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Biostatistics

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Selected Works

2016

Articles 1 - 9 of 9

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Adaptive Pre-Specification In Randomized Trials With And Without Pair-Matching, Laura Balzer, M. Van Der Laan, M. Petersen, The Search Collaboration Nov 2016

Adaptive Pre-Specification In Randomized Trials With And Without Pair-Matching, Laura Balzer, M. Van Der Laan, M. Petersen, The Search Collaboration

Laura B. Balzer

In randomized trials, adjustment for measured covariates during the analysis can reduce variance and increase power. To avoid misleading inference, the analysis plan must be pre-specified. However, it is often unclear a priori which baseline covariates (if any) should be adjusted for in the analysis.  Consider, for example, the Sustainable East Africa Research in Community Health (SEARCH) trial for HIV prevention and treatment.  There are 16 matched pairs of communities and many potential adjustment variables, including region, HIV prevalence, male circumcision coverage and measures of community-level viral load.  In this paper, we propose a rigorous procedure to data-adaptively select the …

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Correlates Of Hiv Acquisition In A Cohort Of Black Men Who Have Sex With Men In The United States: Hiv Prevention Trials Network (Hptn) 061, Beryl A. Koblin, Kenneth H. Mayer, Susan H. Eshleman, Lei Wang, Sharon B. Mannheimer, Carlos Del Rio, Steve Shoptaw, Manya Magnus, Susan Buchbinder, Leo Wilton, Ting-Yuan Liu, Vanessa Cummings, Estelle Piwowar-Manning, Sheldon D. Fields, Sam Griffith, Vanessa Elharrar, Darrell Wheeler Nov 2016

Correlates Of Hiv Acquisition In A Cohort Of Black Men Who Have Sex With Men In The United States: Hiv Prevention Trials Network (Hptn) 061, Beryl A. Koblin, Kenneth H. Mayer, Susan H. Eshleman, Lei Wang, Sharon B. Mannheimer, Carlos Del Rio, Steve Shoptaw, Manya Magnus, Susan Buchbinder, Leo Wilton, Ting-Yuan Liu, Vanessa Cummings, Estelle Piwowar-Manning, Sheldon D. Fields, Sam Griffith, Vanessa Elharrar, Darrell Wheeler

Leo Wilton

Background

Black men who have sex with men (MSM) in the United States (US) are affected by HIV at disproportionate rates compared to MSM of other race/ethnicities. Current HIV incidence estimates in this group are needed to appropriately target prevention efforts.

Methods

From July 2009 to October 2010, Black MSM reporting unprotected anal intercourse with a man in the past six months were enrolled and followed for one year in six US cities for a feasibility study of a multi-component intervention to reduce HIV infection. HIV incidence based on HIV seroconversion was calculated as number of events/100 person-years. Multivariate proportional …

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Targeted Estimation And Inference For The Sample Average Treatment Effect In Trials With And Without Pair-Matching, Laura Balzer, M. Petersen, M. Van Der Laan, The Search Collaboration Oct 2016

Targeted Estimation And Inference For The Sample Average Treatment Effect In Trials With And Without Pair-Matching, Laura Balzer, M. Petersen, M. Van Der Laan, The Search Collaboration

Laura B. Balzer

In cluster randomized trials, the study units usually are not a simple random sample from some clearly defined
target population. Instead, the target population tends to be hypothetical or ill-defined, and the selection of study
units tends to be systematic, driven by logistical and practical considerations. As a result, the population average
treatment effect (PATE) may be neither well-defined nor easily interpretable. In contrast, the sample average
treatment effect (SATE) is the mean difference in the counterfactual outcomes for the study units. The sample
parameter is easily interpretable and arguably the most relevant when the study units are not sampled …

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Performance-Constrained Binary Classification Using Ensemble Learning: An Application To Cost-Efficient Targeted Prep Strategies, Wenjing Zheng, Laura Balzer, Maya L. Petersen, Mark J. Van Der Laan Oct 2016

Performance-Constrained Binary Classification Using Ensemble Learning: An Application To Cost-Efficient Targeted Prep Strategies, Wenjing Zheng, Laura Balzer, Maya L. Petersen, Mark J. Van Der Laan

Laura B. Balzer

Binary classifications problems are ubiquitous in health and social science applications. In many cases, one wishes to balance two conflicting criteria for an optimal binary classifier. For instance, in resource-limited settings, an HIV prevention program based on offering Pre-Exposure Prophylaxis (PrEP) to select high-risk individuals must balance the sensitivity of the binary classifier in detecting future seroconverters (and hence offering them PrEP regimens) with the total number of PrEP regimens that is financially and logistically feasible for the program to deliver. In this article, we consider a general class of performance-constrained binary classification problems wherein the objective function and the …

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Estimating Effects With Rare Outcomes And High Dimensional Covariates: Knowledge Is Power, Laura Balzer, J. Ahern, S. Galea, M. Van Der Laan Sep 2016

Estimating Effects With Rare Outcomes And High Dimensional Covariates: Knowledge Is Power, Laura Balzer, J. Ahern, S. Galea, M. Van Der Laan

Laura B. Balzer

Many of the secondary outcomes in observational studies and randomized trials are rare. Methods for estimating causal effects and associations with rare outcomes, however, are limited, and this represents a missed opportunity for investigation. In this article, we construct a new targeted minimum loss-based estimator (TMLE) for the effect or association of an exposure on a rare outcome. We focus on the causal risk difference and statistical models incorporating bounds on the conditional mean of the outcome, given the exposure and measured confounders. By construction, the proposed estimator constrains the predicted outcomes to respect this model knowledge. Theoretically, this bounding …

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Targeted Estimation Of Marginal Absolute And Relative Associations In Case-Control Data: An Application In Social Epidemiology, M. Pearl, Laura Balzer, J. Ahern Aug 2016

Targeted Estimation Of Marginal Absolute And Relative Associations In Case-Control Data: An Application In Social Epidemiology, M. Pearl, Laura Balzer, J. Ahern

Laura B. Balzer

Background: Case-control studies are useful for rare outcomes, but typical analyses limit investigators to parametric estimation of conditional odds ratios. Several methods exist for obtaining marginal risk differences and risk ratios in a case-control setting, including a recently described semiparametric targeted approach optimized for rare outcomes.
Methods: Using case-control data from a study of neighborhood poverty and very preterm birth, we demonstrate estimation of marginal risk differences and risk ratios and compare a parametric substitution estimator based on maximum likelihood estimation with targeted maximum likelihood estimation (TMLE), and a refinement of TMLE for rare outcomes that incorporates bounds on the …

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Introduction To Targeted Learning, Laura Balzer Dec 2015

Introduction To Targeted Learning, Laura Balzer

Laura B. Balzer

No abstract provided.

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Early Diagnosis Of Dengue Disease Severity In A Resource-Limited Asian Country, Philippe Cavailler, Arnaud Tarantola, Yee Sin Leo, Andrew A. Lover, Anne Rachline, Duch Moniboth, Rekol Huy, Ai Li Quake, Kdan Yuvatha, Veasna Duong, Jeremy L. Brett, Philippe Buchy Dec 2015

Early Diagnosis Of Dengue Disease Severity In A Resource-Limited Asian Country, Philippe Cavailler, Arnaud Tarantola, Yee Sin Leo, Andrew A. Lover, Anne Rachline, Duch Moniboth, Rekol Huy, Ai Li Quake, Kdan Yuvatha, Veasna Duong, Jeremy L. Brett, Philippe Buchy

Andrew Lover

Background: Dengue is endemic throughout Cambodia, a country faced with significant health and economic challenges. We undertook a clinical study at the National Paediatric Hospital in Phnom Penh to evaluate clinical diagnostic parameters for dengue and predictors of disease outcome. Methods: Between September 2011 and January 2013, all consecutive inpatients aged between 1 and 15 years and presenting with suspected dengue were enrolled. They were clinically assessed using both the 1997 and 2009 WHO dengue classifications. Specimens were collected upon admission and discharge and tested for dengue at Institut Pasteur in Cambodia. Results: A total of 701 patients were screened. …

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Serological Evidence For Localized And Persistent Antibody Response In Zika Virus-Positive Neonates With Microcephaly (Brazil, 2015)- A Secondary Analysis, Andrew A. Lover Dec 2015

Serological Evidence For Localized And Persistent Antibody Response In Zika Virus-Positive Neonates With Microcephaly (Brazil, 2015)- A Secondary Analysis, Andrew A. Lover

Andrew Lover

A recent publication in The Lancet by Cordeiro and colleagues reported levels of IgM for Zika (ZIKV) and dengue (DENV) viruses in serum and cerebrospinal fluid (CSF) of 31 infants born with microcephaly in Brazil. 1 Their study suggests higher titers in CSF relative to serum in individual neonates, but no quantitative comparisons were reported. In this short report, the differences in antibody titers are quantified and compared between sample sources; across sampling periods; and between sample sources within individual neonates to more comprehensively understand these data to inform serological surveillance. These are statistically significant differences in ZIKV titers between …

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