摘要:

The importance of disease markers in understanding the progression of acquired immune deficiency syndrome (AIDS) and devising treatment strategies is well recognized. This issue is usually addressed using cross-sectional data analysis, which tends to ignore the longitudinal data collected on the individuals. Available longitudinal data for nontransfusion-related AIDS raise some technical challenges to standard longitudinal analyses due to left and right censoring as well as left truncation. We describe a likelihood method to model the disease markers as a function of time by modeling the joint distribution of the markers, the time of infection, and the time to AIDS. We address the problems of censoring and truncation using standard survival analysis techniques. We also consider the prediction of time to AIDS given a series of disease marker measurements. An illustrative example, using data from the Toronto AIDS cohort study, is given. In particular, the analysis shows that the slope of the decline in T4 cell count measurements or T4/T8 ratio is associated with the time to AIDS. We compare the prediction of the time to AIDS for an individual with or without a series of T4/T8 measurements and with a known or unknown infection time.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476332

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The relationship between the utilization of nursing home care and its price is a subject of considerable policy interest. We assess price sensitivity by developing and applying “overlap polynomials” as a method to exploit the temporal price variation implicit in Medicare payment rules for nursing home care. Standard methods for measuring price responsiveness are inappropriate for measuring the effects of temporal price variation, and unmeasured quality variation often confounds cross-sectional price variation. Our empirical analysis assesses the magnitude of shifts in nursing home discharge rates attributable to the price changes that occur when Medicare coverage diminishes or ends. Our findings provide strong evidence that the duration of nursing home stays is sensitive to price in the population examined here.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476333

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Between 1973 and 1978, 12 states with collectively over one-third of the total U.S. population enacted laws that decriminalized the possession of marijuana. This article uses standard metropolitan statistical area (SMSA) level data on hospital emergency room drug episodes collected by the Drug Abuse Warning Network to measure the effect of changes in drug penalties on substance abuse crises. The regression models demonstrate that marijuana decriminalization was accompanied by a significant reduction in episodes involving drugs other than marijuana and an increase in marijuana episodes. Although possible biases in the data preclude firm conclusions, the results suggest that some substitution occurs towards the less severely penalized drug when punishments are differentiated.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476334

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This article explores quantity discounts and quality (purity) premia in the prices of illicit drugs. It examines several models of how drug prices might depend on transaction size. A simple relation implied by a tree model of the domestic distribution network fits data provided by the Western States Information Network for 1984–1991 quite well for various illicit drugs. Quality premia are less well explained. It is observed that price is not a function of pure quantity alone; customers pay more for 2 grams at a given purity than they do for 1 gram at double that purity. Nevertheless, some purity premia are observed for white heroin, brown heroin, and powder cocaine, although not for methamphetamines, crack, or heroin tar. The estimated coefficients reflect known phenomena such as the collapses in the prices of cocaine and black tar heroin; intuitively reasonable but undocumented phenomena, such as discounts for brown heroin near the Mexican border; and some unexpected results, such as an apparent difference between the distribution of sinsemilla and that of other cannabis products.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476335

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Current-status data are often collected for use in survival analyses, because this type of data generally is considered to be more reliable than retrospective reports of when an event occurred. Although techniques for calculating mean survival time from current-status data are well known, their use in multiple regression models is somewhat troublesome. Using data on current breast-feeding behavior, this article considers a number of techniques that have been suggested in the literature, including parametric, nonparametric, and semiparametric models as well as the application of standard schedules. Models are tested in both proportional-odds and proportional-hazards frameworks. Although the choice of models does not strongly affect the conclusions that would be drawn, I recommend that a logistic regression in which the baseline log-odds of breast-feeding by child's age are represented by a natural cubic spline should be the preferred methodology. This methodology offers a reasonable compromise between the parsimony of parametric models and the flexibility and good fit of nonparametric models. The same methodology may be well suited to other applications in which there are no theoretical reasons to use a particular parametric form.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476336

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Major league baseball in the United States is divided into two leagues and four divisions. Each team plays 162 games against teams in the same league. The winner in each division is the team winning the most games of the teams in that division. We wish to predict the division winners based on games played up to any specified time. We use a generalized choice model for the probability of a team winning a particular game that allows for different strengths for each team, different home advantages, and strengths varying randomly with time. Future strengths and the outcomes of future games are simulated using Markov chain sampling. The probability of a particular team winning the division is then estimated by counting the proportion of simulated seasons in which it wins the most games. The method is applied to the 1991 National League season.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476337

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Skip sequencing in surveys reduces costs but also acts as a mechanism of contagion in transmitting error from one survey item to subsequent items. The error process is modeled as a contagious, stochastic one in which both the initiating and induced errors follow the Poisson distribution. The resulting compound distribution, first used by Thomas in 1949, is then used as the basis of a discrete contagious regression model in which characteristics of respondents, subject individuals, and interviewers are allowed to affect the intensity of both initiating and induced errors. The model is applied to data from the 1984 Survey of Income and Program Participation (SIPP) Reinterview Program. The results suggest that induced-sequencing errors are at least as important a source of losses in reliability as are initiating-response or spontaneous-procedural errors. The relative importance of induced-sequencing errors is directly proportional to the sequence length. Because the relationships between individual characteristics and the various types of error differ significantly, conclusions based on narrow definitions of response errors do not necessarily generalize when sequencing errors are included. The regression estimates suggest that older and less educated respondents provide less reliable data. Older female interviewers, however, are found to obtain more reliable data.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476338

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

One approach to identifying outliers is to assume that the outliers have a different distribution from the remaining observations. In this article we define outliers in terms of their position relative to the model for the good observations. The outlier identification problem is then the problem of identifying those observations that lie in a so-called outlier region. Methods based on robust statistics and outward testing are shown to have the highest possible breakdown points in a sense derived from Donoho and Huber. But a more detailed analysis shows that methods based on robust statistics perform better with respect to worst-case behavior. A concrete outlier identifier based on a suggestion of Hampel is given.

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476339

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476340

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0162-1459    

DOI:10.1080/01621459.1993.10476341

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor