arXiv subjects

Giorgio E. Montanari

Publications and source records attributed to Giorgio E. Montanari.

6 recordsLinked to original sources

arXiv2026

Modeling within-department homogeneity in research quality rankings: an application to the Italian ISPD

In this paper, we consider the academic department ranking system of Italy, which is based on a performance index named Indice Standardizzato di Performance Dipartimentale (ISPD). While critiques to the ISPD have been moved for its marked tendency to polarization, we here formalize a yet unexplored determinant of this phenomenon, that is, the presence of within-department homogeneity among the standardized scores used to build the index. We account for this intra-departmental correlation by modeling it as a function of departments' size. The proposed model, estimated via Maximum Likelihood, allows to build a fairer ranking procedure via the definition of a properly adjusted version of the ISPD. The estimation framework is also adapted to fit publicly available data, which are coarsened by rounding and/or left-truncated. To this end, a novel probability distribution termed Betoidal is introduced. Empirical evidence in favor of the proposed model is found in the 2017 and 2022 data. Moreover, a simulation study shows that the adjusted index significantly overcomes not only the original ISPD, but also other more data-demanding competing proposals.

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arXiv2014

Item selection by Latent Class-based methods

The evaluation of nursing homes is usually based on the administration of questionnaires made of a large number of polytomous items. In such a context, the Latent Class (LC) model represents a useful tool for clustering subjects in homogenous groups corresponding to different degrees of impairment of the health conditions. It is known that the performance of model-based clustering and the accuracy of the choice of the number of latent classes may be affected by the presence of irrelevant or noise variables. In this paper, we show the application of an item selection algorithm to real data collected within a project, named ULISSE, on the quality-of-life of elderly patients hosted in italian nursing homes. This algorithm, which is closely related to that proposed by Dean and Raftery in 2010, is aimed at finding the subset of items which provides the best clustering according to the Bayesian Information Criterion. At the same time, it allows us to select the optimal number of latent classes. Given the complexity of the ULISSE study, we perform a validation of the results by means of a sensitivity analysis to different specifications of the initial subset of items and of a resampling procedure.

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arXiv2014

Three-step estimation of latent Markov models with covariates

We propose a modified version of the three-step estimation method for the latent class model with covariates, which may be used to estimate latent Markov models for longitudinal data. The three-step estimation approach we propose is based on a preliminary clustering of sample units on the basis of the time specific responses only. This approach represents an useful estimation tool when a large number of response variables are observed at each time occasion. In such a context, full maximum likelihood estimation, which is typically based on the Expectation-Maximization algorithm, may have some drawbacks, essentially due to the presence of many local maxima of the model likelihood. Moreover, the EM algorithm may be particularly slow to converge, and may become unstable with complex LM models. We prove the consistency of the proposed three-step estimator when the number of response variables tends to infinity. We also show the results of a simulation study aimed at evaluating the performance of the proposed alternative approach with respect to the full likelihood method. We finally illustrate an application to a real dataset on the health status of elderly people hosted in Italian nursing homes.

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arXiv2012

A hierarchical latent class model for predicting disability small area counts from survey data

This article considers the estimation of the number of severely disabled people using data from the Italian survey on Health Conditions and Appeal to Medicare. Disability is indirectly measured using a set of categorical items, which survey a set of functions concerning the ability of a person to accomplish everyday tasks. Latent Class Models can be employed to classify the population according to different levels of a latent variable connected with disability. The survey, however, is designed to provide reliable estimates at the level of Administrative Regions (NUTS2 level), while local authorities are interested in quantifying the amount of population that belongs to each latent class at a sub-regional level. Therefore, small area estimation techniques should be used. The challenge of the present application is that the variable of interest is not directly observed. Adopting a full Bayesian approach, we base small area estimation on a Latent Class model in which the probability of belonging to each latent class changes with covariates and the influence of age is learnt from the data using penalized splines. Deimmler-Reisch bases are shown to improve speed and mixing of MCMC chains used to simulate posteriors.

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arXiv2010

An investigation of the discriminant power and dimensionality of items used for assessing health condition of elderly people

With reference to the questionnaire adopted within the Italian project "Ulisse" to assess health condition of elderly people, we investigate two important issues: discriminant power and actual number of dimensions measured by the items composing the questionnaire. The adopted statistical approach is based on the joint use of the latent class model and a multidimensional item response theory model based on the 2PL parametrization. The latter allows us to account for the different discriminant power of these items. The analysis is based on the data collected on a sample of 1699 elderly people hosted in 37 nursing homes in Italy. This analysis shows that the selected items indeed measure a different number of dimensions of the health status and that they considerably differ in terms of discriminant power (effectiveness in measuring the actual health status). Implications for the assessment of the performance of nursing homes from a policy-maker prospective are discussed.

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arXiv2009

Latent Markov model for longitudinal binary data: An application to the performance evaluation of nursing homes

Performance evaluation of nursing homes is usually accomplished by the repeated administration of questionnaires aimed at measuring the health status of the patients during their period of residence in the nursing home. We illustrate how a latent Markov model with covariates may effectively be used for the analysis of data collected in this way. This model relies on a not directly observable Markov process, whose states represent different levels of the health status. For the maximum likelihood estimation of the model we apply an EM algorithm implemented by means of certain recursions taken from the literature on hidden Markov chains. Of particular interest is the estimation of the effect of each nursing home on the probability of transition between the latent states. We show how the estimates of these effects may be used to construct a set of scores which allows us to rank these facilities in terms of their efficacy in taking care of the health conditions of their patients. The method is used within an application based on data concerning a set of nursing homes located in the Region of Umbria, Italy, which were followed for the period 2003--2005.

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