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- Data masking; Confidentiality; Spatial smoothing (1)
- Effective communication; Effective display; Confidence intervals (1)
- FMRI; GLM; Group analysis; Hierarchical model; Image analysis; Shrinkage estimation (1)
- Function of locally varying complexity; Hierarchical mixed model; Laplace approximation (1)
- Functional imaging; Image analyis; MCMC; Medical imaging (1)
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- Hierarchical model; Markov chain Monte Carlo; Multiple imputation; Disparity; Socioenonomic status (1)
- Hierarchical models; Interaction; PM10; Regression trees (1)
- Neuroimaging; Regions of interest (1)
- Survival analysis; Informative censoring; Interval censoring; Coarsening at random; Sensitivity analysis; EM algorithem; MCMC; Gibbs sampler; Data augmentation (1)
Articles 1 - 9 of 9
Full-Text Articles in Biostatistics
A Smoothing Approach To Data Masking, Yijie Zhous, Francesca Dominici, Thomas A. Louis
A Smoothing Approach To Data Masking, Yijie Zhous, Francesca Dominici, Thomas A. Louis
Johns Hopkins University, Dept. of Biostatistics Working Papers
Individual-level data are often not publicly available due to confidentiality. Instead, masked data are released for public use. However, analyses performed using masked data may produce invalid statistical results such as biased parameter estimates or incorrect standard errors. In this paper, we propose a data masking method using spatial smoothing, and we investigate the bias of parameter estimates resulting from analyses using the masked data for Generalized Linear Models (GLM). The method allows for varying both the form and the degree of masking by utilizing a smoothing weight function and a smoothness parameter. We show that data masking by using …
Effective Communication Of Standard Errors And Confidence Intervals, Thomas A. Louis, Scott L. Zeger
Effective Communication Of Standard Errors And Confidence Intervals, Thomas A. Louis, Scott L. Zeger
Johns Hopkins University, Dept. of Biostatistics Working Papers
We recommend a format for communicating an estimate with its standard error or confidence interval. The format reinforces that the associated variability is an inseparable component of the estimate and it substantially improves clarity in tabular displays.
Inference For Survival Curves With Informatively Coarsened Discrete Event-Time Data: Application To Alive, Michelle Shardell, Daniel O. Scharfstein, David Vlahov, Noya Galai
Inference For Survival Curves With Informatively Coarsened Discrete Event-Time Data: Application To Alive, Michelle Shardell, Daniel O. Scharfstein, David Vlahov, Noya Galai
Johns Hopkins University, Dept. of Biostatistics Working Papers
In many prospective studies, including AIDS Link to the Intravenous Experience (ALIVE), researchers are interested in comparing event-time distributions (e.g.,for human immunodeficiency virus seroconversion) between a small number of groups (e.g., risk behavior categories). However, these comparisons are complicated by participants missing visits or attending visits off schedule and seroconverting during this absence. Such data are interval-censored, or more generally,coarsened. Most analysis procedures rely on the assumption of non-informative censoring, a special case of coarsening at random that may produce biased results if not valid. Our goal is to perform inference for estimated survival functions across a small number of …
Identifying Effect Modifiers In Air Pollution Time-Series Studies Using A Two-Stage Analysis, Sandrah P. Eckel, Thomas A. Louis
Identifying Effect Modifiers In Air Pollution Time-Series Studies Using A Two-Stage Analysis, Sandrah P. Eckel, Thomas A. Louis
Johns Hopkins University, Dept. of Biostatistics Working Papers
Studies of the health effects of air pollution such as the National Morbidity and Mortality Air Pollution Study (NMMAPS) relate changes in daily pollution to daily deaths in a sample of cities and calendar years. Generally, city-specific estimates are combined into regional and national estimates using two-stage models. Our two-stage analysis identifies effect modifiers of the relation between single-day lagged PM10 and daily mortality in people age 65 and older from the 50 largest NMMAPS cities. We build on the standard approach by "fractionating" city-specific analyses to produce month-year-city specific estimated air pollution effects (slopes) in Stage I. In Stage …
Racial Disparities In Mortality Risks In A Sample Of The U.S. Medicare Population, Yijie Zhou, Francesca Dominici, Thomas A. Louis
Racial Disparities In Mortality Risks In A Sample Of The U.S. Medicare Population, Yijie Zhou, Francesca Dominici, Thomas A. Louis
Johns Hopkins University, Dept. of Biostatistics Working Papers
Racial disparities in mortality risks adjusted by socioeconomic status (SES) are not well understood. To add to the understanding of racial disparities, we construct and analyze a data set that links, at individual and zip code levels, three government databases: Medicare, Medicare Current Beneficiary Survey and U.S. Census. Our study population includes more than 4 million Medicare enrollees residing in 2095 zip codes in the Northeast region of U.S. We develop hierarchical models to estimate Black-White disparity in risk of death, adjusted by both individual-level and zip codelevel income. We define population-level attributable risk (AR), relative attributable risk (RAR) and …
A Case Study In Pharmacologic Imaging Using Principal Curves In Single Photon Emission Computed Tomography, Brian S. Caffo, Ciprian M. Crainiceanu, Lijuan Deng, Craig W. Hendrix
A Case Study In Pharmacologic Imaging Using Principal Curves In Single Photon Emission Computed Tomography, Brian S. Caffo, Ciprian M. Crainiceanu, Lijuan Deng, Craig W. Hendrix
Johns Hopkins University, Dept. of Biostatistics Working Papers
In this manuscript we are concerned with functional imaging of the colon to assess the kinetics of a microbicide lubricant. The overarching goal is to understand the distribution of the lubricant in the colon. Such information is crucial for understanding the potential impact of the microbicide on HIV viral transmission. The experiment was conducted by imaging a radiolabeled lubricant distributed in the subject’s colon. The tracer imaging was conducted via single photon emission computed tomography (SPECT), a non-invasive, in-vivo functional imaging technique. We develop a novel principal curve algorithm to construct a three dimensional curve through the colon images. The …
A Bayesian Hierarchical Framework For Spatial Modeling Of Fmri Data, F. Dubois Bowman, Brian S. Caffo, Susan Spear Bassett, Clinton Kilts
A Bayesian Hierarchical Framework For Spatial Modeling Of Fmri Data, F. Dubois Bowman, Brian S. Caffo, Susan Spear Bassett, Clinton Kilts
Johns Hopkins University, Dept. of Biostatistics Working Papers
Functional neuroimaging techniques enable investigations into the neural basis of human cognition, emotions, and behaviors. In practice, applications of functional magnetic resonance imaging (fMRI) have provided novel insights into the neuropathophysiology of major psychiatric,neurological, and substance abuse disorders, as well as into the neural responses to their treatments. Modern activation studies often compare localized task-induced changes in brain activity between experimental groups. One may also extend voxel-level analyses by simultaneously considering the ensemble of voxels constituting an anatomically defined region of interest (ROI) or by considering means or quantiles of the ROI. In this work we present a Bayesian extension …
Fast Adaptive Penalized Splines, Tatyana Krivobokova, Ciprian M. Crainiceanu, Goran Kauermann
Fast Adaptive Penalized Splines, Tatyana Krivobokova, Ciprian M. Crainiceanu, Goran Kauermann
Johns Hopkins University, Dept. of Biostatistics Working Papers
This paper proposes a numerically simple routine for locally adaptive smoothing. The locally heterogeneous regression function is modelled as a penalized spline with a smoothly varying smoothing parameter modelled as another penalized spline. This is being formulated as hierarchical mixed model, with spline coe±cients following a normal distribution, which by itself has a smooth structure over the variances. The modelling exercise is in line with Baladandayuthapani, Mallick & Carroll (2005) or Crainiceanu, Ruppert & Carroll (2006). But in contrast to these papers Laplace's method is used for estimation based on the marginal likelihood. This is numerically simple and fast and …
Modified Test Statistics By Inter-Voxel Variance Shrinkage With An Application To Fmri, Shu-Chih Su, Brian Caffo, Elizabeth Garrett-Mayer, Susan Bassett
Modified Test Statistics By Inter-Voxel Variance Shrinkage With An Application To Fmri, Shu-Chih Su, Brian Caffo, Elizabeth Garrett-Mayer, Susan Bassett
Johns Hopkins University, Dept. of Biostatistics Working Papers
Functional Magnetic Resonance Imaging (fMRI) is a non-invasive technique which is commonly used to quantify changes in blood oxygenation and flow coupled to neuronal activation. One of the primary goals of fMRI studies is to identify localized brain regions where neuronal activation levels vary between groups. Single voxel t-tests have been commonly used to determine whether activation related to the protocol differs across groups. Due to the generally limited number of subjects within each study, accurate estimation of variance at each voxel is difficult. Thus, combining information across voxels in the statistical analysis of fMRI data is desirable in order …