ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478778

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A non-Gaussian autoregressive-like model is presented for time series that exhibit occasional large increases in value, termedpulses, and exponential decay between pulses. The model differs from a first-order autoregressive process in its incorporation of feedback between the distribution of the current innovation and the history of the process. Likelihood-based methods of inference for the model are developed, and an application to endocrinological data is given.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478779

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In some epidemiologic studies, identification of individuals for study is dependent on the occurrence of some event. Once an individual is identified, the time of a previous event, termed aninitiating event, is determined retrospectively. This article considers problems of estimation when initiating events occur as a nonhomogeneous Poisson process, and the timesfrom the initiating event to the final event has pdff(s) independent of the time of the initiating event. A simple form for the likelihood function is obtained and methods of parametric and nonparametric estimation are developed and considered. In particular, the model is related to a Poisson process in the plane, and for the parametric case simple algorithms are developed for parameter estimation. Regression models are also considered as well as various generalizations of the basic problem. Parallel to the theoretical development, data on patients diagnosed with acquired immune deficiency syndrome (AIDS) are considered and a detailed analysis is given. The data report the dates of diagnosis with AIDS and infection with human immunodeficiency virus, for patients reported to the Centers of Disease Control in Atlanta, Georgia, and thought to be infected by blood or blood-product transfusion. The analysis of these data was considered by Medley, Anderson, Cox, and Billard (1987), Lui et al. (1986), and others. It is shown that nonparametric analysis leads to simple estimates of certain parameters and indicates clearly the nature of an identifiability problem that arises with data of this kind. Problems arise in the estimation of the total number of infectives or percentiles of the distribution of the induction period,s.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478780

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Clustered data occur frequently in statistical practice. In some areas of application, such as ophthalmology, clustered data are the rule rather than the exception. In this setting, standard multivariate methods such as logistic regression are invalid, because of the lack of independence among outcomes for individual sample points within a cluster. In Rosner (1984), a polychotomous logistic regression model was presented to control for the effect of both cluster and individual-specific covariates while accounting for the correlation among units within a cluster. This model reduces to a beta-binomial model in the absence of covariates, and to an ordinary logistic model for clusters of size 1 and for larger clusters when no correlation is present. A 1 level of nesting correlation structure is assumed, as is typically found in ophthalmology, where the person is the cluster and the individual eyes are the units within a cluster. In this article, this model is generalized to a 2 level of nesting structure. This model is motivated by an ophthalmologic application, where data are collected in family units and one wishes to model simultaneously the correlation at the first level of nesting among persons within a family, and at the second level of nesting between eyes within a person. In the absence of covariates, the model is characterized by a compound beta-binomial distribution that generalizes the beta-binomial distribution to more than one level of nesting. The compound beta-binomial distribution is then augmented in a regression setting, to allow for the presence of family-, person-, and eye-specific covariates while controlling for correlation at each level of nesting. Extensions to more than two levels of nesting are also considered.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478781

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The potential magnitude of publication bias has been examined with a consecutive sample of published cancer clinical trials. The analysis is based on the premise that the magnitude of the true treatment effect is unrelated to design features of the study, in particular sample size. This assumption permits an analysis based only on published studies. Three primary endpoints are examined: overall patient survival, disease-free survival, and tumor response rate. There are striking trends for each endpoint, with small studies appearing to possess large treatment effects and large studies possessing relatively small effects. It is believed that these differences are primarily due to publication bias. The bias is very large: Absolute differences observed were 41% for overall survival, 79% for disease-free survival, and 17% for response rates. Other study features have been examined that might be associated with bias, or that might be responsible for the striking trends regarding sample size. The results indicate that absence of randomization leads to significant bias, and studies conducted in a single institution are somewhat more prone to bias than multiinstitutional studies, though the trends are less consistent in the latter case. No strong trend was observed for journal type. Nevertheless, none of these variables could account for the strong effect of sample size. Sensitivity analyses of the results were conducted and alternative models were considered. These analyses generally support the contention that the magnitude of the bias due to sample size cannot be explained by alternative factors. An implication of this study is that the results of small published studies are typically unreliable, even taking into account the fact that such trials are imprecise due to sampling variation.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478782

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In this article, accumulated sudden infant death syndrome (SIDS) data, from 1974–1978 and 1979–1984 for the counties of North Carolina, are analyzed. After a spatial exploratory data analysis, Markov random-field models are fit to the data. The (spatial) trend is meant to capture the large-scale variation in the data, and the variance and spatial dependence are meant to capture the small-scale variation. The trend could be a function of other explanatory variables or could simply be modeled as a function of spatial location. Both models are fit and compared. The results give an excellent illustration of a phenomenon already well-known in time series, that autocorrelation in data can be due to an undiscovered explanatory variable. Indeed, for 1974–1978 we confirm a dependence of SIDS rate on proportion of nonwhite babies born, along with insignificant spatial correlation. Without this regressor variable, however, the spatial correlation is significant. In 1979–1984, perhaps due to reporting bias or the effect of public-education programs in infant health, the proportion of nonwhite babies born is no longer an important explanatory variable. SIDS is currently a leading category of postneonatal death, yet its cause is still a mystery. It accounts for about 7,000 deaths a year in the United States, taking the lives of about two infants per 1,000 live births. In contrast to the usual pathologic and physiologic studies of SIDS, this article takes an epidemiologic approach, using data available at the county level. The SIDS data analyzed are in a form that is representative of many problems encountered in the health and social sciences. Counts of individuals from a known or estimated base occur in epidemiologic studies (e.g., consider cancer incidence in a particular year, from the base of population years at risk, for U.S. counties), census surveys (e.g., for assessing undercount consider the dual-system estimate of uncounted people in a decennial census, from the base of total number of people, for U.S. states), and so forth. It is hoped that the spatial methods presented will prove useful in a variety of such problems.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478783

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Some researchers argue that data obtained using magnitude estimation have metric properties superior to those of data obtained using traditional survey items. The analysis in this article examines evidence relevant to the assumptions that respondents can express ratios using numbers, can locate an internal continuum, and can use the standard stimulus effectively. The data are answers to 5 practice items designed to teach magnitude estimation using line lengths and up to 18 items about stress experienced in caring for a sick person. The five practice items provide evidence of respondents' ability to give numeric estimates: 28% gave at least one answer that falls outside fairly tolerant boundaries that define a reasonable answer. Other results indicate that respondents do not improve with practice, that accuracy on the practice items does not predict good performance on magnitude estimates of a subjective property, and that respondents for whom the standard stress stimulus was hypothetical were more likely than others to answer inappropriately. Scale values calculated as medians or geometric means are accurate for the practice items and at least sensible for the care-giving items. Evaluating individual-level scores is more difficult. On the one hand, using a single point estimate entails considerable error, and unscalable answers may have disproportionate effects on individual level statistics. Furthermore, older, less educated, and male respondents find providing magnitude estimates difficult, possibly biasing analysis of individual scores. On the other hand, magnitude estimates may preserve important distinctions among individuals and may be less susceptible to bias arising from group differences in the use of the phrases attached to category ratings.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478784

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A test census of Tampa, Florida and an independent postenumeration survey (PES) were conducted by the U.S. Census Bureau in 1985. The PES was a stratified block sample with heavy emphasis placed on hard-to-count population groups. Matching the individuals in the census to the individuals in the PES is an important aspect of census coverage evaluation and consequently a very important process for any census adjustment operations that might be planned. For such an adjustment to be feasible, record-linkage software had to be developed that could perform matches with a high degree of accuracy and that was based on an underlying mathematical theory. A principal purpose of the PES was to provide an opportunity to evaluate the newly implemented record-linkage system and associated methodology. This article discusses the theoretical and practical issues encountered in conducting the matching operation and presents the results of that operation. A review of the theoretical background of the record-linkage problem provides a framework for discussions of the decision procedure, file blocking, and the independence assumption. The estimation of the parameters required by the decision procedure is an important aspect of the methodology, and the techniques presented provide a practical system that is easily implemented. The matching algorithm (discussed in detail) uses the linear sum assignment model to “pair” the records. The Tampa, Florida, matching methodology is described in the final sections of the article. Included in the discussion are the results of the matching itself, an independent clerical review of the matches and nonmatches, conclusions, problem areas, and future work required.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478785

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Four different preliminary estimators are employed by the National Agricultural Statistics Service of the U.S. Department of Agriculture to obtain the final estimate of livestock inventories of major states. To combine these four estimators a composite estimator (which is a weighted average) is proposed. Two types of composite estimators—one with fixed weights, the other with adaptive weights—are investigated. The composite estimator with adaptive weights is derived by minimizing a quadratic function subject to linear constraints. The variance and mean squared error of the composite estimator with adaptive weights are evaluated by the jackknife method. Numerical results based on the data from the 1984 June Enumerative Survey conducted by the Department of Agriculture support the use of composite estimation.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478786

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Most population statistics for states, counties, and cities refer to permanent residents, or persons who spend most of their time in an area. At certain times, however, many states and local areas have large numbers of temporary residents who exert a significant impact on the area's economy, physical environment, and quality of life. Typically, very little is known about the number, timing, and characteristics of these residents. This study discusses the problems of defining and estimating temporary residents, focusing on the strengths and weaknesses of a number of data sources and estimation techniques. It closes with an assessment of the potential usefulness of developing methods to estimate temporary residents.

ISSN:0162-1459    

DOI:10.1080/01621459.1989.10478787

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor