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A model of unlinked diallelic loci affecting the risk of a complex inherited disease is explored. The loci are equivalent in their effect on disease risk and are in Hardy--Weinberg and linkage equilibrium. The goal is to determine what assumptions about dependence of disease risk on genotype are consistent with data for diseases such as schizophrenia, bipolar disorder, autism, and multiple sclerosis that are relatively common (0.1-2% prevalence) and that have high concordance rates for monozygotic twins (30-50%) and high risks to first-degree relatives of affected individuals (risk ratios exceeding 4). These observations are consistent with a variety of models, including generalized additive, muhiplicative, and threshold models, provided that disease risk increases rapidly for a narrow range of numbers of causative alleles. If causative alleles are in relatively high frequency, then the combined effects of numerous causative loci are necessary to substantially elevate disease risk.

Objective To investigate and compare seven types of injection devices for their risks of iatrogenic transmission of bloodborne pathogens and their economic costs in sub-Saharan Africa. Methods Risk assumptions for each device and cost models were constructed to estimate the number of new hepatitis B virus (HBV) and human immunodeficiency virus (HIV) infections resulting from patient-to-patient, patient-to-health care worker, and patient-to-community transmission. Costs of device purchase and usage were derived from the literature, while costs of direct medical care and lost productivity from HBV and HIV disease were based on data collected in 1999 in Cote d'Ivoire, Ghana, and Uganda. Multivariate sensitivity analyses using Monte Carlo simulation characterized uncertainties in model parameters. Costs were summed from both the societal and health care system payer's perspectives. Findings Resterilizable and disposable needles and syringes had the highest overall costs for device purchase, usage, and iatrogenic disease: median US$ 26.77 and US$ 25.29, respectively, per injection from the societal perspective. Disposable-cartridge jet injectors and automatic needle-shielding syringes had the lowest costs, US$ 0.36 and US$ 0.80, respectively. Reusable-nozzle jet injectors and auto-disable needle and syringes were intermediate, at USS 0.80 and USS 0.91, respectively, per injection. Conclusion Despite their nominal purchase and usage costs, conventional needles and syringes carry a hidden but huge burden of iatrogenic disease. Alternative injection devices for the millions of injections administered annually in sub-Saharan Africa would be of value and should be considered by policy-makers in procurement decisions. Keywords Disease transmission; Iatrogenic disease/epidemiology; Injections/instrumentation/economics; Needles/adverse effects/ economics; Syringes/adverse effects/economics; Injections, Jet; Hepatitis B/transmission; HIV infections/transmission; Risk factors; Costs and cost analysis; Models, Theoretical; Africa South of the Sahara (source: MeSH, NLM). Mots cles Transmission maladie; Affection iatrogenique/epidemiologie; Injections/instrumentation/economie; Aiguille/effets indesirables/economie; Injections flash; Seringue/effets indesirables/economie; Hepatite B/transmission; HIV, Infection/transmission; Facteur risque; Cout et analyse cout; Modele theorique; Afrique subsaharienne (source: MeSH, INSERM). Palabras clave Transmision de enfermedad; Enfermedad iatrogenica/epidemiologia; Inyecciones/instrumentacion/economia; Agujas/efectos adversos/economia; Jeringas/efectos adversos/economia; Inyecciones a chorro; Hepatitis B/transmision; Infecciones por VIH/transmision; Factores de riesgo; Costos y analisis de costo; Modelos teoricos; Africa al Sur del Sahara (fuente: DeCS, BIREME). Bulletin of the World Health Organization 2002;80:859-870. Voir page 867 le resume en francais. En la pagina 867 figura un resumen en espanol., Introduction The Expanded Programme on Immunization has been increasingly successful in reducing the incidence of vaccine-preventable diseases in developing countries (1), where, unfortunately, a pattern of unsafe injection practices has [...]

This paper addresses the issues surrounding an individual's exposure to potential environmental risk factors, which can be implicated in the aetiology of a disease. We hope to further elucidate the 'lag' or latency period between the initial exposure to potential pathogens and the physical emergence of the disease, with specific reference to the rare neurological condition, motor neurone disease (MND), using a dataset obtained from the Finnish Death Certificate registry, for MND deaths between the period 1985-1995. A space-time approach is adopted, whereby patterns in both time and space are considered. No prior assumptions about the aetiology of MND are adopted. By using methods for the analysis of point processes, which preserve the continuous nature of the data, we resolve some of the problems of analysis that are often based on arbitrary areal units, such as postcode boundaries, or political boundaries. We use kernel estimation to model space-time patterns. Raised relative risk is assessed by adopting appropriate adjustments for the underlying population at risk, with the use of controls. Significance of the results is assessed using Monte Carlo simulation, and comparisons are made with results obtained from Openshaw's geographical analysis machine (GAM). Our results demonstrate the utility of kernel estimation as a visualisation tool. Small areas of elevated risk are identified, which need to be more closely examined before any firm conclusions can be drawn. We highlight a number of issues concerning the inadequacies of the data, and possibly of the techniques themselves.

A framework for analyzing the impact of cancer risk factors is developed and applied to a case-control study of melanoma. It is shown that the standardized incidence ratio of second primaries can be used to estimate the total coefficient of variation in risk in the population. This coefficient of variation can then serve as a benchmark for assessing the contributions of individual known risk factors to the total., 1. INTRODUCTION Over the past several decades, countless case-control and cohort studies have been conducted with the goal of identifying risk factors for cancer and quantifying the degrees of risk [...]

As social change and economic development have proceeded, the prevalence of chronic diseases, especially cardiovascular diseases, has increased in the developing world. In part this is due to the adoption of diets and other health behaviors characteristic of industrialized nations; in part it is a function of changing social and economic circumstances. In this paper, we describe the development and testing of a model designed to account for social and economic effects on cardiovascular disease risk. The model incorporates the fact that global economic processes have made a lifestyle characterized by the consumption of Euroamerican material goods and information a basis for the assignment of social status in local communities. But economic change at the local level is rarely sufficient to provide a foundation for individuals' status aspirations. Hence, many individuals attempt to maintain a lifestyle inconsistent with their economic standing, a variable we term lifestyle incongruity. Here we describe how this factor is associated with higher blood pressure in a variety of settings and also how the effects of lifestyle incongruity can be modified in local contexts by social class and social role processes. This latter process, contextual modification, is illustrated by data from American Samoa. In this example, the association of lifestyle incongruity with blood pressure is examined in 30 male household heads and 26 spouses. After an examination of Samoan ethnography focused attention on the importance of age and gender differences as defining social contexts of intracultural variation, the model was modified to assess interactions between age and gender as they affect the association of lifestyle incongruity and blood pressure. Lifestyle incongruity is strongly associated with higher systolic and diastolic blood pressure for the younger household heads, minimally associated with blood pressure for older household heads, and only slightly associated with the blood pressure of their spouses. The regression coefficients for the lifestyle incongruity by age by sex interaction term was significant at P [less than or equal to] 0.01 for both systolic and diastolic blood pressure. The consistency of these results with expectations based on the ethnographic record is emphasized in the interpretation. We feel that the lifestyle incongruity model represents an empirically successful attempt to link global political-economic processes, local social structure, and biological outcomes. Am J Phys Anthropol 102:55-66, 1997. KEY WORDS social status; blood pressure; social context

THE STAGES OF BEHAVIOR CHANGE MODEL has been used to understand a variety of health behaviors. Since consistent condom use has been promoted as a risk-reduction behavior for prevention of […]

A statistical-based methodology is developed to describe sequential screening guidelines for risk measurement. The study is limited to stable risk factor assessments for individuals over the duration of the screening period. A risk function is established to indicate disease risk levels and optimal intervention and screening programs. The model can be applied to screen for high risk individuals and determine a suitable intervention program., 1. INTRODUCTION Many risk factors for diseases are continuous variables, which are subject to measurement error and vary within subjects over time. A single measurement of the factor may give [...]

Objectives. The spread of the human immunodeficiency virus (HIV) in the general population has been a much debated topic in the mass media. The aim of this study was to create an approach to estimating the risk of exposure to HIV resulting from sexual behaviors. Methods. A theoretical estimate was applied to data obtained from a large-scale risk factor survey carried out in Britain. An HIV infection-exposure risk index was constructed by ranking different sex-related categorizations derived from variables in the survey. Results. The risk index involved a Delphi-based assessment of self-reported behavioral factors associated with HIV exposure and subsequent transmission. Roughly 85% of the adult population aged 18 to 50 were estimated to be at some risk for behavioral exposure to HIV virus with regard to reported sexual behavior. Over time, those who could be considered at no risk have declined as a proportion of the population. Conclusions. The estimates appear to refute commonplace assertions that exposure to HIV through sexual behavior is not a problem for general populations., The relation between transmission of HIV infection and sexual behavior in the general population may be modeled as a diffusion process or as a risk analysis of sexual behavior. Longitudinal data from a health and life-style survey conducted in the UK annually from 1987 through 1992 were used to analyze the risk involved in different kinds of sexual behavior. An HIV infection-exposure risk index was devised by ranking different sex-related categories taken from variables in the survey. Among respondents aged 18 to 50, approximately 85% were found to be at some risk of exposure to the HIV virus on the basis of their sexual behavior. Only about 2% are at very high risk. Younger adults take part in riskier sexual behaviors than do older adults. The proportion of those in the population who could be considered at no risk has declined over time.

A clinical model based on the severity of illness of patients undergoing a coronary artery bypass operation may be better at predicting an outcome of death or complications than methods currently used. Patients who were older or who had a previous emergency procedure, high blood creatinine levels, severe dysfunction of the left ventricle of the heart, insufficiency in the mitral valve, a hematocrit of 0.34, chronic lung disease or previous vascular surgery were more likely to die after coronary artery bypass surgery than were other patients. Individuals with diabetes, a high body weight (65 kg or more), aortic stenosis or cerebrovascular disease also had a higher risk of death than other individuals. Mathematical equations waiting the different factors were developed to classify patients undergoing coronary artery bypass in different risk categories. Patients were assigned risk-factor values of one to six points, and those with more points had a higher risk of death or complications such as infection, kidney failure or the need for artificial assistance.

A study was conducted to analyze a novel methodology of modeling the second portion of two-part models for predicting medical risk. The approach utilizes extensions of a generalized linear framework. It also supports demographic variables and an Ambulatory Care Group variable to accommodate prior health status. In addition, the methodology allows the formal evaluation of the choice of link and variance functions.