Papers by Leonardo Grilli
Journal of the American Statistical Association, Jun 1, 2011
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International Federation of Classification Societies, 2015
We propose a multidimensional latent class IRT model for the analysis of ordinal responses subjec... more We propose a multidimensional latent class IRT model for the analysis of ordinal responses subject to nonignorable missingness. The missingness mechanism is driven by 2 sets of latent classes summarizing, respectively, the propensity to respond and the abilities measured by the test items. The model allows for both item covariates and examinee covariates and it is fitted by the EM algorithm. The model is illustrated through an application to university student careers, focusing on the grades of first-year exams, where the missingness of a grade is likely to be nonignorable.
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The paper analyzes the performance of university students, with reference to first-year compulsor... more The paper analyzes the performance of university students, with reference to first-year compulsory courses. We propose an Item Response Theory model that includes two latent variables corresponding to the student’s ability and the preference about the order of attempted exams. In this way, we explicitly account for nonignorable missing observations since the indicators of item response also contribute to measure the ability and then the model is of within-item multidimensional type. The two latent variables are assumed to have a discrete distribution defining latent classes of students that are homogenous in terms of ability and priority assigned to exams.
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The European Journal of Public Health, 2016
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In the last years several methods for the analysis of ordinal multivariate multilevel data have b... more In the last years several methods for the analysis of ordinal multivariate multilevel data have been proposed (Muthén, 1994; Rabe-Hesketh et al., 2001; Mazzolli, 2001; Lillard and Panis 2000). The present paper highlights the interpretation of the variance-covariance parameters of the assumed multivariate distribution of the latent variables. Moreover, under the hypothesis of a multivariate Gaussian distribution, the paper illustrates some alternative specifications of the model, which have been proposed in order to use certain estimation ...
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Social Science Research Network, 2016
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European journal of public health, Oct 15, 2016
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Metron-International Journal of Statistics, Dec 1, 2010
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arXiv (Cornell University), Jan 4, 2021
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arXiv (Cornell University), Sep 21, 2016
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48th Scientific Meeting of the Italian Statistical Society, Apr 29, 2016
The paper analyzes the performance of university students, with reference to first-year compulsor... more The paper analyzes the performance of university students, with reference to first-year compulsory courses. We propose an Item Response Theory model that includes two latent variables corresponding to the student’s ability and the preference about the order of attempted exams. In this way, we explicitly account for nonignorable missing observations since the indicators of item response also contribute to measure the ability and then the model is of within-item multidimensional type. The two latent variables are assumed to have a discrete distribution defining latent classes of students that are homogenous in terms of ability and priority assigned to exams.
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Quality & Quantity, Jan 30, 2023
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Statistical Methods and Applications, Apr 16, 2019
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Statistical Methods & Applications
The extension of quantile regression to count data raises several issues. We compare the traditio... more The extension of quantile regression to count data raises several issues. We compare the traditional approach, based on transforming the count variable using jittering, with a recently proposed approach in which the coefficients of quantile regression are modelled by parametric functions. We exploit both methods to analyse university students’ data to evaluate the effect of emergency remote teaching due to COVID-19 on the number of credits earned by the students. The coefficients modelling approach performs a smoothing that is especially convenient in the tails of the distribution, preventing abrupt changes in the point estimates and increasing precision. Nonetheless, model selection is challenging because of the wide range of options and the limited availability of diagnostic tools. Thus the jittering approach remains fundamental to guide the choice of the parametric functions.
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arXiv (Cornell University), Jan 4, 2021
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Papers by Leonardo Grilli