摘要:

Economists and psychologists have recently been developing new theories of decision making under uncertainty that can accommodate the observed violations of standard statistical decision theoretic axioms by experimental subjects. We propose a procedure that finds a collection of decision rules that best explain the behavior of experimental subjects. The procedure is a combination of maximum likelihood estimation of the rules together with an implicit classification of subjects to the various rules and a penalty for having too many rules. We apply our procedure to data on probabilistic updating by subjects in four different universities. We get remarkably robust results showing that the most important rules used by the subjects (in order of importance) are Bayes's rule, a representativeness rule (ignoring the prior), and, to a lesser extent, conservatism (overweighting the prior).

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476620

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Hematopoiesis is the body's way of making the cellular constituents of blood. Oxygen transport, response to infections, and control of bleeding are among the functions of different mature blood cells. These specific functions are acquired as cells mature in the bone marrow. Stem cells are the “master cells” at the top of this pedigree, having within them the capacity to reconstitute the entire system. Although the latter stages of hematopoiesis are fairly well understood, the functioning of stem cells and other multipotential cells is currently a matter of intense research. This article presents a statistical analysis providing support for the clonal succession model of early hematopoiesis. J. L. Abkowitz and colleagues at the University of Washington have developed an experimental method for studying the kinetics of early hematopoiesis in a hybrid cat. The essence of the method is to analyze G6PD, an enzyme linked to the X chromosome. The G6PD type of a cell forms a binary marker that is passed down to all its descendant cells. Data record time series of proportions of one G6PD type in cells from the bone marrow, providing information about the number and lifetime of unobservable stem cells. Studies were performed after the autologous transplantation of G6PD heterozygous cats with limited numbers of hematopoietic stem cells. Preliminary analysis of the observed proportions indicates that under these circumstances, the proportion of cells with one type of G6PD is not constant over time. A simple stochastic model is used to quantify the relationship between observed proportions and unobserved stem cell populations. The model has a hidden Markov structure. We develop parameter estimates, confidence sets, and goodness-of-fit tests for this model. For our simple model, a recursive updating algorithm allows computation of the multimodal likelihood functions. A similar algorithm produces estimates of the realized Markov process. The parametric bootstrap is used to calibrate likelihood-based confidence sets and to perform simple goodness-of-fit tests. We address the question of whether stem cells have a constant proliferative potential between cats, and we discuss criticisms of the simple model.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476621

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A wealth of data concerning life's basic molecules, proteins and nucleic acids, has emerged from the biotechnology revolution. The human genome project has accelerated the growth of these data. Multiple observations of homologous protein or nucleic acid sequences from different organisms are often available. But because mutations and sequence errors misalign these data, multiple sequence alignment has become an essential and valuable tool for understanding structures and functions of these molecules. A recently developed Gibbs sampling algorithm has been applied with substantial advantage in this setting. In this article we develop a full Bayesian foundation for this algorithm and present extensions that permit relaxation of two important restrictions. We also present a rank test for the assessment of the significance of multiple sequence alignment. As an example, we study the set of dinucleotide binding proteins and predict binding segments for dozens of its members.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476622

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the biomedical products industry, measures of the quality of individual clinical specimens or manufacturing production units are often available in the form of high-dimensional data such as continuous recordings obtained from an analytical instrument. These recordings are then examined by experts in the field who extract certain features and use these to classify individuals. To formalize and quantify this procedure, an approach for extracting features from recordings based on nonparametric regression is described. These features are then used to build a classification model that incorporates the knowledge of the expert. The procedure is illustrated with the problem of grading of syringes from associated friction profile data. Features of the syringe friction profiles used in the classification are extracted via smoothing splines, and grades of the syringes are assigned by an expert tribologist. A nonlinear classification model is constructed to predict syringe grades based on the extracted features. The classification model makes it possible to grade syringes automatically without expert inspection. Using leave-one-out cross-validation, the prediction accuracy of the classification model is found to be about the same as the accuracy obtained from the expert.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476623

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The shape of a regression curve can to a large extent be characterized by the succession of structural features like extrema, inflection points, and so on. When analyzing a sample of regression curves, it is often important to know at an early stage of data analysis which structural features are occurring consistently in each curve of the sample. Such a definition is usually not easy due to substantial interindividual variation both in thexand theyaxis and due to the influence of noise. A method is proposed for identifying typical features without relying on an a priori specified functional model for the curves. The approach is based on the frequencies of occurrence of structural features, as, for example, maxima in the curve sample along thexaxis. Important tools are nonparametric regression and differentiation and kernel density estimation. Apart from a theoretical foundation, the usefulness of the method is documented by application to two interesting biomedical areas: growth and development, and neurophysiology.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476624

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A prediction method is given for a first- and second-order nonstationary spatio-temporal process. The predictor uses local data only and consists of a two-stage generalized regression estimate of the local drift at the prediction location added to a kriging prediction of the residual process at that location. This predictor is applied to observations on seasonal, rainfall-deposited sulfate over the conterminous United States between summer 1986 and summer 1992. Analyses suggest that predictions and estimated prediction standard errors have negligible to small biases, there is spatially heterogeneous temporal drift, and temporal covariance is negligible.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476625

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We attempt to recover a function of unknown smoothness from noisy sampled data. We introduce a procedure,SureShrink, that suppresses noise by thresholding the empirical wavelet coefficients. The thresholding is adaptive: A threshold level is assigned to each dyadic resolution level by the principle of minimizing the Stein unbiased estimate of risk (Sure) for threshold estimates. The computational effort of the overall procedure is orderN· log(N) as a function of the sample sizeN. SureShrinkis smoothness adaptive: If the unknown function contains jumps, then the reconstruction (essentially) does also; if the unknown function has a smooth piece, then the reconstruction is (essentially) as smooth as the mother wavelet will allow. The procedure is in a sense optimally smoothness adaptive: It is near minimax simultaneously over a whole interval of the Besov scale; the size of this interval depends on the choice of mother wavelet. We know from a previous paper by the authors that traditional smoothing methods—kernels, splines, and orthogonal series estimates—even with optimal choices of the smoothing parameter, would be unable to perform in a near-minimax way over many spaces in the Besov scale. Examples ofSureShrinkare given. The advantages of the method are particularly evident when the underlying function has jump discontinuities on a smooth background.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476626

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Generalized linear models (GLM's) are simple, convenient models for count data, but they assume that the variance is a specified function of the mean. Although overdispersed GLM's allow more flexible mean-variance relationships, they are often not as simple to interpret nor as easy to fit as standard GLM's. This article introduces a convexity plot, orCplot for short, that detects overdispersion and relative variance curves and relative variance tests that help to understand the nature of the overdispersion. Convexity plots sometimes detect overdispersion better than score tests, and relative variance curves and tests sometimes distinguish the source of the overdispersion better than score tests.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476627

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We propose two tests for testing homogeneity among clustered data adjusting for the effects of covariates. The first is a score test for a generalized linear model with random effect, in which the distribution of the response variable given the random effect is entirely defined. In contrast to the likelihood ratio test, however, the score test does not require estimation of the parameters of a mixed-effects model nor specification of the mixing distribution. The second test is proposed in the framework of the generalized estimating equation (GEE) approach. In deriving this test, we need only the specification of the marginal expectation and variance of the response variable and the fourth moment for the overdispersion term, whereas for deriving the score test for mixed effects models, the entire conditional distribution must be specified. We demonstrate that the two tests are identical when the covariance matrix assumed in the GEE approach is that of the random-effects model. In both approaches, the test statistic can be decomposed into a pairwise correlation statistic and a statistic of overdispersion. We performed a simulation study to compare the power of the score test and of the test based on their pairwise correlation statistic only, and also to compare their type I errors in cases where data present overdispersion not due to the clustering studied. On the basis of these results, we recommend using the pairwise correlation statistic, which is more robust than the complete statistic to overdispersion not due to the clustering studied.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476628

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This article provides theoretical support for our simulation-based estimation procedure, SIMEX, for measurement error models. We do so by establishing a strong relationship between SIMEX estimation and jackknife estimation. A result of our investigation is the identification of a variance estimation method for SIMEX that parallels jackknife variance estimation. Data from the Framingham Heart Study are used to illustrate the variance estimation procedure in logistic regression measurement error models.

ISSN:0162-1459    

DOI:10.1080/01621459.1995.10476629

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor