On the incidence–prevalence relation and length‐biased sampling

For many diseases, logistic constraints render large incidence studies difficult to carry out. This becomes a drawback, particularly when a new study is needed each time the incidence rate is investigated in a new population. By carrying out a prevalent cohort study with follow‐up it is possible to estimate the incidence rate if it is constant. The authors derive the maximum likelihood estimator (MLE) of the overall incidence rate, λ, as well as age‐specific incidence rates, by exploiting the epidemiologic relationship, (prevalence odds) = (incidence rate) × (mean duration) (P/[1 ? P] = λ × µ). The authors establish the asymptotic distributions of the MLEs and provide approximate confidence intervals for the parameters. Moreover, the MLE of λ is asymptotically most efficient and is the natural estimator obtained by substituting the marginal maximum likelihood estimators for P and µ into P/[1 ? P] = λ × µ. Following‐up the subjects allows the authors to develop these widely applicable procedures. The authors apply their methods to data collected as part of the Canadian Study of Health and Ageing to estimate the incidence rate of dementia amongst elderly Canadians. The Canadian Journal of Statistics © 2009 Statistical Society of Canada     

Bayesian inference for dynamic social network data

We consider a continuous-time model for the evolution of social networks. A social network is here conceived as a (di-) graph on a set of vertices, representing actors, and the changes of interest are creation and disappearance over time of (arcs) edges in the graph. Hence we model a collection of random edge indicators that are not, in general, independent. We explicitly model the interdependencies between edge indicators that arise from interaction between social entities. A Markov chain is defined in terms of an embedded chain with holding times and transition probabilities. Data are observed at fixed points in time and hence we are not able to observe the embedded chain directly. Introducing a prior distribution for the parameters we may implement an MCMC algorithm for exploring the posterior distribution of the parameters by simulating the evolution of the embedded process between observations.     

The influence of sexual orientation on career decision-making: a research note

This study investigates differences between heterosexuals and homosexuals of both sexes with regard to several variables in the career decision-making process: anxiety about making a career choice, indecisiveness about the choice, need to acquire information about the career of choice, uncertainty about the choice, and career choice dissatisfaction. Significant interactions are found on choice uncertainty (gay men having the highest level of uncertainty and lesbian women the lowest) and choice dissatisfaction (heterosexual women and gay men showing more dissatisfaction than the other two groups).     

Residential and Racial Mortality Differentials in the South by Cause of Death1

Abstract Mortality levels and differences by metropolitan-nonmetropolitan residence for blacks and whites are examined in the South using life-table techniques. Life tables are constructed for Southern subpopulations using U.S. vital statistics and census data for 1980, and differences in the life expectancies are decomposed by cause of death. Results suggest that life expectancy is higher for metropolitan and white populations. Racial mortality differences are slightly greater in metropolitan areas of the South when compared to the nonmetropolitan South. Residential mortality differences are attributable mainly to differences in the effects of heart disease and accidents. Most of the racial mortality difference is due to differences in effects of malignant neoplasms, cardiovascular disease, perinatal conditions, and homicide. Policy efforts aimed at specific causes of death in specific populations are suggested as a means of reducing racial or residential life expectancy differentials.     

Children's time in structured and unstructured leisure activities

Using the 1981 Time Use Longitudinal Panel Study data, this study examines factors which influence children's time use in leisure activities. More time is spent in unstructured than structured leisure activities. Analysis of variance is performed on 32 categories of leisure time, including total leisure, to determine the influence of characteristics of the child and the mother and other socioeconomic characteristics. Males spend significantly more time than females in active sports, playing games, and passive leisure especially watching television on weekends. Females spend significantly more time than males socializing on weekends. The amount of time spent socializing increases with age but decreases with employment. Time spent playing games decreases with age, increases with number of children, and decreases as family income increases. Given the large number of children who do not participate in a given set of leisure activities, future research should examine the probability of participation.The data used in this article were made available by the Inter-university Consortium for Political and Social Research. The data for Time Use Longitudinal Panel Study, 1975–1981 were originally collected by F. Thomas Juster, Martha S. Hill, Frank P. Stafford, and Jacquelynne Eccles Parsons of the Survey Research Center, Institute for Social Research, The University of Michigan. Neither the collector of the original data nor the Consortium bear any responsibility for the analysis or interpretation presented here.Carol B. Meeks is a Professor and Teresa Mauldin is an Assistant Professor in the Department of Housing and Consumer Economics, The University of Georgia, Athens, GA 30602. Dr. Meeks' research interests include time use, family structure, and economic aspects of housing. She received her Ph.D. from Ohio State University. Dr. Mauldin, who also received her Ph.D. from Ohio State University, is interested in time use, economic well being of individuals and families, and family structure.     

Simulation model of a predator-prey system comprised ofPhytoseiulus persimilis andTetranychus urticae. II. Model sensitivity to variations in the life history parameters of both species and to variations in the functional response and components of the numerical response

Summary A detailed sensitivity analysis of a model of a predator-prey system comprised ofTetranychus urticae andPhytoseiulus persimilis was performed. The aim was to assess the relative importance of the life history parameters of both species, the functional response, and the components of the numerical response. In addition, the impact of the initial predator-prey ratio and the timing of predator introduction were tested. Results indicated that the most important factors in the system were relative rates of predator and prey development, the time of onset of predator oviposition, and the mode of the predator's oviposition curve. The total oviposition of the predator, the effect of prey consumption on predator oviposition, and predator searching were important under some conditions. Factors of moderate importance were the adult female predator's functional response, total prey oviposition, the mode of the prey's oviposition curve, abiotic mortality of the pre-adult predator, and the effect of prey consumption on predator development and on the immature predator's mortality. Factors of least importance were the variances of the predator's and prey's oviposition curves, the abiotic mortality of the adult predator, the abiotic mortality of the pre-adult and adult prey, the functional response of the nymphal and adult male predators, and the effect of prey consumption on adult predator mortality. The sex ratios had little effect, except when the proportion of female predators was very low. The initial predator-prey ratio and time of predator introduction had significant impacts on system behavior, though the patterns of impact were different.     

Vacation farms and ecotourism in Saskatchewan, Canada

Vacation farms represent an increasingly significant rural diversification option for chronically unstable agriculture-based economies such as Saskatchewan. Concurrently, ecotourism is a rapidly expanding form of tourism which could serve to enhance the recreation product of such rural enterprises. Accordingly, a self-administered questionnaire was sent to all listed vacation farm operators in the province to obtain information on the provision of ecotourism opportunities. Just over one-half (n = 40) of all operations returned a completed questionnaire. Of 23 listed recreation options, wildlife viewing was cited as the activity most frequently undertaken by vacation farm visitors, followed by hunting, casual photography and touring. Wildlife viewing occurred most commonly during the spring and summer, with access to the resource occurring mainly on foot, and less so by horse and vehicle. Birds were the most important category of wildlife viewed, followed by mammals and plants; reptiles/amphibians, insects and fish were of only minor significance. It was evident that the sampled vacation farm operators possessed very little training in the area of ecotourism; few barriers or opportunities related to the latter were indicated. Appropriate recommendations include the provision of ecotourism training opportunities, stronger linkages between vacation farms and public spaces, and further investigation into the relationship between wildlife viewing and hunting activities.     

The Evolution of Organizations: Suggestions from Complexity Theory About the Interplay Between Natural Selection and Adaptation

There has been much debate in the managementliterature between neo-Darwinists (who believe in thenatural selection of populations of organizations) andadaptationists (who contend that changes in organization structure and behavior occur in response to theenvironment). The general thesis of neo-Darwinism isthat species are blindly selected for survival by theenvironment. The latest empirical support for the dominant neo-Darwinism perspective adopted bymost biologists is based primarily on the experimentsconducted by Salvador Luria who claims to haveconclusively demonstrated that genes mutate randomly.Recently, however, biologists have re-examined Luria sresearch methods and, after replications of hisexperiments, now question some aspects of the validityof his results. Moreover, there is now new researchwhich provides support for the earlier adaptationistposition, namely, the existence of evolutionary driversand directors existing within self-organizing systems.Of particular importance to the present study is the experimental indication thatself-organizing systems play a conscious role in theirown evolution. We propose that similar mechanisms orprocesses operate in organizational adaptation, thuspointing toward a theoretical modification ofneo-Darwinism that embraces both adaptation and naturalselection in a general, unified theory.     

Changes in Income Concentration: Taxes or Macroeconomic Conditions?

We examine the relative importance of tax rates and macroeconomic fluctuations in explaining the share of national adjusted gross income (AGI) reported by the top 0.5% of all taxpayers. Results indicate that cutting the top income or capital gains tax rate would increase the top AGI share but not by enough to increase revenues. The preponderance of evidence suggests that the top AGI share is affected more by the capital gains tax rate than by the income tax rate but that real gross domestic product fluctuations have even larger effects.