Statistics and Probability Commons^™

Estimating The Accuracy Of Polymerase Chain Reaction-Based Tests Using Endpoint Dilution, Jim Hughes, Patricia Totten

UW Biostatistics Working Paper Series

PCR-based tests for various microorganisms or target DNA sequences are generally acknowledged to be highly "sensitive" yet the concept of sensitivity is ill-defined in the literature on these tests. We propose that sensitivity should be expressed as a function of the number of target DNA molecules in the sample (or specificity when the target number is 0). However, estimating this "sensitivity curve" is problematic since it is difficult to construct samples with a fixed number of targets. Nonetheless, using serially diluted replicate aliquots of a known concentration of the target DNA sequence, we show that it is possible to disentangle …

Analysis Of Longitudinal Marginal Structural Models , Jennifer F. Bryan, Zhuo Yu, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

In this article we construct and study estimators of the causal effect of a time-dependent treatment on survival in longitudinal studies. We employ a particular marginal structural model (MSM), and follow a general methodology for constructing estimating functions in censored data models. The inverse probability of treatment weighted (IPTW) estimator is used as an initial estimator and the corresponding treatment-orthogonalized, one-step estimator is consistent and asymptotically linear when the treatment mechanism is consistently estimated. We extend these methods to handle informative censoring. A simulation study demonstrates that the the treatment-orthogonalized, one-step estimator is superior to the IPTW estimator in terms …

An Empirical Study Of Marginal Structural Models For Time-Independent Treatment, Tanya A. Henneman, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

In non-randomized treatment studies a significant problem for statisticians is determining how best to adjust for confounders. Marginal structural models (MSMs) and inverse probability of treatment weighted (IPTW) estimators are useful in analyzing the causal effect of treatment in observational studies. Given an IPTW estimator a doubly robust augmented IPTW (AIPTW) estimator orthogonalizes it resulting in a more e±cient estimator than the IPTW estimator. One purpose of this paper is to make a practical comparison between the IPTW estimator and the doubly robust AIPTW estimator via a series of Monte- Carlo simulations. We also consider the selection of the optimal …

The Analysis Of Placement Values For Evaluating Discriminatory Measures, Margaret S. Pepe, Tianxi Cai

UW Biostatistics Working Paper Series

The idea of using measurements such as biomarkers, clinical data, or molecular biology assays for classification and prediction is popular in modern medicine. The scientific evaluation of such measures includes assessing the accuracy with which they predict the outcome of interest. Receiver operating characteristic curves are commonly used for evaluating the accuracy of diagnostic tests. They can be applied more broadly, indeed to any problem involving classification to two states or populations (D = 0 or D = 1). We show that the ROC curve can be interpreted as a cumulative distribution function for the discriminatory measure Y in the …

Case-Control Current Status Data, Nicholas P. Jewell, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

Current status observation on survival times has recently been widely studied. An extreme form of interval censoring, this data structure refers to situations where the only available information on a survival random variable, T, is whether or not T exceeds a random independent monitoring time C, a binary random variable, Y. To date, nonparametric analyses of current status data have assumed the availability of i.i.d. random samples of the random variable (Y, C), or a similar random sample at each of a set of fixed monitoring times. In many situations, it is useful to consider a case-control sampling scheme. Here, …

Current Status Data: Review, Recent Developments And Open Problems, Nicholas P. Jewell, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

Researchers working with survival data are by now adept at handling issues associated with incomplete data, particular those associated with various forms of censoring. An extreme form of interval censoring, known as current status observation, refers to situations where the only available information on a survival random variable T is whether or not T exceeds a random independent monitoring time C. This article contains a brief review of the extensive literature on the analysis of current status data, discussing the implications of response-based sampling on these methods. The majority of the paper introduces some recent extensions of these ideas to …

Estimating Causal Parameters In Marginal Structural Models With Unmeasured Confounders Using Instrumental Variables, Tanya A. Henneman, Mark Johannes Van Der Laan, Alan E. Hubbard

U.C. Berkeley Division of Biostatistics Working Paper Series

For statisticians analyzing medical data, a significant problem in determining the causal effect of a treatment on a particular outcome of interest, is how to control for unmeasured confounders. Techniques using instrumental variables (IV) have been developed to estimate causal parameters in the presence of unmeasured confounders. In this paper we apply IV methods to both linear and non-linear marginal structural models. We study a specific class of generalized estimating equations that is appropriate to these data, and compare the performance of the resulting estimator to the standard IV method, a two-stage least squares procedure. Our results are applied to …

The Role Of Diet And Physical Activity For Ovarian Cancer Results From The Adventist Health Study, Fatemeh Kiani

Loma Linda University Electronic Theses, Dissertations & Projects

A few aspects of the epidemiology of ovarian cancer are well understood, such as the inverse relationship with parity and oral contraceptive (OC) use. The role of other factors such as the potential influence of diet or physical activity is far from being established. A few studies, however, have been able to identify dietary risk factors for ovarian cancer. In this dissertation, I have conducted two studies that investigate the relationship between dietary factors and physical activity and the three endpoints: 1) nonfatal ovarian cancer (1976-1982; time to diagnosis), 2) fatal ovarian cancer (1976-1988; time to death), and 3) total …

Body Weight And Mortality Among Adults Who Never Smoked, Pramil N. Singh

Loma Linda University Electronic Theses, Dissertations & Projects

Most prospective studies identify an increased mortality risk for adults of high body mass index (> 27 kg/m²) that is commonly attributed to the effects of excess body fat, and also identify an increased mortality risk for adults of low body mass index (< 21 kg/m²), an association that, if causal among healthy adults, is without adequate pathophysiologic support.

In this dissertation, I have conducted three studies that continue the investigation of adiposity in relation to mortality among never-smoking adults of the California Seventh-day Adventist population. Among never-smoking adults of the Adventist Mortality Study (1960-1985), the relation between …

Assessing The Accuracy Of A New Diagnostic Test When A Gold Standard Does Not Exist, Todd A. Alonzo, Margaret S. Pepe

UW Biostatistics Working Paper Series

Often the accuracy of a new diagnostic test must be assessed when a perfect gold standard does not exist. Use of an imperfect test biases the accuracy estimates of the new test. This paper reviews existing approaches to this problem including discrepant resolution and latent class analysis. Deficiencies with these approaches are identified. A new approach is proposed that combines the results of several imperfect reference tests to define a better reference standard. We call this the composite reference standard (CRS). Using the CRS, accuracy can be assessed using multistage sampling designs. Maximum likelihood estimates of accuracy and expressions for …

A Longitudinal Study Of Hospitalization Rates For Patients With Chronic Disease: Results From The Medical Outcomes Study., Eugene C. Nelson, Colleen A. Mchorney, Willard G. Manning, W H. Rogers

Dartmouth Scholarship

To prospectively compare inpatient and outpatient utilization rates between prepaid (PPD) and fee-for-service (FFS) insurance coverage for patients with chronic disease. Data from the Medical Outcomes Study, a longitudinal observational study of chronic disease patients conducted in Boston, Chicago, and Los Angeles.A four-year prospective study of resource utilization among 1,681 patients under treatment for hypertension, diabetes, myocardial infarction, or congestive heart failure in the practices of 367 clinicians.

Student Evaluations Of Teaching Effectiveness: The Interpretation Of Observational Data And The Principle Of Faute De Mieux, B. Burt Gerstman

Faculty Publications

Student opinion surveys are important but widely misunderstood tools for evaluating teaching effectiveness. In this brief review, an analogy is drawn between the use and interpretation of observational data for public health and biomedical research and the use of student opinion data in evaluating teach ing effectiveness. Sources of systematic error in the form of selection bias, information bias, and confounding are defined and illustrated. Original data concerning intermittent "quid pro quo" confounding (i.e., the effect of expected grades on student evaluations of teaching) are presented. Finally, the principle of faute de mieux ("lack of anything better") and the interpretation …

Diet And Colon Cancer Risk In The Population Of Thailand, Nithat Sirichotiratana

Loma Linda University Electronic Theses, Dissertations & Projects

Epidemiological studies have emphasized environmental influences, especially a diet high in animal fat and low in fiber, as major risk factors for colon cancer. In order to examine the relationship between dietary fat and fiber and occurrence of colon cancer, patient medical records from the National Cancer Institute between 1981-1991 were used for the first hospital-based case-control study of diet and colon cancer in Thailand. These records included a total of 168 cases and 357 controls. Data on the frequency consumption of various food items were obtained by using an existing food frequency questionnaire, completed as part of patient’s history …

Case-Control Study Of Vitamin A Intake And Colorectal Cancer In Seventh-Day Adventists, John William Morgan

Loma Linda University Electronic Theses, Dissertations & Projects

Colorectal cancer is the second most common cause of cancer deaths in Americans; producing approximately 60,000 deaths in Americans each year. Studies of high and low risk populations have suggested a dietary etiology for colorectal cancer, although investigations of specific dietary factors have produced inconsistent results.

Population based studies of California Seventh-day Adventists demonstrate dietary variety regarding factors suspected as important in the etiology of colorectal cancer. These studies document a substantially reduced mortality and incidence from colorectal cancer in Seventh-day Adventists when compared to other California Populations. Although specific reasons for this difference remain obscure, the 'Unique lifestyle and …

Chronic Respiratory Disease Symptom Effects Of Long-Term Cumulative Exposure To Passive Tobacco Smoke And To Ambient Levels Of Tsp, Oxidants, So2, And No2 In Southern California, Gary L. Euler

Loma Linda University Electronic Theses, Dissertations & Projects

To assess risk of chronic respiratory disease symptoms due to long-term exposure to the ambient levels of TSP, oxidants, SO2 and NO2 in photochemical air pollution, symptoms were ascertained using NHLBI questions on 8,572 Southern California Seventh-day Adventist, nonsmokers, 25 years and older, who lived eleven years or longer in their 1977 residential area. Tobacco smoke, active and passive, and occupational exposures were measured by questionnaires, as well as lifestyle characteristics relative to pollution exposure such as time spent outside and residence history. A pulmonary function feasibility study was done on a subsample of 86 women 50-64 years of age …

Sources Of Nosocomial Infections In Immunocompromised Patients (Letter), B. Burt Gerstman

Faculty Publications

No abstract provided.

Sero-Epidemiology Of Q Fever With Special Reference To Complications In A Hospital Population Of Southern California, Ajit Singh Randhawa

Loma Linda University Electronic Theses, Dissertations & Projects

[Abstract Not Included]