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On the Finite-Sample Analysis of $Θ$-estimators  [PDF]
Yiyuan She
Statistics , 2015,
Abstract: In large-scale modern data analysis, first-order optimization methods are usually favored to obtain sparse estimators in high dimensions. This paper performs theoretical analysis of a class of iterative thresholding based estimators defined in this way. Oracle inequalities are built to show the nearly minimax rate optimality of such estimators under a new type of regularity conditions. Moreover, the sequence of iterates is found to be able to approach the statistical truth within the best statistical accuracy geometrically fast. Our results also reveal different benefits brought by convex and nonconvex types of shrinkage.
Dynamic adaptive multiple tests with finite sample FDR control  [PDF]
Philipp Heesen,Arnold Janssen
Statistics , 2014,
Abstract: The present paper introduces new adaptive multiple tests which rely on the estimation of the number of true null hypotheses and which control the false discovery rate (FDR) at level alpha for finite sample size. We derive exact formulas for the FDR for a large class of adaptive multiple tests which apply to a new class of testing procedures. In the following, generalized Storey estimators and weighted versions are introduced and it turns out that the corresponding adaptive step up and step down tests control the FDR. The present results also include particular dynamic adaptive step wise tests which use a data dependent weighting of the new generalized Storey estimators. In addition, a converse of the Benjamini Hochberg (1995) theorem is given. The Benjamini Hochberg (1995) test is the only "distribution free" step up test with FDR independent of the distribution of the p-values of false null hypotheses.
On the finite Sample Properties of Regularized M-estimators  [PDF]
Demian Pouzo
Mathematics , 2015,
Abstract: We propose a general framework for regularization in M-estimation problems under time dependent (absolutely regular-mixing) data which encompasses many of the existing estimators. We derive non-asymptotic concentration bounds for the regularized M-estimator. The concentration rate exhibits a "variance-bias" trade-off, with the "variance" term being governed by a novel measure of the "size" of the parameter set. We also show that the mixing structure affect the variance term by scaling the number of observations; depending on the decay rate of the mixing coefficients, this scaling can even affect the asymptotic behavior. Finally, we propose a data-driven method for choosing the tuning parameters of the regularized estimator which yield the same (up to constants) concentration bound as one that optimally balances the "(squared) bias" and "variance" terms. We illustrate the results with several canonical examples of, both, non-parametric and high-dimensional models.
Finite sample properties of power-law cross-correlations estimators  [PDF]
Ladislav Kristoufek
Quantitative Finance , 2014, DOI: 10.1016/j.physa.2014.10.068
Abstract: We study finite sample properties of estimators of power-law cross-correlations -- detrended cross-correlation analysis (DCCA), height cross-correlation analysis (HXA) and detrending moving-average cross-correlation analysis (DMCA) -- with a special focus on short-term memory bias as well as power-law coherency. Presented broad Monte Carlo simulation study focuses on different time series lengths, specific methods' parameter setting, and memory strength. We find that each method is best suited for different time series dynamics so that there is no clear winner between the three. The method selection should be then made based on observed dynamic properties of the analyzed series.
Auxiliary variables in multiple imputation in regression with missing X: a warning against including too many in small sample research  [cached]
Hardt Jochen,Herke Max,Leonhart Rainer
BMC Medical Research Methodology , 2012, DOI: 10.1186/1471-2288-12-184
Abstract: Background Multiple imputation is becoming increasingly popular. Theoretical considerations as well as simulation studies have shown that the inclusion of auxiliary variables is generally of benefit. Methods A simulation study of a linear regression with a response Y and two predictors X1 and X2 was performed on data with n = 50, 100 and 200 using complete cases or multiple imputation with 0, 10, 20, 40 and 80 auxiliary variables. Mechanisms of missingness were either 100% MCAR or 50% MAR + 50% MCAR. Auxiliary variables had low (r=.10) vs. moderate correlations (r=.50) with X’s and Y. Results The inclusion of auxiliary variables can improve a multiple imputation model. However, inclusion of too many variables leads to downward bias of regression coefficients and decreases precision. When the correlations are low, inclusion of auxiliary variables is not useful. Conclusion More research on auxiliary variables in multiple imputation should be performed. A preliminary rule of thumb could be that the ratio of variables to cases with complete data should not go below 1 : 3.
A note on multiple imputation for method of moments estimation  [PDF]
Shu Yang,Jae Kwang Kim
Statistics , 2015,
Abstract: Multiple imputation is a popular imputation method for general purpose estimation. Rubin(1987) provided an easily applicable formula for the variance estimation of multiple imputation. However, the validity of the multiple imputation inference requires the congeniality condition of Meng(1994), which is not necessarily satisfied for method of moments estimation. This paper presents the asymptotic bias of Rubin's variance estimator when the method of moments estimator is used as a complete-sample estimator in the multiple imputation procedure. A new variance estimator based on over-imputation is proposed to provide asymptotically valid inference for method of moments estimation.
Finite Sample Properties of Tests Based on Prewhitened Nonparametric Covariance Estimators  [PDF]
David Preinerstorfer
Statistics , 2014,
Abstract: We analytically investigate size and power properties of a popular family of procedures for testing linear restrictions on the coefficient vector in a linear regression model with temporally dependent errors. The tests considered are autocorrelation-corrected F-type tests based on prewhitened nonparametric covariance estimators that possibly incorporate a data-dependent bandwidth parameter, e.g., estimators as considered in Andrews and Monahan (1992), Newey and West (1994), or Rho and Shao (2013). For design matrices that are generic in a measure theoretic sense we prove that these tests either suffer from extreme size distortions or from strong power deficiencies. Despite this negative result we demonstrate that a simple adjustment procedure based on artificial regressors can often resolve this problem.
Fractional Imputation in Survey Sampling: A Comparative Review  [PDF]
Shu Yang,Jae Kwang Kim
Statistics , 2015,
Abstract: Fractional imputation (FI) is a relatively new method of imputation for handling item nonresponse in survey sampling. In FI, several imputed values with their fractional weights are created for each missing item. Each fractional weight represents the conditional probability of the imputed value given the observed data, and the parameters in the conditional probabilities are often computed by an iterative method such as EM algorithm. The underlying model for FI can be fully parametric, semiparametric, or nonparametric, depending on plausibility of assumptions and the data structure. In this paper, we give an overview of FI, introduce key ideas and methods to readers who are new to the FI literature, and highlight some new development. We also provide guidance on practical implementation of FI and valid inferential tools after imputation. We demonstrate the empirical performance of FI with respect to multiple imputation using a pseudo finite population generated from a sample in Monthly Retail Trade Survey in US Census Bureau.
A comparison of multiple imputation methods for bivariate hierarchical outcomes  [PDF]
Karla Diaz-Ordaz,Michael G. Kenward,Manuel Gomes,Richard Grieve
Statistics , 2014,
Abstract: Missing observations are common in cluster randomised trials. Approaches taken to handling such missing data include: complete case analysis, single-level multiple imputation that ignores the clustering, multiple imputation with a fixed effect for each cluster and multilevel multiple imputation. We conducted a simulation study to assess the performance of these approaches, in terms of confidence interval coverage and empirical bias in the estimated treatment effects. Missing-at-random clustered data scenarios were simulated following a full-factorial design. An Analysis of Variance was carried out to study the influence of the simulation factors on each performance measure. When the randomised treatment arm was associated with missingness, complete case analysis resulted in biased treatment effect estimates. Across all the missing data mechanisms considered, the multiple imputation methods provided estimators with negligible bias. Confidence interval coverage was generally in excess of nominal levels (up to 99.8%) following fixed-effects multiple imputation, and too low following single-level multiple imputation. Multilevel multiple imputation led to coverage levels of approximately 95% throughout. The approach to handling missing data was the most influential factor on the bias and coverage. Within each method, the most important factors were the number and size of clusters, and the intraclass correlation coefficient.
IMPUTATION USING REGRESSION ESTIMATORS FOR ESTIMATING POPULATION MEAN IN TWO-PHASE SAMPLING  [PDF]
Narendra Singh Thakur,Kalpana Yadav,Sharad Pathak
Journal of Reliability and Statistical Studies , 2012,
Abstract: This paper presents the estimation of mean in presence of missing data under two-phasesampling design using regression estimators as a tool for imputation while the size of responding( ) 1 R and non-responding ( ) 2 R group is considered as a random variable. The bias and meansquared error of suggested estimators are derived in the form of population parameters using theconcept of large sample approximation. Numerical study is performed over two populations byusing the expressions of bias and mean squared error and efficiency compared with existingestimators.
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