Roberta Varriale

Systemic vascular dysregulation and retrobulbar hemodynamics in normal-tension glaucoma.

PURPOSE To investigate the influence of systemic vascular dysregulation on retrobulbar hemodynamics in normal-tension glaucoma (NTG). METHODS Forty-four untreated patients with NTG and 40 healthy controls matched for age, sex, and intraocular pressure were included. Cold-induced nailfold capillaroscopic features, mean and diastolic ocular perfusion pressures (mOPP, dOPP), endothelin-1 (ET-1) and nitric oxide markers, as nitrates (NO(2)), plasma values were recorded. Peak-systolic velocity, end-diastolic velocity (EDV), and resistivity index (RI) were measured in the ophthalmic artery (OA), short posterior ciliary arteries, and the central retinal artery by color Doppler imaging. Differences between groups were determined by Students t-test. Relationships among ET-1, NO(2), OPPs, and retrobulbar hemodynamics were assessed using correlation and multiple linear regression analyses. RESULTS Altered capillaroscopy was more frequent (72.7% vs. 5.0%, P < 0.001), mOPP and dOPP values were lower (44.54 ± 2.81 vs. 52.18 ± 4.47 mm Hg; 57.89 ± 4.30 vs. 68.28 ± 6.91 mm Hg; P < 0.001), and ET-1 and NO(2) values were respectively higher and lower (1.62 ± 0.22 vs. 1.12 ± 0.20 pg/mL and 142.17 ± 14.34 vs. 231.30 ± 6.16 μmol/mg prot; P < 0.001) in patients than the same values in controls. EDV was lower and RI higher in OA (5.87 ± 1.17 vs. 11.41 ± 2.30 cm/s; 0.76 ± 0.03 vs. 0.64 ± 0.03; P < 0.001) in subjects with NTG than in controls. In patients RI-OA was positively related to ET-1 (t = 2.704, P = 0.010) and negatively related to NO(2) (t = -4.477, P < 0.001). CONCLUSIONS Impaired retrobulbar hemodynamics may proceed from a vascular endotheliopathy in patients with NTG.

Robust ANalysis Of VAriance: An approach based on the Forward Search

A simple robust method for the detection of atypical observations and the analysis of their effect in the ANOVA framework is presented. It is proposed to use a forward search procedure that orders the observations by their closeness to the hypothesized model. The procedure can be applied following two different strategies: one that adds units maintaining the relative group dimension and the other that adds only one new unit at each step of the search. The assessment of the goodness of the method is carried out through a simulation study. The method is then applied to real data. Results are presented through easy to interpret plots which are powerful in revealing the structure of the data.

Multilevel mixture factor models for the evaluation of educational programs’ effectiveness

Factor models aim at explaining the associations among observed random variables in terms of fewer unobserved random variables, called common factors. When data have a hierarchical structure, multilevel mixture factor models are a powerful and flexible tool useful to correctly take into account the correlation between first-level units due to the data structure, and to evaluate the presence of latent sub-populations of units with some typical profile at different levels of the analysis.

Robust Random Effects Models: A Diagnostic Approach Based on the Forward Search

This paper presents a robust procedure for the detection of atypical observations and for the analysis of their effect on model inference in random effects models. Given that the observations can be outlying at different levels of the analysis, we focus on the evaluation of the effect of both first and second level outliers and, in particular, on their effect on the higher level variance which is statistically evaluated with the Likelihood-Ratio Test. A cut-off point separating the outliers from the other observations is identified through a graphical analysis of the information collected at each step of the Forward Search procedure; the Robust Forward LRT is the value of the classical LRT statistic at the cut-off point.

The Effectiveness of University Education: A Structural Equation Model

The evaluation of the effectiveness of higher education is a crucial aspect of competitiveness of modern economies. In this contribution we investigate the quality and effectiveness of higher education in Italy using a structural equation model; in particular, we evaluate the performance of the university system from the users’ point of view, both immediately following (internal effectiveness), and one year after (external effectiveness), the completion of the degree. The model allows the construction of synthetic indexes and hence the ranking of study programs.