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596 results on '"Lai, Dejian"'

175. Long-Term Effectiveness of Accelerated Hepatitis B Vaccination Schedule in Drug Users.

Author

Shah, Dimpy P., Grimes, Carolyn Z., Nguyen, Anh T., Lai, Dejian, and Hwang, Lu-Yu

Abstract

Objectives. We demonstrated the effectiveness of an accelerated hepatitis B vaccination schedule in drug users. Methods. We compared the long-term effectiveness of accelerated (0–1–2 months) and standard (0–1–6 months) hepatitis B vaccination schedules in preventing hepatitis B virus (HBV) infections and anti-hepatitis B (anti-HBs) antibody loss during 2-year follow-up in 707 drug users (HIV and HBV negative at enrollment and completed 3 vaccine doses) from February 2004 to October 2009. Results. Drug users in the accelerated schedule group had significantly lower HBV infection rates, but had a similar rate of anti-HBs antibody loss compared with the standard schedule group over 2 years of follow-up. No chronic HBV infections were observed. Hepatitis C positivity at enrollment and age younger than 40 years were independent risk factors for HBV infection and antibody loss, respectively. Conclusions. An accelerated vaccination schedule was more preferable than a standard vaccination schedule in preventing HBV infections in drug users. To overcome the disadvantages of a standard vaccination schedule, an accelerated vaccination schedule should be considered in drug users with low adherence. Our study should be repeated in different cohorts to validate our findings and establish the role of an accelerated schedule in hepatitis B vaccination guidelines for drug users. [ABSTRACT FROM AUTHOR]

Published
2015
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176. Stochastically Curtailed Tests Under Fractional Brownian Motion.

Author

Zhang, Qiang, Lai, Dejian, and Davis, Barry R.

Subjects
*STOCHASTIC analysis, *FRACTIONAL calculus, *BROWNIAN motion, *GROUP theory, *ERROR rates
Abstract

Stochastic curtailment has been considered for the interim monitoring of group sequential trials (Davis and Hardy, 1994). Statistical boundaries in Davis and Hardy (1994) were derived using theory of Brownian motion. In some clinical trials, the conditions of forming a Brownian motion may not be satisfied. In this paper, we extend the computations of Brownian motion based boundaries, expected stopping times, and type I and type II error rates to fractional Brownian motion (FBM). FBM includes Brownian motion as a special case. Designs under FBM are compared to those under Brownian motion and to those of O’Brien–Fleming type tests. One- and two-sided boundaries for efficacy and futility monitoring are also discussed. Results show that boundary values decrease and error rates deviate from design levels when the Hurst parameter increases from 0.1 to 0.9, these changes should be considered when designing a study under FBM. [ABSTRACT FROM PUBLISHER]

Published
2015
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177. Comparison of Statistical Methods for Pretest–Posttest Designs in Terms of Type I Error Probability and Statistical Power.

Author

Wu, Xionghua Wilson and Lai, Dejian

Subjects
*STATISTICAL errors, *PROBABILITY theory, *STATISTICAL power analysis, *ANALYSIS of variance, *DATA transformations (Statistics), *ROBUST statistics
Abstract

The pretest–posttest design is widely used to investigate the effect of an experimental treatment in biomedical research. The treatment effect may be assessed using analysis of variance (ANOVA) or analysis of covariance (ANCOVA). The normality assumption for parametric ANOVA and ANCOVA may be violated due to outliers and skewness of data. Nonparametric methods, robust statistics, and data transformation may be used to address the nonnormality issue. However, there is no simultaneous comparison for the four statistical approaches in terms of empirical type I error probability and statistical power. We studied 13 ANOVA and ANCOVA models based on parametric approach, rank and normal score-based nonparametric approach, Huber M-estimation, and Box–Cox transformation using normal data with and without outliers and lognormal data. We found that ANCOVA models preserve the nominal significance level better and are more powerful than their ANOVA counterparts when the dependent variable and covariate are correlated. Huber M-estimation is the most liberal method. Nonparametric ANCOVA, especially ANCOVA based on normal score transformation, preserves the nominal significance level, has good statistical power, and is robust for data distribution. [ABSTRACT FROM AUTHOR]

Published
2015
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193. Identification of Bone Marrow Cell Subpopulations Associated with Improved Functional Outcomes in Patients with Chronic Left Ventricular Dysfunction: An Embedded Cohort Evaluation of the FOCUS-CCTRN Trial

Author

Taylor, Doris A., Perin, Emerson C., Willerson, James T., Zierold, Claudia, Resende, Micheline, Carlson, Marjorie, Nestor, Belinda, Wise, Elizabeth, Orozco, Aaron, Pepine, Carl J., Henry, Timothy D., Ellis, Stephen G., Zhao, David X. M., Traverse, Jay H., Cooke, John P., Schutt, Robert C., Bhatnagar, Aruni, Grant, Maria B., Lai, Dejian, Johnstone, Brian H., Sayre, Shelly L., Moyé, Lem, Ebert, Ray F., Bolli, Roberto, Simari, Robert D., and Cogle, Christopher R.

Abstract

In the current study, we sought to identify bone marrow-derived mononuclear cell (BM-MNC) subpopulations associated with a combined improvement in left ventricular ejection fraction (LVEF), left ventricular end-systolic volume (LVESV), and maximal oxygen consumption (VO2max) in patients with chronic ischemic cardiomyopathy 6 months after receiving transendocardial injections of autologous BM-MNCs or placebo. For this prospectively planned analysis, we conducted an embedded cohort study comprising 78 patients from the FOCUS-Cardiovascular Cell Therapy Research Network (CCTRN) trial. Baseline BM-MNC immunophenotypes and progenitor cell activity were determined by flow cytometry and colony-forming assays, respectively. Previously stable patients who demonstrated improvement in LVEF, LVESV, and VO2max during the 6-month course of the FOCUS-CCTRN study (group 1, n= 17) were compared to those who showed no change or worsened in one to three of these endpoints (group 2, n= 61) and to a subset of patients from group 2 who declined in all three functional endpoints (group 2A, n= 11). Group 1 had higher frequencies of B-cell and CXCR4+BM-MNC subpopulations at study baseline than group 2 or 2A. Furthermore, patients in group 1 had fewer endothelial colony-forming cells and monocytes/macrophages in their bone marrow than those in group 2A. To our knowledge, this is the first study to show that in patients with ischemic cardiomyopathy, certain bone marrow-derived cell subsets are associated with improvement in LVEF, LVESV, and VO2max at 6 months. These results suggest that the presence of both progenitor and immune cell populations in the bone marrow may influence the natural history of chronic ischemic cardiomyopathy—even in stable patients. Thus, it may be important to consider the bone marrow composition and associated regenerative capacity of patients when assigning them to treatment groups and evaluating the results of cell therapy trials.

Published
2016
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194. Evaluating narrow windows of maternal exposure to ozone and preterm birth in a large urban area in Southeast Texas

Author

Symanski, Elaine, McHugh, Michelle K, Zhang, Xuan, Craft, Elena S, and Lai, Dejian

Abstract

The association between O3exposure and preterm birth (PTB) remains unclear. We evaluated associations for three categories of PTB and O3in Harris County, Texas, during narrow periods of gestation. We computed two sets of exposure metrics during every 4 weeks of pregnancy for 152,214 mothers who delivered singleton, live-born infants in 2005–2007, accounting first for temporal variability and then for temporal and spatial sources of variability in ambient O3levels. Associations were assessed using multiple logistic regression. We also examined the potential for a fixed cohort bias. In the bias-corrected cohort where associations were somewhat stronger, elevated odds ratios (ORs) per 10 parts per billion increase in O3exposure (county-level metric) were detected for the fifth (OR=1.08, 95% confidence interval (CI): 1.04–1.12), sixth (OR=1.05, 95% CI=1.01–1.09), and seventh (OR=1.07, 95% CI=1.03–1.10) 4-week periods of pregnancy for late PTB (33–36 completed weeks gestation), the fifth (OR=1.13, 95% CI=1.02–1.25) and seventh (OR=1.15, 95% CI=1.04–1.27) 4-week periods of pregnancy for moderate PTB (29–32 completed weeks gestation), and the fifth (OR=1.21, 95% CI=1.08–1.36) 4-week period of pregnancy for severe PTB (20–28 completed weeks gestation). Conversely, decreased odds were found in the first 4-week period of pregnancy for severe PTB (OR=0.83, 95% CI=0.74–0.94). Associations were slightly attenuated using the spatially interpolated (kriged) metrics, and for women who did not work outside of the home. Our analyses confirm reports in other parts of the United States and elsewhere with findings that suggest that maternal exposure to ambient levels of O3is associated with PTB.

Published
2016
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