Calibration estimation in dual-frame surveys

Survey statisticians make use of auxiliary information to improve estimates. One important example is calibration estimation, which constructs new weights that match benchmark constraints on auxiliary variables while remaining “close” to the design weights. Multiple-frame surveys are increasingly used by statistical agencies and private organizations to reduce sampling costs and/or avoid frame undercoverage errors. Several ways of combining estimates derived from such frames have been proposed elsewhere; in this paper, we extend the calibration paradigm, previously used for single-frame surveys, to calculate the total value of a variable of interest in a dual-frame survey. Calibration is a general tool that allows to include auxiliary information from two frames. It also incorporates, as a special case, certain dual-frame estimators that have been proposed previously. The theoretical properties of our class of estimators are derived and discussed, and simulation studies conducted to compare the efficiency of the procedure, using different sets of auxiliary variables. Finally, the proposed methodology is applied to real data obtained from the Barometer of Culture of Andalusia survey.     

A Mixed Model-assisted Regression Estimator that Uses Variables Employed at the Design Stage

The Generalized regression estimator (GREG) of a finite population mean or total has been shown to be asymptotically optimal when the working linear regression model upon which it is based includes variables related to the sampling design. In this paper a regression estimator assisted by a linear mixed superpopulation model is proposed. It accounts for the extra information coming from the design in the random component of the model and saves degrees of freedom in finite sample estimation. This procedure combines the larger asymptotic efficiency of the optimal estimator and the greater finite sample stability of the GREG. Design based properties of the proposed estimator are discussed and a small simulation study is conducted to explore its finite sample performance.     

Modelling spatio-temporal air pollution data from a mobile monitoring station

ABSTRACT

Environmental data is typically indexed in space and time. This work deals with modelling spatio-temporal air quality data, when multiple measurements are available for each space-time point. Typically this situation arises when different measurements referring to several response variables are observed in each space-time point, for example, different pollutants or size resolved data on particular matter. Nonetheless, such a kind of data also arises when using a mobile monitoring station moving along a path for a certain period of time. In this case, each spatio-temporal point has a number of measurements referring to the response variable observed several times over different locations in a close neighbourhood of the space-time point. We deal with this type of data within a hierarchical Bayesian framework, in which observed measurements are modelled in the first stage of the hierarchy, while the unobserved spatio-temporal process is considered in the following stages. The final model is very flexible and includes autoregressive terms in time, different structures for the variance-covariance matrix of the errors, and can manage covariates available at different space-time resolutions. This approach is motivated by the availability of data on urban pollution dynamics: fast measures of gases and size resolved particulate matter have been collected using an Optical Particle Counter located on a cabin of a public conveyance that moves on a monorail on a line transect of a town. Urban microclimate information is also available and included in the model. Simulation studies are conducted to evaluate the performance of the proposed model over existing alternatives that do not model data over the first stage of the hierarchy.     

Bayesian model comparison based on expected posterior priors for discrete decomposable graphical models

The implementation of the Bayesian paradigm to model comparison can be problematic. In particular, prior distributions on the parameter space of each candidate model require special care. While it is well known that improper priors cannot be routinely used for Bayesian model comparison, we claim that also the use of proper conventional priors under each model should be regarded as suspicious, especially when comparing models having different dimensions. The basic idea is that priors should not be assigned separately under each model; rather they should be related across models, in order to acquire some degree of compatibility, and thus allow fairer and more robust comparisons. In this connection, the intrinsic prior as well as the expected posterior prior (EPP) methodology represent a useful tool. In this paper we develop a procedure based on EPP to perform Bayesian model comparison for discrete undirected decomposable graphical models, although our method could be adapted to deal also with directed acyclic graph models. We present two possible approaches. One based on imaginary data, and one which makes use of a limited number of actual data. The methodology is illustrated through the analysis of a 2×3×4 contingency table.     

Ownership and control in local public utilities: the Italian case

The paper discusses the ownership and control structures of local public utilities by showing evidence from the Italian case. In this discussion, the focus is on three main aspects: the ownership structure, the board composition and independence, and citizens’ involvement (service charters). The main results from this study reveal that there are controversial aspects, which need further investigation. The existence of a principal–principal conflict is clearly arising from an in-depth analysis of the ownership structures. In addition, the board of directors, because of the lack of actual independence, does not seem to be a useful arena to manage and solve these conflicts. Other governance mechanisms are thus needed, to increase accountability to citizens. Within this, service charters seem to be a useful tool to protect the “public interest”. However, service charters content analysis suggests that further implementation actions are due. The paper contributes to the debate on conflicts of interests and governance mechanisms in local public utilities suggesting possible developments of agency theory and discussing implications for further research.     

Latent variable modeling of disability in people aged 65 or more

This paper aims at classifying, on the basis of their disability profile, the population of elderly and quantifying the number of those with a very low level of functioning in a central region of Italy. This is accomplished using a set of variables on the difficulty of accomplishing everyday tasks (Activities of Daily Living, ADL) and functions. This issue is very important for National and Local Health organizations in order to evaluate the need for care, planning services, elaborating policies and allocating resources. Latent class models are applied on data coming from the Italian National Survey on Health Conditions and Appeal to Medicare to extract the latent trait of disability and classify the elder population according to their disability profile. Model selection brings to a classification into four latent classes. Looking at posterior probabilities, classes may be interpreted as follows: elderly without disability, with difficulties in movements, with difficulties in movements and daily tasks, with very low functioning level. Estimates of the amount of population aged 65 or more falling in each class is also provided. Cross-validation shows evidence of the robustness of such classification. Item response theory models are also applied to the items considered to study how functions are lost with increasing levels of disability. In particular, the abilities of climbing stairs and stooping down are those lost first, while those of eating and getting washed are those lost last.