Bayesian prediction of waiting times in stochastic models

The authors show how saddlepoint techniques lead to highly accurate approximations for Bayesian predictive densities and cumulative distribution functions in stochastic model settings where the prior is tractable, but not necessarily the likelihood or the predictand distribution. They consider more specifically models involving predictions associated with waiting times for semi‐Markov processes whose distributions are indexed by an unknown parameter θ. Bayesian prediction for such processes when they are not stationary is also addressed and the inverse‐Gaussian based saddlepoint approximation of Wood, Booth & Butler (1993) is shown to accurately deal with the nonstationarity whereas the normal‐based Lugannani & Rice (1980) approximation cannot, Their methods are illustrated by predicting various waiting times associated with M/M/q and M/G/1 queues. They also discuss modifications to the matrix renewal theory needed for computing the moment generating functions that are used in the saddlepoint methods.     

Sex similarities in occupational status attainment: Are the results due to the restriction of the sample to employed women?

Research on sex differences in occupational attainment suggests that working men and working women attain essentially the same mean level of occupational attainment and do so through quite similar processes. A possible explanation for these similarities is that the sample of working women contains an overrepresentation of successful women, since women who can afford not to work will stay out of the labor force unless they find a job commensurate with their education. This we define as a censoring problem. By extending a technique developed by Heckman, we can estimate the structural parameters for all women, regardless of current employment status. This procedure allows us to assess the impact of the censoring problem on women's occupational attainment equations.     

Residential preferences and population distribution

Public opinion research has revealed decided preferences for living in rural areas and small towns, and proponents of population deconcentration have interpreted this as support for their policies. This study, based on a national sample, yielded similar results, but when we introduced the additional possibility of a preference for proximity to a larger city, then the rural areas preferred were found, for most respondents, to be those within the commuting range of a metropolitan central city. Although persons wishing to live near large cities were found to be looking for the same qualities of living sought by those who prefer a more remote location, these findings are not, in general, consistent with the argument that public preferences support strategies of population dispersal into nonmetropolitan areas. Instead they indicate that most of those who wish to live in a different location favor the peripheral metropolitan ring areas that have, in fact, been growing rapidly by in-migration.     

Congestion,quality deterioration,and optimal use: Wilderness recreation in the Spanish peaks primitive area

With increasing demand for low-density recreational services and limited supply of facilities to provide them, congestion is becoming an important management problem. The purpose of this paper is to outline a model of congestion, estimate the effect of it upon individual willingness to pay for wilderness experiences, and illustrate how these results might be used for efficient management. A survey of users of the Spanish Peaks Primitive Area indicates that their revealed willingness to pay is significantly affected by encroachments upon the solitude they experience during their trip. Consequently, congestion effects for such services can be measured and used in the formation of administrative policy.     

Effects of Group Practice of the Transcendental Meditation Program on Preventing Violent Crime in Washington,D.C.: Results of the National Demonstration Project,June--July 1993

This paper reports the results of a prospective experiment in which a group of approximately 4,000 participants in the Transcendental Meditation and TM-Sidhi programs of Maharishi Mahesh Yogi assembled in Washington, D.C., from June 7 to July 30, 1993. It was hypothesized that levels of violent crime in the District of Columbia would fall substantially during the Demonstration Project, as a result of the group's effect of increasing coherence and reducing stress in the collective consciousness of the District. A 27-member Project Review Board comprising independent scientists and leading citizens approved the research protocol and monitored the research process. Weekly crime data was derived from database records provided by the District of Columbia Metropolitan Police Department (DCMPD), which are used in the FBI Uniform Crime Reports. Statistical analysis considered the effect of weather variables, daylight, historical crime trends and annual patterns in the District of Columbia, as well as trends in neighboring cities. Consistent with previous research, levels of homicides, rapes and assaults (HRA crimes) correlated with average weekly temperature. Robberies approximately followed an annually recurring cycle. Time series analysis of 1993 data, controlling for temperature, showed that HRA crimes dropped significantly during the Demonstration Project, corresponding with increases in the size of the group; the maximum decrease was 23.3% (p < 2 × 10–9) [24.6% using a longer baseline, with 1988--1993 data (p < 3 × 10–5)], coincident with the peak number of participants in the group during the final week of the assembly. When the same period in each of the five previous years was examined, no significant decreases in HRA crimes were found. Robberies did not decrease significantly. However, a model that jointly estimated the effect of the Demonstration Project on both HRA crimes and robberies showed a significant reduction in violent crimes overall of 15.6% (p = 0.0008). Further analysis showed that the effect of the coherence-creating group on reducing HRA crimes could not be accounted for by additional police staffing. The time series analysis for HRA crimes gave results that are highly robust to alternative model specifications, and showed that the effect of the group size was cumulative and persisted after the Demonstration Project ended. Also, calculation of the steady state gain based on the time series model predicted that a permanent group of 4,000 coherence-creating experts in the District would have a long-term effect of reducing HRA crimes by 48%.     

Reexamining the moving to opportunity study and its contribution to changing the distribution of poverty and ethnic concentration

For the past decade and a half a concerted effort has been undertaken to determine whether policy interventions in residential location can solve the problems of inner-city poverty and racial concentration. Studies based on data from the Gautreaux litigation and the U.S. Department of Housing and Urban Development (HUD)-sponsored Moving to Opportunity (MTO) program have provided an overall optimistic interpretation of the possibilities of improving inner-city lives via mobility vouchers and counseling. A reanalysis of the data from the MTO program, focusing specifically on African American households, suggests greater caution in the interpretation of the findings from either Gautreaux or the MTO program. No statistically significant difference exists between the percentage of poor or the percentage of African Americans in the current neighborhoods between MTO and Section 8 experimental groups. In some cases, there is no statistically significant difference between those who move with a voucher and those who move without any assistance at all. Although there is some evidence that MTO programs have brought specific gains for individual families, claims for the MTO program as a whole need to be treated with a great deal more caution than they have been to date.     

Health care issues among lesbian, gay, bisexual, transgender and intersex (LGBTI) populations in the United States: Introduction

This supplemental issue of the Journal of Homosexuality presents research that explores a variety of health care issues encountered by lesbian, gay, bisexual, transgender and intersex (LGBTI) population groups in the United States over the 10-year period from 1993 to 2002. Topics include access to health care, utilization of care, training of medical and mental health providers, and the appropriate preparation of clinical offices and waiting areas. Authors used a variety of community-based public health research methods, including participant and provider surveys and retrospective chart reviews of patients, to develop this body of research, providing a recent-historical perspective on the complex health care and health-related needs of sexual and gender minorities. Particularly for transgender and intersex populations, the state of research describing their health care needs is in its infancy, and much remains to be done to design effective medical and mental health programs and interventions.     

The exponential distribution analog of the Grubbs–Weaver method

Abstract

Grubbs and Weaver (1947 Grubbs, F. E., and C. L. Weaver. 1947. The best unbiased estimate of population standard deviation based on group ranges. Journal of the American Statistical Association 42 (238):224–41. doi: 10.2307/2280652.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) suggest a minimum-variance unbiased estimator for the population standard deviation of a normal random variable, where a random sample is drawn and a weighted sum of the ranges of subsamples is calculated. The optimal choice involves using as many subsamples of size eight as possible. They verified their results numerically for samples of size up to 100, and conjectured that their “rule of eights” is valid for all sample sizes. Here we examine the analogous problem where the underlying distribution is exponential and find that a “rule of fours” yields optimality and prove the result rigorously.