arXiv subjects

Silvia Polettini

Publications and source records attributed to Silvia Polettini.

3 recordsLinked to original sources

arXiv2018

A unit-level small area model with misclassified covariates

Small area models are mixed effects regression models that link the small areas and borrow strength from similar domains. When the auxiliary variables used in the models are measured with error, small area estimators that ignore the measurement error may be worse than direct estimators. Alternative small area estimators accounting for measurement error have been proposed in the literature but only for continuous auxiliary variables. Adopting a Bayesian approach, we extend the unit-level model in order to account for measurement error in both continuous and categorical covariates. For the discrete variables we model the misclassification probabilities and estimate them jointly with all the unknown model parameters. We test our model through a simulation study exploring different scenarios. The impact of the proposed model is emphasized through application to data from the Ethiopia Demographic and Health Survey where we focus on the women's malnutrition issue, a dramatic problem in developing countries and an important indicator of the socio-economic progress of a country.

stat.ME↗

arXiv2018

Assessing Bayesian Nonparametric Log-Linear Models: an application to Disclosure Risk estimation

We present a method for identification of models with good predictive performances in the family of Bayesian log-linear mixed models with Dirichlet process random effects. Such a problem arises in many different applications; here we consider it in the context of disclosure risk estimation, an increasingly relevant issue raised by the increasing demand for data collected under a pledge of confidentiality. Two different criteria are proposed and jointly used via a two-stage selection procedure, in a M-open view. The first stage is devoted to identifying a path of search; then, at the second, a small number of nonparametric models is evaluated through an application-specific score based Bayesian information criterion. We test our method on a variety of contingency tables based on microdata samples from the US Census Bureau and the Italian National Security Administration, treated here as populations, and carefully discuss its features. This leads us to a journey around different forms and sources of bias along which we show that (i) while based on the so called "score+search" paradigm, our method is by construction well protected from the selection-induced bias, and (ii) models with good performances are invariably characterized by an extraordinarily simple structure of fixed effects. The complexity of model selection - a very challenging and difficult task in a strictly parametric context with large and sparse tables - is therefore significantly defused by our approach. An attractive collateral result of our analysis are fruitful new ideas about modeling in small area estimation problems, where interest is in total counts over cells with a small number of observations.

stat.ME↗

arXiv2015

Bayesian nonparametric disclosure risk estimation via mixed effects log-linear models

Statistical agencies and other institutions collect data under the promise to protect the confidentiality of respondents. When releasing microdata samples, the risk that records can be identified must be assessed. To this aim, a widely adopted approach is to isolate categorical variables key to the identification and analyze multi-way contingency tables of such variables. Common disclosure risk measures focus on sample unique cells in these tables and adopt parametric log-linear models as the standard statistical tools for the problem. Such models often have to deal with large and extremely sparse tables that pose a number of challenges to risk estimation. This paper proposes to overcome these problems by studying nonparametric alternatives based on Dirichlet process random effects. The main finding is that the inclusion of such random effects allows us to reduce considerably the number of fixed effects required to achieve reliable risk estimates. This is studied on applications to real data, suggesting, in particular, that our mixed models with main effects only produce roughly equivalent estimates compared to the all two-way interactions models, and are effective in defusing potential shortcomings of traditional log-linear models. This paper adopts a fully Bayesian approach that accounts for all sources of uncertainty, including that about the population frequencies, and supplies unconditional (posterior) variances and credible intervals.

stat.AP↗