Biomedical subjects

G D Williamson

Publications and source records attributed to G D Williamson.

At least 19 recordsLinked to original sources

PubMed2006

Statistics and public health at CDC.

Since CDC's inception, an important function of the agency has been the compilation, analysis, and interpretation of statistical information to guide actions and policies to improve health. Sources of data include vital statistics records, medical records, personal interviews, telephone and mail surveys, physical examinations, and laboratory testing. Public health surveillance data have been used to characterize the magnitude and distribution of illness and injury; to track health trends; and to develop standard curves, such as growth charts. Beyond the development of appropriate program study designs and analytic methodologies, statisticians have played roles in the development of public health data-collection systems and software to analyze collected data. CDC/ATSDR employs approximately 330 mathematical and health statisticians. They work in each of the four coordinating centers, two coordinating offices, and the National Institute for Occupational Safety and Health.

Centers for Disease Control and Prevention, U.S.↗

PubMed2001

Dynamic linear model and SARIMA: a comparison of their forecasting performance in epidemiology.

One goal of a public health surveillance system is to provide a reliable forecast of epidemiological time series. This paper describes a study that used data collected through a national public health surveillance system in the United States to evaluate and compare the performances of a seasonal autoregressive integrated moving average (SARIMA) and a dynamic linear model (DLM) for estimating case occurrence of two notifiable diseases. The comparison uses reported cases of malaria and hepatitis A from January 1980 to June 1995 for the United States. The residuals for both predictor models show that they were adequate tools for use in epidemiological surveillance. Qualitative aspects were considered for both models to improve the comparison of their usefulness in public health. Our comparison found that the two forecasting modelling techniques (SARIMA and DLM) are comparable when long historical data are available (at least 52 reporting periods). However, the DLM approach has some advantages, such as being more easily applied to different types of time series and not requiring a new cycle of identification and modelling when new data become available.

Communicable Disease Control↗

PubMed2000

Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group.

OBJECTIVE: Because of the pressure for timely, informed decisions in public health and clinical practice and the explosion of information in the scientific literature, research results must be synthesized. Meta-analyses are increasingly used to address this problem, and they often evaluate observational studies. A workshop was held in Atlanta, Ga, in April 1997, to examine the reporting of meta-analyses of observational studies and to make recommendations to aid authors, reviewers, editors, and readers. PARTICIPANTS: Twenty-seven participants were selected by a steering committee, based on expertise in clinical practice, trials, statistics, epidemiology, social sciences, and biomedical editing. Deliberations of the workshop were open to other interested scientists. Funding for this activity was provided by the Centers for Disease Control and Prevention. EVIDENCE: We conducted a systematic review of the published literature on the conduct and reporting of meta-analyses in observational studies using MEDLINE, Educational Research Information Center (ERIC), PsycLIT, and the Current Index to Statistics. We also examined reference lists of the 32 studies retrieved and contacted experts in the field. Participants were assigned to small-group discussions on the subjects of bias, searching and abstracting, heterogeneity, study categorization, and statistical methods. CONSENSUS PROCESS: From the material presented at the workshop, the authors developed a checklist summarizing recommendations for reporting meta-analyses of observational studies. The checklist and supporting evidence were circulated to all conference attendees and additional experts. All suggestions for revisions were addressed. CONCLUSIONS: The proposed checklist contains specifications for reporting of meta-analyses of observational studies in epidemiology, including background, search strategy, methods, results, discussion, and conclusion. Use of the checklist should improve the usefulness of meta-analyses for authors, reviewers, editors, readers, and decision makers. An evaluation plan is suggested and research areas are explored.

Epidemiology↗

PubMed2000

Facilitating use of analytic methods at a federal agency.

Identification and application of appropriate analytic methods are critical pieces of the foundation of science. Because of the increasingly complex issues federal agencies face and the increasing importance of addressing those issues with multi-disciplinary teams that offer knowledge and skills in many methods areas, it is important that agencies foster coordinated integration of analytic methods. This report discusses the Centers for Disease Control and Prevention's (CDC's) evolving needs regarding analytic methods and includes activities that CDC has undertaken to facilitate a coordinated approach to the use of the statistical sciences. We introduce a new framework for facilitating coordination in analytic methods as a hybrid model, blending attributes of centralized and decentralized resource models. This coordinating focus approach offers assets of timeliness, efficiency, and effectiveness, as well as fosters strengthened relationships among scientists and increased collaboration among scientific disciplines.

Centers for Disease Control and Prevention, U.S.↗

PubMed1999

A monitoring system for detecting aberrations in public health surveillance reports.

Routine analysis of public health surveillance data to detect departures from historical patterns of disease frequency is required to enable timely public health responses to decrease unnecessary morbidity and mortality. We describe a monitoring system incorporating statistical 'flags' identifying unusually large increases (or decreases) in disease reports compared to the number of cases expected. The two-stage monitoring system consists of univariate Box-Jenkins models and subsequent tracking signals from several statistical process control charts. The analyses are illustrated on 1980-1995 national notifiable disease data reported weekly to the Centers for Disease Control and Prevention (CDC) by state health departments and published in CDC's Morbidity and Mortality Weekly Report. Published in 1999 by John Wiley & Sons, Ltd. This article is a U.S. Government work and is in the public domain in the United States.

Centers for Disease Control and Prevention, U.S.↗

PubMed1999

A study of the average run length characteristics of the National Notifiable Diseases Surveillance System.

This study examines the statistical properties (that is, false positive and negative signals) in detecting unusual patterns of reported cases of diseases from the Centers for Disease Control and Prevention's National Notifiable Diseases Surveillance System. Control charts are applied to the residuals of one-step ahead forecasts based on Box-Jenkins models of reported cases of disease. Simulation and analytical techniques are used to study the average run length characteristics of these control charts for various types of changes in the levels of the series, including spike, trend and step changes. The average run lengths for the highly correlated disease series are much longer than for the usual independent data case. This increase in the average run lengths is strongly influenced by the type of change in the level of the series and by the type of control chart. Understanding the average run length characteristics of the control charts can lead to timely detection of changes in the levels of disease series, and subsequent timely public health actions to decrease unnecessary morbidity and mortality.

Centers for Disease Control and Prevention, U.S.↗

PubMed1999

Spatial and temporal patterns in final amendments to provisional disease counts.

This article examines temporal and spatial patterns in the relationship between provisional and amended reports for Hepatitis A and Hepatitis B received from each state by the Centers for Disease Control and Prevention through the U.S. National Notifiable Diseases Surveillance System from 1980 to 1992. It demonstrates that, as the 1980s unfolded, the preliminary disease reports became less representative markers of final disease counts. Practitioners at the state and community levels need to be aware of the temporal and spatial instabilities in such provisional data if they are used to provide early warning of contemporary health aberrations.

Centers for Disease Control and Prevention, U.S.↗

PubMed1997

Comparison of effect estimates from a meta-analysis of summary data from published studies and from a meta-analysis using individual patient data for ovarian cancer studies.

To determine the relative merits of two quantitative methods used to estimate the summary effects of observational studies, the authors compared two methods of meta-analysis. Each quantified the relation between oral contraceptive use and the risk for ovarian cancer. One analysis consisted of a meta-analysis using summary data from 11 published studies from the literature (MAL) in which the study was the unit of analysis, and the second consisted of a meta-analysis using individual patient data (MAP) in which the patient was the unit of analysis. The authors found excellent quantitative agreement between the summary effect estimates from the MAL and the MAP. The MAP permits analysis 1) among outcomes, exposures, and confounders not investigated in the original studies, 2) when the original effect measures differ among studies and cannot be converted to a common measure (e.g., slopes vs. correlation coefficients), and 3) when there is a paucity of studies. The MAL permits analysis 1) when resources are limited, 2) when time is limited, and 3) when original study data are not available or are available only from a biased sample of studies. In public health epidemiology, data from original studies are often accessible only to limited numbers of research groups and for only a few types of studies that have high public health priority. Consequently, few opportunities for pooled analysis exist. However, from a policy view, MAL will provide answers to many questions and will help in identifying questions for future investigation.

Bias↗

PubMed1997

The importance of long-term records in public health surveillance: the US weekly sanitary reports, 1888-1912, revisited.

BACKGROUND: This paper outlines the ways in which a little-used archive of early public health records may throw light on longer-term trends in international epidemic behaviour and serve as a major source of epidemiological information for historians of urbanization and public health. The Weekly Abstract of Sanitary Reports was the official disease surveillance report of the US Public Health Service and its predecessors, and began to publish urban mortality statistics on a regular basis in 1888. Here, the authors describe the first 25 years of continuous reporting (1888-1912), when the Reports contained not only disease data for US cities, but also records sent back by US consuls based in some 250 cities in many parts of the world. METHODS: The content of the weekly editions of the Reports was systematically sampled and analysed using graphical techniques and the simple statistical method of running means. RESULTS: Relatively complete weekly series of mortality from all causes, and six infectious diseases (diphtheria, enteric or typhoid fever, measles, scarlet fever, tuberculosis and whooping cough) were identified for a total of 100 cities world-wide. CONCLUSION: Reporting coverage for these cities is sufficiently complete that multivariate analysis should be possible to obtain a comparative picture of mortality for many parts of the world. Despite limitations of the data, sources of the type described in this paper form an important comparative database for studying international patterns of mortality.

Communicable Diseases↗

PubMed1997

A method for timely assessment of influenza-associated mortality in the United States.

Influenza-associated mortality has traditionally been estimated as the excess mortality above a baseline of deaths during influenza epidemic periods. Excess mortality estimates are not timely, because national vital statistics data become available after a period of 2-3 years. To develop a method for timely reporting, we used the 121 Cities Surveillance System (121 Cities), maintained at the Centers for Disease Control and Prevention, as an alternative data source. We fit a cyclical regression model to time series of weekly 121 Cities pneumonia and influenza deaths for 1972-1996 to estimate the excess pneumonia and influenza mortality and to compare these figures with national vital statistics estimates for 20 influenza seasons during 1972-1992. Seasonal excess mortality based on 121 Cities correlated well with the national data: for 18 (90%) of 20 seasons, our influenza epidemic severity index category approximated the result based on national vital statistics. We generated preliminary severity categories for the four recent seasons during 1992-1996. We conclude that the 121 Cities Surveillance System can be used for the timely assessment of the severity of future influenza epidemics and pandemics. Timely pneumonia and influenza mortality reporting systems established in sentinel countries worldwide would help alert public health officials and allow prompt prevention and intervention strategies during future influenza epidemics and pandemics.

Centers for Disease Control and Prevention, U.S.↗

PubMed1997

The impact of influenza epidemics on mortality: introducing a severity index.

OBJECTIVES: The purpose of this study was to assess the impact of recent influenza epidemics on mortality in the United States and to develop an index for comparing the severity of individual epidemics. METHODS: A cyclical regression model was applied to weekly national vital statistics from 1972 through 1992 to estimate excesses in pneumonia and influenza mortality and all-cause mortality for each influenza season. Each season was categorized on the basis of increments of 2000 pneumonia and influenza excess deaths, and each of these severity categories was correlated with a range of all-cause excess mortality. RESULTS: Each of the 20 influenza seasons studied was associated with an average of 5600 pneumonia and influenza excess deaths (range, 0-11,800) and 21,300 all-cause excess deaths (range, 0-47,200). Most influenza A(H3N2) seasons fell into severity categories 4 to 6 (23,000-45,000 all-cause excess deaths), whereas most A(H1N1) and B seasons were ranked in categories 1 to 3 (0-23,000 such deaths). CONCLUSIONS: From 1972 through 1992, influenza epidemics accounted for a total of 426,000 deaths in the United States, many times more than those associated with recent pandemics. The influenza epidemic severity index was useful for categorizing severity and provided improved seasonal estimates of the total number of influenza-related deaths.

Cause of Death↗

PubMed1995

Photochemistry of type I acid-soluble calf skin collagen: dependence on excitation wavelength.

Although previous studies have demonstrated that the predominant photochemistry of type I collagen under 254 nm irradiation may be attributed either to direct absorption by tyrosine/phenylalanine or to peptide bonds, direct collagen photochemistry via solar UV wavelengths is much more likely to involve several age- and tissue-related photolabile collagen fluorophores that absorb in the latter region. In this study, we compare and contrast results obtained from irradiation of a commercial preparation of acid-soluble calf skin type I collagen in solution with UVC (primarily 254 nm), UVA (335-400 nm) and broad-band solar-simulating radiation (SSR; 290-400 nm). Excitation spectroscopy and analysis of photochemically induced disappearance of fluorescence (fluorescence fading) indicates that this preparation has at least four photolabile fluorescent chromophores. In addition to tyrosine and L-3,4-dihydroxyphenylalanine, our sample contains two other fluorophores. Chromophore I, with emission maximum at 360 nm, appears to be derived from interacting aromatic moieties in close mutual proximity. Chromophore II, with broad emission at 430-435 nm, may be composed of one or more age-related molecules. Collagen fluorescence fading kinetics are sensitive to excitation wavelength and to conformation. Under UVC, chromophore I fluorescence disappears with second-order kinetics, indicating a reaction between two proximal like molecules. Adherence to second-order kinetics is abrogated by prior denaturation of the collagen sample. A new broad, weak fluorescence band at 400-420 nm, attributable to dityrosine, forms under UVC, but not under solar radiation. This band is photolabile to UVA and UVB wavelengths.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The application of multidimensional scaling methods to epidemiological data.

This paper illustrates the use of multidimensional scaling methods (MDS) to examine space-time patterns in epidemic data. The paper begins by outlining the principles of MDS. The model is then formally specified and illustrated by application to two data sets. The first is partly a tutorial example. It uses monthly reported measles morbidity data for the 31-year period from January 1960 to December 1990, collected for the 50 states of the USA, plus New York City and the District of Columbia. These data are used to explore the various ways in which MDS may be used to identify changing spatial patterns in geographically-coded data. In addition to their tutorial use, the data are also employed to search for any substantive changes in the geographical structure of measles epidemics in the USA that may have followed the introduction of mass vaccination in 1965. New England appears to have developed an epidemic profile distinct from the rest of the USA, and there is tentative evidence of an urban-rural split in epidemic characteristics. The second data set takes annual reported measles mortality data for New Zealand and the states of Australia from 1860 to 1949. MDS is used to show how the spatial relationships among these geographical units have changed over time in response to changes in the sizes of local susceptible populations.

Australia↗

PubMed1994

Models for three-dimensional contingency tables with completely and partially cross-classified data.

We develop models for three-dimensional contingency tables containing both completely and partially cross-classified data for which one of the variables is regarded as dependent and the other two variables are regarded as independent variables. Parameters of interest include the cell probabilities and the probabilities that the observations on one or both independent variables are missing. The models allow inferences on these two sets of probabilities to be made independently. Maximum likelihood methods for estimating and testing hypotheses regarding these parameters are described, along with conditional goodness-of-fit test statistics, which display a convenient additivity property. The methodology is applied to cervical cancer data from a case-control study performed in Atlanta, Georgia, 1985-1988.

Adult↗

PubMed1993

Mammography use and outcomes in a community. The Greater Lansing Area Mammography Study.

BACKGROUND: Mammography is widely known to reduce morbidity and mortality from breast cancer, but a population-based assessment of mammography use and follow-up of mammography findings has not been reported previously. METHODS: An observational, population-based, follow-up study was conducted of all women having mammograms in the Greater Lansing, Michigan, metropolitan area, between June 1987 and June 1988. A total of 17,811 Greater Lansing women participated. The adherence of women to mammography screening guidelines was estimated, and mammography's utility to detect breast cancer was assessed through follow-up review of breast biopsy results. RESULTS: Thirty-seven percent of the expected number of women 35 years of age and older had mammograms. Adherence to screening guidelines declined with age, and less than 5% (302 of 6700) of women 55 years of age and older reporting having annual mammograms. Seventy-six percent of women reported that their physicians prompted the examination. The predictive value of a positive mammogram was 21.9% for women without symptoms and 32.4% for women with symptoms. Mammography's sensitivity and specificity for breast cancer detection were 71% and 98%, respectively. CONCLUSIONS: The study highlights the need to target mammography to women 50 years of age and older, underscores the importance of physicians in promoting mammography, and demonstrates the analytic value and limitation of mammography in clinical decision-making.

Adult↗

PubMed1991

The diagnosis of ovarian cancer by pathologists: how often do diagnoses by contributing pathologists agree with a panel of gynecologic pathologists?

The Cancer and Steroid Hormone Study, a multicenter, population-based, case-control study of ovarian, breast, and endometrial cancer in women 20 to 54 years of age, permitted the diagnoses of contributing pathologists to be compared with those of a panel of three gynecologic pathologists. A diagnosis of ovarian cancer was made by contributing pathologists on 477 subjects. Agreement between the two groups of pathologists was 97% for primary epithelial ovarian cancer and 89% for primary nonepithelial ovarian malignancies. Agreement on diagnosis of major cellular subtypes of ovarian malignancy ranged between 73% for endometrioid cancer and 100% for clear cell carcinomas. We conclude that the diagnosis of pathologic features of primary ovarian cancer is highly predictable. Nonetheless, diagnosis by histologic type varies sufficiently that a review process should be considered for clinical or investigative decisions involving specific histologic diagnoses of ovarian cancer.

Adult↗

PubMed1989

Detection of aberrations in the occurrence of notifiable diseases surveillance data.

The detection of unusual patterns in the occurrence of diseases and other health events presents an important challenge to public health surveillance. This paper discusses three analytic methods for identifying aberrations in underlying distributions. The methods are illustrated on selected infectious diseases included in the National Notifiable Diseases Surveillance System of the Centers for Disease Control. Results suggest the utility of such an analytic approach. Further work will determine the sensitivity of such methods to variations in the occurrence of disease. These methods are useful for evaluating and monitoring public health surveillance data.

Centers for Disease Control and Prevention, U.S.↗

PubMed1988

Ventricular rhythm with intermediate rate in the neonate without heart disease.

Nonsustained, sustained, or incessant AVR, a form of VRIR, although infrequent, can present in the neonatal period. It must be considered in the differential diagnosis of wide QRS tachycardia. It seems to be different from VI, and it is asymptomatic and self-limited. It has good long-term prognosis and requires no treatment. These patients should not undergo invasive diagnostic evaluation unless symptoms develop.

Electrocardiography↗