EM algorithms for beta kernel distributions

The EM algorithm is employed to compute maximum-likelihood estimates for beta kernel distributions. Estimation is considered under two censoring schemes: the progressive Type-I censoring and progressive Type-II right censoring schemes. As an application, the EM algorithm is executed to obtain maximum-likelihood estimates for the beta Weibull distribution under the two censoring schemes. A simulation study and two real data sets are used to show the efficiency of the EM algorithm.     

A comparison between the simulated annealing and the EM algorithms in normal mixture decompositions

We compare the performances of the simulated annealing and the EM algorithms in problems of decomposition of normal mixtures according to the likelihood approach. In this case the likelihood function has multiple maxima and singularities, and we consider a suitable reformulation of the problem which yields an optimization problem having a global solution and at least a smaller number of spurious maxima. The results are compared considering some distance measures between the estimated distributions and the true ones. No overwhelming superiority of either method has been demonstrated, though in one of our cases simulated annealing achieved better results.     

Constrained monotone EM algorithms for mixtures of multivariate <Emphasis Type="Italic">t</Emphasis> distributions

Mixtures of multivariate t distributions provide a robust parametric extension to the fitting of data with respect to normal mixtures. In presence of some noise component, potential outliers or data with longer-than-normal tails, one way to broaden the model can be provided by considering t distributions. In this framework, the degrees of freedom can act as a robustness parameter, tuning the heaviness of the tails, and downweighting the effect of the outliers on the parameters estimation. The aim of this paper is to extend to mixtures of multivariate elliptical distributions some theoretical results about the likelihood maximization on constrained parameter spaces. Further, a constrained monotone algorithm implementing maximum likelihood mixture decomposition of multivariate t distributions is proposed, to achieve improved convergence capabilities and robustness. Monte Carlo numerical simulations and a real data study illustrate the better performance of the algorithm, comparing it to earlier proposals.     

Standard errors for EM estimation

The EM algorithm is a popular method for computing maximum likelihood estimates. One of its drawbacks is that it does not produce standard errors as a by-product. We consider obtaining standard errors by numerical differentiation. Two approaches are considered. The first differentiates the Fisher score vector to yield the Hessian of the log-likelihood. The second differentiates the EM operator and uses an identity that relates its derivative to the Hessian of the log-likelihood. The well-known SEM algorithm uses the second approach. We consider three additional algorithms: one that uses the first approach and two that use the second. We evaluate the complexity and precision of these three and the SEM in algorithm seven examples. The first is a single-parameter example used to give insight. The others are three examples in each of two areas of EM application: Poisson mixture models and the estimation of covariance from incomplete data. The examples show that there are algorithms that are much simpler and more accurate than the SEM algorithm. Hopefully their simplicity will increase the availability of standard error estimates in EM applications. It is shown that, as previously conjectured, a symmetry diagnostic can accurately estimate errors arising from numerical differentiation. Some issues related to the speed of the EM algorithm and algorithms that differentiate the EM operator are identified.     

An EM and a Stochastic Version of the EM Algorithm for Nonparametric Hidden Semi-Markov Models

The Hidden semi-Markov models (HSMMs) were introduced to overcome the constraint of a geometric sojourn time distribution for the different hidden states in the classical hidden Markov models. Several variations of HSMMs were proposed that model the sojourn times by a parametric or a nonparametric family of distributions. In this article, we concentrate our interest on the nonparametric case where the duration distributions are attached to transitions and not to states as in most of the published papers in HSMMs. Therefore, it is worth noticing that here we treat the underlying hidden semi-Markov chain in its general probabilistic structure. In that case, Barbu and Limnios (2008 Barbu , V. , Limnios , N. ( 2008 ). Semi-Markov Chains and Hidden Semi-Markov Models Toward Applications: Their Use in Reliability and DNA Analysis . New York : Springer . [Google Scholar]) proposed an Expectation–Maximization (EM) algorithm in order to estimate the semi-Markov kernel and the emission probabilities that characterize the dynamics of the model. In this article, we consider an improved version of Barbu and Limnios' EM algorithm which is faster than the original one. Moreover, we propose a stochastic version of the EM algorithm that achieves comparable estimates with the EM algorithm in less execution time. Some numerical examples are provided which illustrate the efficient performance of the proposed algorithms.     

Quantile Regression via the EM Algorithm

The three-parameter asymmetric Laplace distribution (ALD) has received increasing attention in the field of quantile regression due to an important feature between its location and asymmetric parameters. On the basis of the representation of the ALD as a normal-variance–mean mixture with an exponential mixing distribution, this article develops EM and generalized EM algorithms, respectively, for computing regression quantiles of linear and nonlinear regression models. It is interesting to show that the proposed EM algorithm and the MM (Majorization–Minimization) algorithm for quantile regressions are really the same in terms of computation, since the updating formula of them are the same. This provides a good example that connects the EM and MM algorithms. Simulation studies show that the EM algorithm can successfully recover the true parameters in quantile regressions.     

Improving the EM algorithm for mixtures

One of the estimating equations of the Maximum Likelihood Estimation method, for finite mixtures of the one parameter exponential family, is the first moment equation. This can help considerably in reducing the labor and the cost of calculating the Maximum Likelihood estimates. In this paper it is shown that the EM algorithm can be substantially improved by using this result when applied for mixture models. A short discussion about other methods proposed for the calculation of the Maximum Likelihood estimates are also reported showing that the above findings can help in this direction too.     

Parabolic acceleration of the EM algorithm

A new acceleration scheme for optimization procedures is defined through geometric considerations and applied to the EM algorithm. In many cases it is able to circumvent the problem of stagnation. No modification of the original algorithm is required. It is simply used as a software component. Thus the new scheme can be easily implemented to accelerate a fixed point algorithm maximizing some objective function. Some practical examples and simulations are presented to show its ability to accelerate EM-type algorithms converging slowly.     

Recursive online EM estimation of mixture autoregressions

This paper develops a recursive expectation–maximization (REM) algorithm for estimating a mixture autoregression (MAR) with an independent and identically distributed regime transition process. The proposed method, which is useful for long time series as well as for data available in real time, follows a recursive predictor error-type scheme. Based on a slightly modified system to the expectation–maximization (EM) equations for an MAR model, the REM algorithm consists of two steps at each iteration: the expectation step, in which the current unobserved regime transition is estimated from new data using previous recursive estimates, and the minimization step, in which the MAR parameter estimates are recursively updated following a minimization direction. Details of implementation of the REM algorithm are given and its finite-sample performance is shown via simulation experiments. In particular, the EM and REM provide roughly similar estimates, especially for moderate and long time series.     

Structural comparative calibration using the EM algorithm

The problem of comparing the linear calibration equations of several measuring methods, each designed to measure the same characteristic on a common group of individuals, is discussed. We consider the factor analysis version of the model and propose to estimate the model parameters using the EM algorithm. The equations that define the 'M' step are simple to implement and computationally in expensive, requiring no additional maximization procedures. The derivation of the complete data log-likelihood function makes it possible to obtain the expected and observed information matrices for any number p(> 3) of instruments in closed form, upon which large sample inference on the parameters can be based. Re-analysis of two actual data sets is presented.     

Linear Quantile Regression Based on EM Algorithm

This article aims to put forward a new method to solve the linear quantile regression problems based on EM algorithm using a location-scale mixture of the asymmetric Laplace error distribution. A closed form of the estimator of the unknown parameter vector β based on EM algorithm, is obtained. In addition, some simulations are conducted to illustrate the performance of the proposed method. Simulation results demonstrate that the proposed algorithm performs well. Finally, the classical Engel data is fitted and the Bootstrap confidence intervals for estimators are provided.     

分位贸易引力模型及其EM算法分析

贸易引力模型是一种流行的具有经济理论基础的技术手段。在贸易引力模型的基础上引入分位回归的思想,构建考虑隐变量的分位贸易引力模型,采用该模型的创新之处在于:考虑基础贸易引力模型存在除距离、两国经济规模之外的隐变量,因此采用EM算法对参数进行估计。将该模型应用于2014—2018年45个样本国家的双边出口贸易额数据的分析当中,验证该模型具有稳健性,并得出以下研究结论:出口国经济规模、进口国经济规模、距离对双边出口贸易的影响符合国际贸易理论,而隐变量的系数呈现倒U型,表明除距离及两国经济规模的影响因素外存在其他影响因素,对出口贸易额存在速度先递增、后递减的作用;经过验证各系数均服从Logistc分布。     

Stochastic approximation Monte Carlo EM for change-point analysis

In the expectation–maximization (EM) algorithm for maximum likelihood estimation from incomplete data, Markov chain Monte Carlo (MCMC) methods have been used in change-point inference for a long time when the expectation step is intractable. However, the conventional MCMC algorithms tend to get trapped in local mode in simulating from the posterior distribution of change points. To overcome this problem, in this paper we propose a stochastic approximation Monte Carlo version of EM (SAMCEM), which is a combination of adaptive Markov chain Monte Carlo and EM utilizing a maximum likelihood method. SAMCEM is compared with the stochastic approximation version of EM and reversible jump Markov chain Monte Carlo version of EM on simulated and real datasets. The numerical results indicate that SAMCEM can outperform among the three methods by producing much more accurate parameter estimates and the ability to achieve change-point positions and estimates simultaneously.     

Least absolute deviations estimation via the EM algorithm

This paper derives EM and generalized EM (GEM) algorithms for calculating least absolute deviations (LAD) estimates of the parameters of linear and nonlinear regression models. It shows that Schlossmacher's iterative reweighted least squares algorithm for calculating LAD estimates (E.J. Schlossmacher, Journal of the American Statistical Association 68: 857–859, 1973) is an EM algorithm. A GEM algorithm for computing LAD estimates of the parameters of nonlinear regression models is also provided and is applied in some examples.     

A dynamic EM algorithm for estimating mixture proportions

We investigate the use of a dynamic form of the EM algorithm to estimate proportions in finite mixtures of known distributions. We prove a consistency result for this algorithm, which employs only a single EM update for each new observation. Our aim is to demonstrate that the slow convergence rate of the EM algorithm in many applications is of little practical consequence in a situation when data is frequently being updated.     

Combinatorial analysis of the adaptive last particle method

The adaptive last particle method is a simple and interesting alternative in the class of general splitting algorithms for estimating tail distributions. We consider this algorithm in the space of trajectories and for general reaction coordinates. Using a combinatorial approach in discrete state spaces, we demonstrate two new results. First, we are able to give the exact expression of the distribution of the number of iterations in an perfect version of the algorithm where trajectories are i.i.d. This result is an improvement of previous known results when the cumulative distribution function has discontinuities. Second, we show that an effective computational version of the algorithm where trajectories are no more i.i.d. follows the same statistics than the idealized version when the reaction coordinate is the committor function.     

Stochastic boosting algorithms

In this article we develop a class of stochastic boosting (SB) algorithms, which build upon the work of Holmes and Pintore (Bayesian Stat. 8, Oxford University Press, Oxford, 2007). They introduce boosting algorithms which correspond to standard boosting (e.g. Bühlmann and Hothorn, Stat. Sci. 22:477–505, 2007) except that the optimization algorithms are randomized; this idea is placed within a Bayesian framework. We show that the inferential procedure in Holmes and Pintore (Bayesian Stat. 8, Oxford University Press, Oxford, 2007) is incorrect and further develop interpretational, computational and theoretical results which allow one to assess SB’s potential for classification and regression problems. To use SB, sequential Monte Carlo (SMC) methods are applied. As a result, it is found that SB can provide better predictions for classification problems than the corresponding boosting algorithm. A theoretical result is also given, which shows that the predictions of SB are not significantly worse than boosting, when the latter provides the best prediction. We also investigate the method on a real case study from machine learning.