共查询到20条相似文献,搜索用时 15 毫秒
1.
《随机性模型》2013,29(4):491-512
In this paper we examine the spread of HIV when this disease is transmitted through the random sharing of contaminated drug injection equipment. We first model the spread of disease using a standard set of behavioral assumptions discussed by Kaplan [1]. We demonstrate that deterministic and stochastic models based on these assumptions behave very similarly and use a branching process approximation to show that if the basic reproductive number, R 0, is less than or equal to unity then the disease will always become extinct. If R 0>1 then, although the disease might take off, it is still possible for it to die out, and we calculate the probability of extinction. This is not of the simple form R 0 ?a , where a is the initial number of infectious addicts, which might have been expected from Whittle's stochastic threshold theorem [2]. We next discuss an extended model that incorporates a three-stage AIDS incubation period and again examine a branching process approximation. We finally explore the extent to which control strategies such as needle exchange and improved needle cleaning can reduce the risk of a HIV epidemic before concluding with a brief discussion. 相似文献
2.
《Econometric Reviews》2013,32(3):309-336
ABSTRACT We examine empirical relevance of three alternative asymptotic approximations to the distribution of instrumental variables estimators by Monte Carlo experiments. We find that conventional asymptotics provides a reasonable approximation to the actual distribution of instrumental variables estimators when the sample size is reasonably large. For most sample sizes, we find Bekker[11] asymptotics provides reasonably good approximation even when the first stage R 2 is very small. We conclude that reporting Bekker[11] confidence interval would suffice for most microeconometric (cross-sectional) applications, and the comparative advantage of Staiger and Stock[5] asymptotic approximation is in applications with sample sizes typical in macroeconometric (time series) applications. 相似文献
3.
《统计学通讯:模拟与计算》2013,42(3):489-511
We consider the semiparametric regression model introduced by [1]. The dependent variable y is linked to the index x′ β through an unknown link function. [1] and [2] present Slicing methods (the Sliced Inverse Regression methods SIR-I, SIR-II and SIRα) in order to estimate the direction of the unknown slope parameter β. These methods are computationally simple and fast but depend on the choice of an arbitrary slicing fixed by the user. When the sample size is small, the number and the position of slices have an influence on the estimated direction. In this paper, we suggest to use the corresponding Pooled Slicing methods: PSIR-I (proposed by [3]), PSIR-II and PSIRα. These methods combine the results from a number of slicings. We compare the sample behaviour of Slicing and Pooled Slicing methods on simulations. We also propose a practical choice of α in SIRα and PSIRα methods. 相似文献
4.
《统计学通讯:理论与方法》2013,42(10):2005-2021
In many experiments where pre-treatment and post-treatment measurements are taken, investigators wish to determine if there is a difference between two treatment groups. For this type of data, the post-treatment variable is used as the primary comparison variable and the pre-treatment variable is used as a covariate. Although most of the discussion in this paper is written with the pre-treatment variable as the covariate the results are applicable to other choices of a covariate. Tests based on residuals have been proposed as alternatives to the usual covariance methods. Our objective is to investigate how the powers of these tests are affected when the conditional variance of the post-treatment variable depends on the magnitude of the pre-treatment variable. In particular, we investigate two cases. [1] The conditional variance of the post-treatment variable gradually increases as the magnitude of the pre-treatment variable increases. (In many biological models this is the case.) [2] The conditional variance of the post-treatment variable is dependent upon natural or imposed subgroups contained within the pre-treatment variable. Power comparisons are made using Monte Carlo techniques. 相似文献
5.
《统计学通讯:模拟与计算》2013,42(4):787-803
It is known that, in the presence of short memory components, the estimation of the fractional parameter d in an Autoregressive Fractionally Integrated Moving Average, ARFIMA(p, d, q), process has some difficulties (see [1]). In this paper, we continue the efforts made by Smith et al. [1] and Beveridge and Oickle [2] by conducting a simulation study to evaluate the convergence properties of the iterative estimation procedure suggested by Hosking [3]. In this context we consider some semiparametric approaches and a parametric method proposed by Fox-Taqqu[4]. We also investigate the method proposed by Robinson [5] and a modification using the smoothed periodogram function. 相似文献
6.
Marcelo de Paula 《统计学通讯:理论与方法》2013,42(19):5762-5786
ABSTRACTIn this article, we propose an approach for incorporating continuous and discrete original outcome distributions into the usual exponential family regression models. The new approach is an extension of the works of Suissa (1991) and Suissa and Blais (1995), which present methods to estimate the risk of an event defined in a sample subspace of an original continuous outcome variable. Simulation studies are presented in order to illustrate the performance of the developed methodology. Real data sets are analyzed by using the proposed models. 相似文献
7.
《Econometric Reviews》2013,32(3):383-393
ABSTRACT This paper considers computation of fitted values and marginal effects in the Box–Cox regression model. Two methods, 1 the “smearing” technique suggested by Duan (see Ref. [10]) and 2 direct numerical integration, are examined and compared with the “naive” method often used in econometrics. 相似文献
8.
《统计学通讯:理论与方法》2013,42(9):1789-1799
Abstract In a recent article Hsueh et al. (Hsueh, H.-M., Liu, J.-P., Chen, J. J. (2001). Unconditional exact tests for equivalence or noninferiority for paired binary endpoints. Biometrics 57:478–483.) considered unconditional exact tests for paired binary endpoints. They suggested two statistics one of which is based on the restricted maximum-likelihood estimator. Properties of these statistics and the related tests are treated in this article. 相似文献
9.
Baker (2008) introduced a new class of bivariate distributions based on distributions of order statistics from two independent samples of size n. Lin and Huang (2010) discovered an important property of Baker’s distribution and showed that the Pearson’s correlation coefficient for this distribution converges to maximum attainable value, i.e., the correlation coefficient of the Fréchet upper bound, as n increases to infinity. Bairamov and Bayramoglu (2013) investigated a new class of bivariate distributions constructed by using Baker’s model and distributions of order statistics from dependent random variables, allowing higher correlation than that of Baker’s distribution. In this article, a new class of Baker’s type bivariate distributions with high correlation are constructed based on distributions of order statistics by using an arbitrary continuous copula instead of the product copula. 相似文献
10.
Prabhanjan N. Tattar 《统计学通讯:理论与方法》2013,42(5):1270-1277
AbstractIn the present paper we develop bootstrap tests of hypothesis, based on simulation, for the transition probability matrix arising in the context of a multi-state model. The bootstrap test statistic is based on the paper of Tattar and Vaman (2008), which develops a statistic for the testing problems concerning the transition probability matrix of the non homogeneous Markov process. 相似文献
11.
ABSTRACTRandom vectors with positive components are common in many applied fields, for example, in meteorology, when daily precipitation is measured through a region Marchenko and Genton (2010). Frequently, the log-normal multivariate distribution is used for modeling this type of data. This modeling approach is not appropriate for data with high asymmetry or kurtosis. Consequently, more flexible multivariate distributions than the log-normal multivariate are required. As an alternative to this distribution, we propose the log-alpha-power multivariate and log-skew-normal multivariate models. The first model is an extension for positive data of the fractional order statistics model Durrans (1992). The second one is an extension of the log-skew-normal model studied by Mateu-Figueras and Pawlowsky-Glahn (2007). We study parameter estimation for these models by means of pseudo-likelihood and maximum likelihood methods. We illustrate the proposal analyzing a real dataset. 相似文献
12.
《统计学通讯:理论与方法》2013,42(5):799-813
The local influence approach of Cook [1]to regression diagnostic is developed and discussed, and compared with Cook's [2]deletion approach. The ability of the local influence approach to handle cases simultaneously, as well as some of its theoretical and practical difficulties, are reviewed. The perturbation ideas of the approach are applied to the linear model making distinction between the local perturbations on the assumptions of the model and the data. 相似文献
13.
Pao-Sheng Shen 《统计学通讯:理论与方法》2013,42(16):4812-4823
ABSTRACTGandy and Jensen (2005) proposed goodness-of-fit tests for Aalen's additive risk model. In this article, we demonstrate that the approach of Gandy and Jensen (2005) can be applied to left-truncated right-censored (LTRC) data and doubly censored data. A simulation study is conducted to investigate the performance of the proposed tests. The proposed tests are illustrated using heart transplant data. 相似文献
14.
AbstractWe suggest shrinkage based technique for estimating covariance matrix in the high-dimensional normal model with missing data. Our approach is based on the monotone missing scheme assumption, meaning that missing values patterns occur completely at random. Our asymptotic framework allows the dimensionality p grow to infinity together with the sample size, N, and extends the methodology of Ledoit and Wolf (2004) to the case of two-step monotone missing data. Two new shrinkage-type estimators are derived and their dominance properties over the Ledoit and Wolf (2004) estimator are shown under the expected quadratic loss. We perform a simulation study and conclude that the proposed estimators are successful for a range of missing data scenarios. 相似文献
15.
S. Zinodiny 《统计学通讯:理论与方法》2018,47(22):5519-5533
The problem of estimating of the vector β of the linear regression model y = Aβ + ? with ? ~ Np(0, σ2Ip) under quadratic loss function is considered when common variance σ2 is unknown. We first find a class of minimax estimators for this problem which extends a class given by Maruyama and Strawderman (2005) and using these estimators, we obtain a large class of (proper and generalized) Bayes minimax estimators and show that the result of Maruyama and Strawderman (2005) is a special case of our result. We also show that under certain conditions, these generalized Bayes minimax estimators have greater numerical stability (i.e., smaller condition number) than the least-squares estimator. 相似文献
16.
17.
This paper is the generalization of weight-fused elastic net (Fu and Xu, 2012), which performs group variable selection by combining weight-fused LASSO(wfLasso) and elastic net (Zou and Hastie, 2005) penalties. In this study, the elastic net penalty is replaced by adaptive elastic net penalty (AdaEnet) (Zou and Zhang, 2009), and a new group variable selection algorithm with oracle property (Fan and Li, 2001; Zou, 2006) is obtained. 相似文献
18.
《统计学通讯:理论与方法》2013,42(8-9):1695-1714
A numerical specification of ‘size’ and ‘shape’ is of interest for making interpretations in morphometrics. Starting from a, possibly large, set m 1,…, mr of size measurements, e.g. m 1= height, m 2= sitting height, etc., a preliminary analysis provides the set x 1,…,xp of size measurements to be used, e.g. x 1= m 1? m 2= subischial leg length, x 2= m 2= sitting height, and x 3= head circumference. In general these xj are constructed as appropriately scaled linear combinations of the original measurements. A constant term should not be included because size measurements have to be 0 if all xj are 0. Our theory requires a (compromise) vector μof means and a matrix Σof (co)variances. Size being specified as an optimalsize characteristic of the form c ′ x , the remaining morphological information is expressed by, at most, p? 1 components of shapeof the form d ′ x. Relations with Darroch-Mosimann [9]are indicated. An application to human growth is made and other applications are suggested. Don't read my book, think for yourself. C. R. Rao, personal communications, 1981 相似文献
19.
A NOTE ON ESTIMATING THE NUMBER OF SUPERIMPOSED EXPONENTIAL SIGNALS BY THE CROSS-VALIDATION APPROACH
《统计学通讯:理论与方法》2013,42(8-9):1579-1589
In this paper, a procedure based on the delete-1 cross-validation is given for estimating the number of superimposed exponential signals, its limiting behavior is explored and it is shown that the probability of overestimating the true number of signals is greater than a positive constant for sufficiently large samples. Also a general procedure based on the cross-validation is presented when the deletion proceeds according to a collection of subsets of indices. The result is similar to the delete-1 cross-validation if the number of deletions is fixed. The simulation results are provided for the performance of the procedure when the collections of subsets of indices are chosen as those suggested by Shao [1]in a linear model selection problem. 相似文献
20.
ABSTRACTIn this article, the linear models with measurement error both in the response and in the covariates are considered. Following Shalabh et al. (2007, 2009), we propose several restricted estimators for the regression coefficients. The consistency and asymptotic normality of the restricted estimators are established. Furthermore, we also discuss the superiority of the restricted estimators to unrestricted estimators under Pitman closeness criterion. We also develop several variance estimators and establish their asymptotic distributions. Wald-type statistics are constructed for testing the linear restrictions. Finally, Monte Carlo simulations are conducted to illustrate the finite-sample properties of the proposed estimators. 相似文献