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Full-Text Articles in Physical Sciences and Mathematics
Pragmatic Estimation Of A Spatio-Temporal Air Quality Model With Irregular Monitoring Data, Paul D. Sampson, Adam A. Szpiro, Lianne Sheppard, Johan Lindström, Joel D. Kaufman
Pragmatic Estimation Of A Spatio-Temporal Air Quality Model With Irregular Monitoring Data, Paul D. Sampson, Adam A. Szpiro, Lianne Sheppard, Johan Lindström, Joel D. Kaufman
UW Biostatistics Working Paper Series
Statistical analyses of the health effects of air pollution have increasingly used GIS-based covariates for prediction of ambient air quality in “land-use” regression models. More recently these regression models have accounted for spatial correlation structure in combining monitoring data with land-use covariates. The current paper builds on these concepts to address spatio-temporal prediction of ambient concentrations of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5) on the basis of a model representing spatially varying seasonal trends and spatial correlation structures. Our hierarchical methodology provides a pragmatic approach that fully exploits regulatory and other supplemental monitoring data which jointly …
Is Survival The Only Or Even The Right Outcome For Evaluating Treatments For Out-Of-Hospital Cardiac Arrest? A Proposed Test Based On Both An Intermediate And Ultimate Outcome., Al Hallstrom
UW Biostatistics Working Paper Series
It is generally agreed that the goal of resuscitation is survival with neurological and physiological status similar to that preceding the cardiac arrest. Previously I have argued that the lack of improvement in outcome from resuscitation over the past 3 to 4 decades, as compared to the substantial progress made in treatment of ischemic heart disease, is a consequence of the absence of randomized clinical trials of new interventions and the use of intermediate endpoints such as return of spontaneous circulation or admittance to hospital. Proponents of these intermediate endpoints have argued that those involved in the resuscitation have no …
Robustness Of Semiparametric Efficiency In Nearly-Correct Models For Two-Phase Samples, Thomas Lumley
Robustness Of Semiparametric Efficiency In Nearly-Correct Models For Two-Phase Samples, Thomas Lumley
UW Biostatistics Working Paper Series
Augmented inverse-probability weighted (AIPW) estimators for incomplete-data models typically do not have full semiparametric efficiency, but do have model-robustness properties not shared by the efficient estimator. We examine the performance of efficient and AIPW estimators when the complete-data model is nearly correctly specified, in the sense that the misspecification is not reliably detectable from the data by any possible diagnostic or test. Asymptotic results for these nearly true models are obtained by representing them as sequences of misspecified models that are mutually contiguous with a correctly specified model. For some least favorable direction of model misspecification the bias in the …
Nonparametric And Semiparametric Estimation Of The Three Way Receiver Operating Characteristic Surface, Jialiang Li, Xiao-Hua Zhou
Nonparametric And Semiparametric Estimation Of The Three Way Receiver Operating Characteristic Surface, Jialiang Li, Xiao-Hua Zhou
UW Biostatistics Working Paper Series
In many situations the diagnostic decision is not limited to a binary choice. Binary statistical tools such as receiver operating characteristic (ROC) curve and area under the ROC curve (AUC) need to be expanded to address three-category classification problem. Previous authors have suggest various ways to model the extension of AUC but not the ROC surface. Only simple parametric approaches are proposed for modeling the ROC measure under the assumption that test results all follow normal distributions. We study the estimation methods of three dimensional ROC surfaces with nonparametric and semiparametric estimators. Asymptotical results are provided as a basis for …
Evaluating Markers For Treatment Selection Based On Survival Time, Xiao Song, Xiao-Hua Zhou
Evaluating Markers For Treatment Selection Based On Survival Time, Xiao Song, Xiao-Hua Zhou
UW Biostatistics Working Paper Series
For many medical conditions several treatment options may be available for treating patients. We consider evaluating markers based on a simple treatment selection policy that incorporates information on the patient's marker value exceeding a threshold. For example, colon cancer patients may be treated by surgery alone or surgery plus chemotherapy. The c-myc gene expression level may be used as a biomarker for treatment selection. Although traditional regression methods may assess the effect of the marker and treatment on outcomes, it is appealing to quantify more directly the potential impact on the population of using the marker to select treatment. A …
Interval Estimation For The Difference In Paired Areas Under The Roc Curves In The Absence Of A Gold Standard Test, Hsin-Neng Hsieh, Hsiu-Yuan Su, Xiao-Hua Zhou
Interval Estimation For The Difference In Paired Areas Under The Roc Curves In The Absence Of A Gold Standard Test, Hsin-Neng Hsieh, Hsiu-Yuan Su, Xiao-Hua Zhou
UW Biostatistics Working Paper Series
Receiver operating characteristic (ROC) curves can be used to assess the accuracy of tests measured on ordinal or continuous scales. The most commonly used measure for the overall diagnostic accuracy of diagnostic tests is the area under the ROC curve (AUC). A gold standard test on the true disease status is required to estimate the AUC. However, a gold standard test may sometimes be too expensive or infeasible. Therefore, in many medical research studies, the true disease status of the subjects may remain unknown. Under the normality assumption on test results from each disease group of subjects, using the expectation-maximization …
A Semi-Parametric Two-Part Mixed-Effects Heteroscedastic Transformation Model For Correlated Right-Skewed Semi-Continuous Data, Huazhen Lin, Xiao-Hua Zhou
A Semi-Parametric Two-Part Mixed-Effects Heteroscedastic Transformation Model For Correlated Right-Skewed Semi-Continuous Data, Huazhen Lin, Xiao-Hua Zhou
UW Biostatistics Working Paper Series
In longitudinal or hierarchical structure studies, we often encounter a semi-continuous variable that has a certain proportion of a single value and a continuous and skewed distribution among the rest of values. In the paper, we propose a new semi-parametric two-part mixed-effects transformation model to fit correlated skewed semi-continuous data. In our model, we allow the transformation to be non-parametric. Fitting the proposed model faces computational challenges due to intractable numerical integrations. We derive the estimates for the parameter and the transformation function based on an approximate likelihood, which has high order accuracy but less computational burden. We also propose …
Relaxing Latent Ignorability In The Itt Analysis Of Randomized Studies With Missing Data And Noncompliance, L Taylor, Xiao-Hua Zhou
Relaxing Latent Ignorability In The Itt Analysis Of Randomized Studies With Missing Data And Noncompliance, L Taylor, Xiao-Hua Zhou
UW Biostatistics Working Paper Series
Abstract: In this paper we consider the problem in causal inference of estimating the local complier average causal effect (CACE) parameter in the setting of a randomized clinical trial with a binary outcome, cross-over noncompliance, and unintentional missing data on the responses. We focus on the development of a moment estimator that relaxes the assumption of latent ignorability and incorporates sensitivity parameters that represent the relationship between potential outcomes and associated potential response indicators. If conclusions are insensitive over a range of logically possible values of the sensitivity parameters, then the number of interpretations of the data is reduced, and …
Multiple Imputation Methods For Treatment Noncompliance And Nonresponse In Randomized Clinical Trials, Leslie Taylor, Xiao-Hua (Andrew) Zhou
Multiple Imputation Methods For Treatment Noncompliance And Nonresponse In Randomized Clinical Trials, Leslie Taylor, Xiao-Hua (Andrew) Zhou
UW Biostatistics Working Paper Series
Summary: Randomized clinical trials are a powerful tool for investigating causal treatment effects, but in human trials there are oftentimes problems of noncompliance which standard analyses, such as the intention-to-treat or as-treated analysis, either ignore or incorporate in such a way that the resulting estimand is no longer a causal effect. One alternative to these analyses is the complier average causal effect (CACE) which estimates the average causal treatment effect among a subpopulation that would comply under any treatment assigned. We focus on the setting of a randomized clinical trial with crossover treatment noncompliance (e.g., control subjects could receive the …
Semiparametric Two-Part Models With Proportionality Constraints: Analysis Of The Multi-Ethnic Study Of Atherosclerosis (Mesa), Anna Liu, Richard Kronmal, Xiao-Hua Zhou, Shuangge Ma
Semiparametric Two-Part Models With Proportionality Constraints: Analysis Of The Multi-Ethnic Study Of Atherosclerosis (Mesa), Anna Liu, Richard Kronmal, Xiao-Hua Zhou, Shuangge Ma
UW Biostatistics Working Paper Series
SUMMARY. In this article, we analyze the coronary artery calcium (CAC) score in the Multi-Ethnic Study of Atherosclerosis (MESA), where about half of the CAC scores are zero and the rest are continuously distributed. When the observed data has a mixture distribution, two-part models can be the natural choice. With a two-part model, there are two covariate effects, with one in each part of the model. Determination of whether the two covariate effects are proportional can provide more insights into the process underlying development and progression of CAC. In this study, we model the CAC score using a semiparametric two-part …
Pooled Nucleic Acid Testing To Identify Antiretroviral Treatment Failure During Hiv Infection, Susanne May, Anthony Gamst, Richard Haubrich, Constance Benson, Davey Smith
Pooled Nucleic Acid Testing To Identify Antiretroviral Treatment Failure During Hiv Infection, Susanne May, Anthony Gamst, Richard Haubrich, Constance Benson, Davey Smith
UW Biostatistics Working Paper Series
Abstract Background: Pooling strategies have been used to reduce the costs of polymerase chain reaction based screening for acute HIV infection in populations where the prevalence of acute infection is low (<1%). Only limited research has been done for conditions where the prevalence of screening positivity is higher (>1%). Methods and Results: We present data on a variety of pooling strategies that incorporate the use of PCR-based quantitative measures to monitor for virologic failure among HIV-infected patients receiving antiretroviral therapy. For a prevalence of virologic failure between 1% and 25%, we demonstrate relative efficiency and accuracy of various strategies. These results could be used to choose the best strategy based on the requirements of individual laboratory …
Measures To Summarize And Compare The Predictive Capacity Of Markers, Wen Gu, Margaret Pepe
Measures To Summarize And Compare The Predictive Capacity Of Markers, Wen Gu, Margaret Pepe
UW Biostatistics Working Paper Series
The predictive capacity of a marker in a population can be described using the population distribution of risk (Huang et al., 2007; Pepe et al., 2008a; Stern, 2008). Virtually all standard statistical summaries of predictability and discrimination can be derived from it (Gail and Pfeiffer, 2005). The goal of this paper is to develop methods for making inference about risk prediction markers using summary measures derived from the risk distribution. We describe some new clinically motivated summary measures and give new interpretations to some existing statistical measures. Methods for estimating these summary measures are described along with distribution theory that …