Curved Chaotic Map Time Series Models and Their Stochastic Reversals

This paper considers two types of chaotic map time series models, including the well-known tent, logistic and binary-shift maps as special cases; these are called curved tent and curved binary families. Deterministic behaviour is investigated by invariant distributions, Lyapunov exponents, and by serial dependency. Stochastic time reversal of the families is shown to produce models which have a broader range of stochastic and chaotic properties than their deterministic counterparts. The marginal distributions may have concentrations and restricted supports and are shown to be a non-standard class of invariant distribution. Dependenc y is generally weaker with the reversed stochastic models. The work gives a broad statistical account of deterministic and stochastically reversed map models, such as are emerging in random number generation, communica tion systems and cryptography     

The majority legal status of women in southern Africa: implications for women and families

Women in many countries of southern Africa do not have majority status or have only recently gained this right. Majority status grants individuals adult legal status and the right to bring matters to court, own and administer property, have legal custody of children, and contract for marriage. This article summarizes the legal status of women in Botswana, Lesotho, South Africa, Swaziland, Zambia, and Zimbabwe. Lack of majority status contributes to the ongoing risk of poverty for women and makes them overly dependent on men. Compounding the situation in these countries is the presence of a dual legal system. Improving the situation of women and their families involves targeting changes in the legal system, influencing implementation of laws, educating women about their rights, and giving women needed support to seek their legal rights. The legal status of women must be viewed in the context of historical changes in the economic, educational, political, and cultural developments of society.The research for this paper was conducted during her previous faculty affiliation with the University of Michigan, School of Social Work. Her research interests include the impact of social change on women and families, rural mental health services, and health and mental health linkages. She received her Ph.D. from Rutgers University and her M.S.W. from the Columbia University School of Social Work.Her research interests are gender, work and family, culture and power, social transformations in rural and peri-urban communities, critical education, women and community politics, history of women, family and kinship issues, and community-based program development and evaluation. She received her M.S.W. from Dalhousie University, Halifax.     

Statistics in epidemiology: the case-control study

This article presents a general review of the major trends in the conceptualization, development, and success of case-control methods for the study of disease causation and prevention. "Recent work on nested case-control, case-cohort, and two-stage case control designs demonstrates the continuing impact of statistical thinking on epidemiology. The influence of R. A. Fisher's work on these developments is mentioned wherever possible. His objections to the drawing of causal conclusions from observational data on cigarette smoking and lung cancer are used to introduce the problems of measurement error and confounding bias."     

Marketing and the medical specialist in the managed care environment

Marketing means more than just communicating or advertising to potential patients; marketing means identifying your customers and working to meet or exceed their expectations. There are five key areas of a marketing plan: (1) Establish the foundation, beginning with your mission statement; (2) Assess your marketing environment by internal and external research; (3) Target your efforts, looking at image and perception; (4) Develop your particular mix of product, price, place of distribution, and promotion; and (5) implement and evaluate your marketing process. This article discusses the importance of a marketing plan for the medical specialist and highlights the features unique to a practice working in a system of capitated reimbursement. Applying these principles will help to demonstrate added value, protect the fundamental role of the patient-physician relationship, ensure that our efforts are aligned with professional missions and goals, and ultimately increase profitability and professional success.     

Prevalence of gambling among Minnesota public school students in 1992 and 1995

The purposes of this study were to examine the prevalence of gambling among youth, compare rates of gambling between 1992 and 1995, and determine what levels of gambling frequency may be considered common and uncommon. The two samples included 122,700 Minnesota public school students in the 6th, 9th, and 12th grades in 1992; and 75,900 9th and 12th grade students in 1995. Students were administered the Minnesota Student Survey, a 126-item, anonymous, self-administered, paper-and-pencil questionnaire that inquires about multiple content domains, including gambling behaviors. The same questionnaire, with minor revisions to the gambling items, was administered in both 1992 and 1995 to students in their classrooms by the Minnesota Department of Education. There were slight decreases in overall gambling rates from 1992 to 1995. The majority of students gambled at least once during the past year. However, most did not play any game on a weekly/daily rate and did not report any problems associated with their gambling. Gender, grade, and race effects were found for gambling frequency. Boys gambled more often than girls, and 9th and 12th grade students gambled more often than 6th grade students. Asian American and White students reported lower rates of gambling frequency than Mexican/Latin American, African American, and American Indian students. From a statistical standpoint (i.e., beyond the 97.7 percentile), it may be considered in the uncommon range for girls to play two or more games at a weekly/daily rate, and for boys to play four or more games at a weekly/daily rate. Variables associated with gambling frequency included antisocial behavior, gender, and alcohol use frequency. Although the finding that gambling did not increase from 1992 to 1995 is encouraging, this is the first generation of youth to be exposed to widespread accessability to gambling venues and gambling advertising and it will be important to continue monitoring the prevalence of youth gambling.     

Marriage selection and age patterns of mortality: a mathematical investigation

"In this paper, we use simulation models to demonstrate the complexity of the relationship between the marriage selection process and the resulting RMRs [relative mortality ratios]. In particular, we show that marriage selection alone can produce a relative mortality ratio which remains large and relatively constant at ages far beyond the marriage span....Our general objective...is to determine the range of age patterns of relative mortality which could, in theory, result from marriage selection on the basis of health characteristics. We also evaluate the effects of variations in the marriage selection mechanisms on the resulting mortality patterns....We develop and apply several simple mathematical models of the marriage selection process. In order to distinguish the potential consequences of marriage selection from marriage protection, we consider hypothetical populations in which causal effects are absent....We begin by considering an extremely simple marriage selection process and subsequently explore a more realistic selection model based on recent death and marriage rates for Japan."     

Genetic screening technology: ethical issues in access to tests by employers and health insurance committees

Whereas the introduction of new technologies previously has raised the ethical question of who ought to have access to a new procedure or device, genetic testing technology raises the new ethical question of to whom access to a new technology ought to be limited. In this article we discuss the implications of employers and private health insurance companies having access to genetic testing technology. Although there may be legitimate business interests in allowing employers and insurers to conduct genetic screening, there are other valid societal interests in regulating or limiting the use of this technology by third parties. Public policy developed in the area of new genetic technology must reflect such interests.     

Subsidized elderly housing: public-private partnerships on the brink

Starting in the early 1960s, the federal government joined with the private-sector housing developers in a partnership: in return for subsidized mortgages and tax benefits, developers would rent to low- and moderate-income tenants. Today, many elderly people live in these "publicly subsidized" units. The initial agreement, however, held out an escape clause: after 15 to 20 years, for-profit developers that wanted to end the partnership could prepay their mortgages, leaving tenants in those buildings "at risk" of rent increases and/or evictions. This article discusses that partnership, its options for dissolution, and the current solutions to the problem of the expiring agreements, including a moratorium, vouchers, and incentives. The compromise legislation responds to all interested parties--owners, current and would-be tenants, local governments, tax-payers--through a multi-stage sequence of dissolution, yet such a finely tuned, acutely sensitive legislative solution may not work easily or efficiently.