The Proximal Bootstrap for Finite-Dimensional Regularized Estimators

We propose a proximal bootstrap that can consistently estimate the limiting distribution of sqrt(n)-consistent estimators with nonstandardasymptotic distributions in a computationally efficient manner by formulating the proximal bootstrap estimator as the solution to aconvex optimization problem, which can have a closed-form solution for certain designs. This paper considers the application to finite-dimensionalregularized estimators, such as the lasso, l1-norm regularized quantile regression, l1-norm support vector regression, and trace regression via nuclear norm regularization.

msreg: A command for consistent estimation of linear regression models using matched data

Economists often use matched samples, especially when dealing with earning data where some observations are missing in one sample and need to be imputed from another sample. Hirukawa and Prokhorov (2018, Journal of Econometrics 203: 344–358) show that the ordinary least-squares estimator using matched samples is inconsistent and propose two consistent estimators. We describe a new command, msreg, that implements these two consistent estimators based on two samples. The estimators attain the parametric convergence rate if the number of continuous matching variables is no greater than four.

On quantile based co-risk measures and their estimation

Conditional Value-at-Risk (CoVaR) is defined as the Value-at-Risk of a certain risk given that the related risk equals a given threshold (CoVaR=) or is smaller/larger than a given threshold (CoVaR</CoVaR≥). We extend the notion of Conditional Value-at-Risk to quantile based co-risk measures that are weighted mixtures of CoVaR at different levels and hence involve the stochastic dependence that occurs among the risks and that is captured by copulas. We show that every quantile based co-risk measure is a quantile based risk measure and hence fulfills all related properties. We further discuss continuity results of quantile based co-risk measures from which consistent estimators for CoVaR< and CoVaR≥ based risk measures immediately follow when plugging in empirical copulas. Although estimating co-risk measures based on CoVaR= is a nontrivial endeavour since conditioning on events with zero probability is necessary we show that working with so-called empirical checkerboard copulas allows to construct strongly consistent estimators for CoVaR= and related co-risk measures under very mild regularity conditions. A small simulation study illustrates the performance of the obtained estimators for special classes of copulas.

Comparing Two Treatments in Two Period Repeated Measurement Design

This work deals with nonparametric test procedures for comparing effects of two treatments in two period parallel group design, where each subject receives the same treatment over the two periods. The procedures are based on consistent estimators of relative treatment effects in each period and that of covariate adjusted effects with responses in period 1 as covariates. Related asymptotic results are obtained followed by necessary simulation studies to evaluate the performance of the tests. AMS 2010 subject classifications: 62G10 62J15

A Falsifiability Characterization of Double Robustness Through Logical Operators

We address the characterization of problems in which a consistent estimator exists in a union of two models, also termed as a doubly robust estimator. Such estimators are important in missing information, including causal inference problems. Existing characterizations, based on the semiparametric theory of projections, have seen sufficient progress, but can still leave one’s understanding less than satisfied as to when and especially why such estimation works. We explore here a different, explanatory characterization – an exegesis based on logical operators. We show that double robustness exists if and only if we can produce consistent estimators for each contributing model based on an “AND” estimator, i. e., an estimator whose consistency generally needs both models to be correct. We show how this characterization explains double robustness through falsifiability.

A New Method for Logistic Model Assessment

It is well known that the logistic model plays an important role for the analysis of binary outcomes. Most of the existing methods for the assessment of logistic models are constructed based on the distance between the observed and the predicted outcomes. We consider a new method from a different perspective by assessing the distance between two consistent estimators developed under the same logistic model form. The proposed tests are easy to implement and are applicable to both prospective and case-control studies.