographics, stroke severity (as measured by National Institute of Health Stroke Scale [NIHSS]), vascular distribution, and in-hospital mortality using the chi-square test and logistic regression. Of the 1146 patients with AIS and intracranial vascular imaging, 5.9% patients (n = 68) had absent A1. Compared with other AIS pat...
Journal of Stroke and Cerebrovascular Diseases, 2014
BACKGROUND: Systemic inflammatory response syndrome (SIRS) is an inflammatory process associated ... more BACKGROUND: Systemic inflammatory response syndrome (SIRS) is an inflammatory process associated with poor outcomes in acute ischemic stroke (AIS) patients. However, no study to date has investigated predictors of SIRS in AIS patients treated with intravenous (IV) tissue plasminogen activator (tPA).
Journal of Stroke and Cerebrovascular Diseases, 2013
Background-To date, few studies have assessed the influence of infections present on admission (P... more Background-To date, few studies have assessed the influence of infections present on admission (POA) compared with hospital-acquired infections (HAIs) on neurologic deterioration (ND) and other outcome measures in acute ischemic stroke (AIS). Methods-Patients admitted with AIS to our stroke center (July 2010 to December 2010) were retrospectively assessed. The following infections were assessed: urinary tract infection, pneumonia, and bacteremia. Additional chart review was performed to determine whether the infection was POA or HAI. We assessed the relationship between infections in ischemic stroke
Cell metabolism, Jun 14, 2016
Calorie restriction (CR) is the most robust non-genetic intervention to delay aging. However, the... more Calorie restriction (CR) is the most robust non-genetic intervention to delay aging. However, there are a number of emerging experimental variables that alter CR responses. We investigated the role of sex, strain, and level of CR on health and survival in mice. CR did not always correlate with lifespan extension, although it consistently improved health across strains and sexes. Transcriptional and metabolomics changes driven by CR in liver indicated anaplerotic filling of the Krebs cycle together with fatty acid fueling of mitochondria. CR prevented age-associated decline in the liver proteostasis network while increasing mitochondrial number, preserving mitochondrial ultrastructure and function with age. Abrogation of mitochondrial function negated life-prolonging effects of CR in yeast and worms. Our data illustrate the complexity of CR in the context of aging, with a clear separation of outcomes related to health and survival, highlighting complexities of translation of CR into ...
C. L. Olson (1976, 1979) suggests the Pillai-Bartlett trace (V) as an omnibus multivariate analys... more C. L. Olson (1976, 1979) suggests the Pillai-Bartlett trace (V) as an omnibus multivariate analysis of variance (MANOVA) test statistic for its superior robustness to heterogeneous variances. J. Stevens (1979, 1980) contends that the robustness of V, Wilk's lambda (W) and the Hotelling-Lawley trace (T) are similar, and that their power functions are highly sensitive to slight covariance inequalities. Yet under conditions of diffuse noncentrality structures, V is a clear choice. A Monte Carlo simulation of V, W, and T as omnibus tests under conditions of covariance heterogeneity and variance homogeneity investigates the robustness of each test. Conditions of concentrated covariance and noncentrality structure were imposed to compare power. Results indicate that the assumption of homogeneous variance-covariance matrices in the form of covariance inequalities does not affect the robustness of V, W, or T, while T is slightly more powerful under such conditions. Five tables are included. (Contains 14 references.) (Author/SLD)
Journal of Stroke and Cerebrovascular Diseases, 2014
Background-In the setting of acute ischemic stroke (AIS), leukocytosis has been shown to be an in... more Background-In the setting of acute ischemic stroke (AIS), leukocytosis has been shown to be an indicator of inflammatory response. Although leukocytosis on admission has been shown to correlate with initial stroke severity in AIS patients, no work has been done to assess if there are differences in transient or persistent leukocytosis in patients without infection. The objective of this study is to determine the clinical significance of persistent versus transient leukocytosis during the early phase of AIS. Methods-Patients who presented with AIS to our center within 48 hours of symptom onset between July 2008 and June 2010 were retrospectively identified by chart review. Patients were included if they had leukocytosis on admission (defined as white blood cell count >11,000/μL based on laboratory reference range values). A logistic regression model was used to evaluate persistent leukocytosis (leukocytosis 48 hours after admission) as a predictor of several outcome measures, including good functional outcome (discharge modified Rankin Scale score of 0-2). Marginal effects were used to estimate the probability of poor functional outcome. Results-Of the 438 patients screened, 49 had leukocytosis on admission and of those 24 (49%) had persistent leukocytosis. NIHSS score correlated significantly with persistence of leukocytosis
In a mediation model, the a coefficient represents the relationship of the independent variable (... more In a mediation model, the a coefficient represents the relationship of the independent variable (X) to the mediator (Z) and the b coefficient represents the partial relationship of the mediator (Z) to the outcome (Y). The amount of mediation can be estimated as the product of the two sample coefficients (ab). Although it would seem that an increase in a would increase statistical power for product tests, it also increases the standard error of the product tests due to the necessary increase in the collinearity between X and Z. Thus, power can actually be decline with increases in a.
Journal of Modern Applied Statistical Methods, 2004
Data simulation was used to investigate whether tests performed on aligned ranks (Beasley, 2002) ... more Data simulation was used to investigate whether tests performed on aligned ranks (Beasley, 2002) could be used as robust alternatives to parametric methods for testing a split-plot interaction with non-normal data and heterogeneous covariance matrices. Results indicated the aligned rank method do not have any distinct advantage over parametric methods in this situation.
Improved identification of sternal injuries with multi-detector computed tomography (MDCT): sagittal reconstructions
Clinical Imaging, 2016
Chest computed tomography is acquired in the axial plane, but sternal injuries may be missed on a... more Chest computed tomography is acquired in the axial plane, but sternal injuries may be missed on axial images. This study hypothesized that sagittal sternal reconstruction images improve detection of sternal injury and radiologist&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s confidence in diagnosis compared to axial images. Five radiologists independently reviewed first axial images and on a different day sagittal images of a retrospective set of trauma cases recording presence/absence of a sternal injury and/or adjacent hematoma. The reviewer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s confidence in the presence/absence of a sternal injury was assessed on a 5-point scale. Sagittal reconstructions generally yielded higher interreader agreement and confidence indices on statistical analysis.
Southern Medical Journal, 2013
Objectives-To determine whether prolonged length of stay (pLOS) in ischemic stroke is related to ... more Objectives-To determine whether prolonged length of stay (pLOS) in ischemic stroke is related to delays in discharge disposition arrangement. Methods-We designed a retrospective study to compare patients with acute ischemic stroke (AIS) who experienced pLOS to those who did not experience pLOS. Patients who have had AIS between July 2008 and December 2010 were included unless they arrived >48 hours after time last seen normal, had an unknown last seen normal, or experienced an in-hospital stroke. pLOS was defined in our prospective stroke registry (before the generation of this research question) as hospitalization extended for ≥24 hours more than necessary to determine neurologic stability and next level of care/disposition for a given patient. We characterized the frequency of each cause of pLOS and further investigated the destinations that were more frequently associated with pLOS among patients with delay resulting from arranging discharge disposition. Results-Of the 274 patients included, 106 (31.9%) had pLOS. Reasons for pLOS were discharge disposition (48.1%), non-neurologic medical complications (36.8%), delays in imaging studies (20.8%), awaiting procedure (10.4%), and neurologic complications (9.4%). Among patients with pLOS caused by delayed disposition, more than half were awaiting placement in an inpatient rehabilitation facility. Conclusions-For the majority of our patients, pLOS was caused by acquired medical complications and delayed disposition, most commonly inpatient rehabilitation. Further efforts are needed to prevent complications and further investigation is necessary to identify the factors that may contribute to delayed discharge to inpatient rehabilitation facilities, which may include delayed planning or heightened scrutiny of insurance companies regarding their beneficiaries. Keywords stroke; inpatient rehabilitation; length of stay; complications; discharge disposition Advances in treatment of acute stroke and inpatient management have successfully lowered the stroke mortality rate. 1 In addition, these advances have resulted in improved outcomes for patients with ischemic stroke. 2 Although a decline in stroke incidence has been demonstrated, 3 the actual number of strokes each year is increasing because more people are
Abstract: A study involving 109 male and 116 female high achieving high school students (ages 16-... more Abstract: A study involving 109 male and 116 female high achieving high school students (ages 16-18) and their parents investigated the causal linkages among home environment, self-concepts, prior ability, and socioeconomic status on mathematics achievement, ...
A Meta-Analytic Validation of the Dunn and Dunn Model of Learning-Style Preferences
The Journal of Educational Research, 1995
... that learn ing-styles-based instruction was one of the few strategies that had impacted posit... more ... that learn ing-styles-based instruction was one of the few strategies that had impacted positively on the achievement of classi fied special education students (Alberg, Cook, Fiore, Friend, Sano, 1992). Similar gains were found by Stone (1992) with learning-disabled elementary ...
What is the impact on scale reliability and exploratory factor analysis of a Pearson correlation matrix when some respondents are not able to follow the rating …
annual meeting of the …, 2003
... Ferguson, &amp;amp;amp; Joreskog, 1987; Bernstein &amp;amp;amp; Teng, 1989; DiStefano... more ... Ferguson, &amp;amp;amp; Joreskog, 1987; Bernstein &amp;amp;amp; Teng, 1989; DiStefano, 2002; Green, Akey, Fleming, Hershberger, &amp;amp;amp; Marquis, 1997; Muthen &amp;amp;amp; Kaplan, 1985). ... Beasley, 1992; Franklin, SB , Gibson, DJ, Robertson, PA, Pohlmann, JT &amp;amp;amp; Fralish, JS, 1995). ...
Multiple Regression Approach to Analyzing Contingency Tables: Post Hoc and Planned Comparison Procedures
The Journal of Experimental Education, 1995
... 64( 1 ), 79-93 Multiple Regression Approach to Analyzing Contingency Tables: Post Hoc and Pla... more ... 64( 1 ), 79-93 Multiple Regression Approach to Analyzing Contingency Tables: Post Hoc and Planned Comparison Procedures T. MARK BEASLEY St. John&amp;#x27;s University RANDALL E.SCHUMACKER University of North Texas ABSTRACT. ... Page 3. Beasley &amp;amp; Schumacker 81 ...
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Papers by Timothy Beasley