Clinical Epidemiology Commons^™

Is The Number Of Sick Persons In A Cohort Constant Over Time?, Paula Diehr, Ann Derleth, Anne Newman, Liming Cai

UW Biostatistics Working Paper Series

Objectives: To estimate the number of persons in a cohort who are sick, over time.

Methods: We calculated the number of sick persons in the Cardiovascular Health Study (CHS), a cohort study of older adults followed up to 14 years, using eight definitions of “healthy” and “sick”. We projected the number in each health state over time for a birth cohort.

Results: The number of sick persons in CHS was approximately constant for 14 years, for all definitions of “sick”. The estimated number of sick persons in the birth cohort was approximately constant from ages 55-75, after which it decreased. …

Secular Trends In Life Expectancy By Diet Status Among Never Smoking Seventh-Day Adventists, Noha Salim Daher

Loma Linda University Electronic Theses, Dissertations & Projects

To evaluate how life expectancy changed by age and secular time from 1960 through 1988, two cohort studies, the Adventist Mortality Study (AMS, 1960-1985, n = 27,530) and the Adventist Health Study (AHS, 1976-1988, n = 34,192) were combined. The life expectancy of omnivores was compared to vegetarians separately in never-smoking males and females for all-cause mortality, and where the cause of death was cardiovascular disease or all site-cancer. Life expectancies were calculated for subjects who had survived to ages 30, 50, 70, and 80 during six calendar periods: 1960- 1964, 1965-1969, 1970-1974, 1975-1979, 1980-1984, and 1985-1988. Ten-year calendar periods …

Evaluation Of Over-The-Counter Sales As A Syndromic Surveillance Method For Waterborne Disease In New Mexico, Camilla M. Bustamante

Health, Exercise, and Sports Sciences ETDs

This research evaluates the use of Over-the-Counter anti-diarrheal medications as a potential syndromic indicator and surveillance mechanism for waterborne disease in New Mexico. The purpose was to determine the usefulness of such data for either supplemental or stand alone use in a system for waterborne disease surveillance. The use of syndromic indicators for waterborne disease was elevated in 1993 after an outbreak of cryptosporidium was detected in Milwaukee Wisconsin by an alert pharmacist who noticed increased sales of over-the-counter medications over a period of time. In 2001, terrorist threats for anthrax exposure to U.S. populations further prompted funding and research …

Insights Into Latent Class Analysis, Margaret S. Pepe, Holly Janes

UW Biostatistics Working Paper Series

Latent class analysis is a popular statistical technique for estimating disease prevalence and test sensitivity and specificity. It is used when a gold standard assessment of disease is not available but results of multiple imperfect tests are. We derive analytic expressions for the parameter estimates in terms of the raw data, under the conditional independence assumption. These expressions indicate explicitly how observed two- and three-way associations between test results are used to infer disease prevalence and test operating characteristics. Although reasonable if the conditional independence model holds, the estimators have no basis when it fails. We therefore caution against using …

Standardizing Markers To Evaluate And Compare Their Performances, Margaret S. Pepe, Gary M. Longton

UW Biostatistics Working Paper Series

Introduction: Markers that purport to distinguish subjects with a condition from those without a condition must be evaluated rigorously for their classification accuracy. A single approach to statistically evaluating and comparing markers is not yet established.

Methods: We suggest a standardization that uses the marker distribution in unaffected subjects as a reference. For an affected subject with marker value Y, the standardized placement value is the proportion of unaffected subjects with marker values that exceed Y.

Results: We apply the standardization to two illustrative datasets. In patients with pancreatic cancer placement values calculated for the CA 19-9 marker are smaller …

Combining Predictors For Classification Using The Area Under The Roc Curve, Margaret S. Pepe, Tianxi Cai, Zheng Zhang, Gary M. Longton

UW Biostatistics Working Paper Series

No single biomarker for cancer is considered adequately sensitive and specific for cancer screening. It is expected that the results of multiple markers will need to be combined in order to yield adequately accurate classification. Typically the objective function that is optimized for combining markers is the likelihood function. In this paper we consider an alternative objective function -- the area under the empirical receiver operating characteristic curve (AUC). We note that it yields consistent estimates of parameters in a generalized linear model for the risk score but does not require specifying the link function. Like logistic regression it yields …

Ukimwi : Hiv/Aids In Kenya, Virginia Wangui Gathua

Graduate Research Papers

This manuscript points out the deficiencies school counseling programs in Kenya for children/adolescents affected/infected by HIV/AIDS. In addition, the paper is intended to inform, guide, and encourage policy makers, program developers, and school counselors as they develop school counseling interventions for the disease. The focus of the paper is limited to children/adolescents because they bear the greatest burden of HIV/ AIDS infections. The paper also provides evidence for planning and implementation of culturally and developmentally relevant, school-based counseling interventions. The paper explores the impact of HIV/AIDS on Kenyan children/adolescents infected/affected by HIV/AIDS and points out the factors that hinder prevention …