Assessing the effectiveness of a sthocastic regression imputation method for ordered categorical data

The main aim of this paper is to describe a workable method based on stochastic regression and multiple imputation analysis (MISR) to recover for missingness in surveys where multi-item Likert-type scale are used to measure a latent attribute (namely, the quality of university teaching). A simulation analysis has been carried out and results have been compared in terms of bias and efficiency with other missing data handling methods, specifically: Complete Cases Analysis (CCA) and Multiple Imputation by Chained Equations (MICE). The authors provide also functions (implemented in R language) to apply the procedure to a matrix of ordered categorical items. Functions described allow: (i) to simulate missing data at random and completely at random; (ii) to replicate the simulation study presented in this work in order to assess the accuracy in distribution and in estimation of a multiple imputation procedure

Handling missing data in item response theory. Assessing the accuracy of a multiple imputation procedure based on latent class analysis

A critical issue in analyzing multi-item scales is missing data treatment. Previous studies on this topic in the framework of item response theory have shown that imputation procedures are in general associated with more accurate estimates of item location and discrimination parameters under several missing data generating mechanisms. This paper proposes a model-based multiple imputation procedure for multiple categorical items (dichotomous, multinomial or Likert-type) which relies on the results of latent class analysis to impute missing item responses. The effectiveness of the proposed technique is assessed in the estimation of item response theory parameters using a range of ad hoc measures. The accuracy of the method is assessed with respect to other single and multiple imputation procedures, under different missing data generating mechanisms and different rate of missingness (5% to 30%). The simulation results indicate that the proposed technique performs satisfactorily under all conditions and has the greatest potential with severe rates of missingness and under non ignorable missing data mechanisms. The method was implemented in R code with a function that calls scripts from a latent class analysis routine

Differences of cultural capitol among students in transition to university some first survey evidences

The role played by ‘Cultural Capital’ is crucial in shaping students’ decisions with respect to the school university transition. This work is based on an ad hoc survey carried out on a sample of students enrolled in 2006 in the University of Cagliari. The ‘cultural capital’ is a latent variable which students are supposed to possess at a greater or lesser degree. It has been here operationalized in four sub-components: (i) built-up by activities made by students themselves; (ii) built up by activities made by students’ parents; (iii) transmitted by students’ parents; (iv) built-up by formal education experiences. Each sub-component has been evaluated via students’ responses to a battery of items in a questionnaire. Latent Class Analysis has been adopted in order to provide non arbitrary scaling of some of the sub-components and to sort out mutually exclusive classes of students, characterized by a different intensity of the latent variable. Moreover, Item Response Models have been used to assess the calibration of the questionnaire as an instrument to measure the cultural capital of the targeted population

Ulteriori proposte per la determinazione di indicatori di inefficienza dell'attività formativa dell'Università

Evaluation is one of the major tasks for managing the Italian University system. One of the evaluation parameters has to do with the efficiency/inefficiency of the university in pursuing one of its main goals: graduation of the students. Inefficiency could be seen with respect to three different components: (a) students quitting before the end of the legal length of their studies, (b) students quitting in a period that is the double of the legal length of the studies, (c) students that do not terminate their studies in time. The aim of the present paper is to propose some indicators that can be fruitfully used in a joint evaluation of these components. Some simulations are also provided

Domanda di istruzione universitaria in Sardegna da parte degli studenti delle scuole secondarie

Col presente lavoro si cercherà di offrire alcuni spunti di riflessione sui problemi dell’efficienza e dell’efficacia del sistema universitario principalmente attraverso uno studio sull’intenzione di accedere all’istruzione universitaria espressa da un insieme di studenti dell’ultimo anno delle scuole medie superiori. Si farà, cioè, riferimento a quella che comunemente viene indicata come la domanda potenziale di istruzione universitaria. Il lavoro è articolato in due parti, nella prima vengono illustrate le dinamiche evolutive, a partire dagli anni Cinquanta, della citata domanda di istruzione con riferimento all’università italiana in generale ed agli atenei sardi in particolare. Nella seconda, la domanda di istruzione universitaria viene analizzata attraverso un’indagine condotta sugli studenti delle scuole medie superiori di tre province sarde: viene descritto l’insieme dei rispondenti utilizzato per l’analisi della stessa e viene presentato un modello logit a risposta politomica attraverso il quale, considerando alcuni predittori quali il sesso e la scuola di provenienza, è stata modellata la variabile dipendente a tre modalità (Sì, Non so, No), relativa al quesito posto agli studenti delle scuole medie “Intendi proseguire gli studi dopo il diploma di maturità?”

Structural and Functional Characterization of a New Double Variant Haemoglobin (HbG-Philadelphia/Duarte α268Asn→Lysβ262Ala→Pro)

We report the first case of cosegregation of two haemoglobins (Hbs): HbG-Philadelphia [α68(E17)Asn → Lys] and HbDuarte [β62(E6)Ala → Pro]. The proband is a young patient heterozygous also for β°-thalassaemia. We detected exclusively two haemoglobin variants: HbDuarte and HbG-Philadelphia/Duarte. Functional study of the new double variant HbG-Philadelphia/Duarte exhibited an increase in oxygen affinity, with a slight decrease of cooperativity and Bohr effect. This functional behaviour is attributed to β62Ala → Pro instead of α68Asn → Lys substitution. Indeed, HbG-Philadelphia isolated in our laboratory from blood cells donor carrier for this variant is not affected by any functional modification, whereas purified Hb Duarte showed functional properties very similar to the double variant. NMR and MD simulation studies confirmed that the presence of Pro instead of Ala at the β62 position produces displacement of the E helix and modifications of the tertiary structure. The substitution α68(E17)Asn → Lys does not cause significant structural and dynamical modifications of the protein. A possible structure-based rational of substitution effects is suggested

Genome-wide association study of susceptibility loci for breast cancer in Sardinian population

Abstract Background Despite progress in identifying genes associated with breast cancer, many more risk loci exist. Genome-wide association analyses in genetically-homogeneous populations, such as that of Sardinia (Italy), could represent an additional approach to detect low penetrance alleles. Methods We performed a genome-wide association study comparing 1431 Sardinian patients with non-familial, BRCA1/2-mutation-negative breast cancer to 2171 healthy Sardinian blood donors. DNA was genotyped using GeneChip Human Mapping 500 K Arrays or Genome-Wide Human SNP Arrays 6.0. To increase genomic coverage, genotypes of additional SNPs were imputed using data from HapMap Phase II. After quality control filtering of genotype data, 1367 cases (9 men) and 1658 controls (1156 men) were analyzed on a total of 2,067,645 SNPs. Results Overall, 33 genomic regions (67 candidate SNPs) were associated with breast cancer risk at the p < 10−6 level. Twenty of these regions contained defined genes, including one already associated with breast cancer risk: TOX3. With a lower threshold for preliminary significance to p < 10−5, we identified 11 additional SNPs in FGFR2, a well-established breast cancer-associated gene. Ten candidate SNPs were selected, excluding those already associated with breast cancer, for technical validation as well as replication in 1668 samples from the same population. Only SNP rs345299, located in intron 1 of VAV3, remained suggestively associated (p-value, 1.16x10−5), but it did not associate with breast cancer risk in pooled data from two large, mixed-population cohorts. Conclusions This study indicated the role of TOX3 and FGFR2 as breast cancer susceptibility genes in BRCA1/2-wild-type breast cancer patients from Sardinian population

Genome-wide association study of susceptibility loci for breast cancer in Sardinian population.

BACKGROUND: Despite progress in identifying genes associated with breast cancer, many more risk loci exist. Genome-wide association analyses in genetically-homogeneous populations, such as that of Sardinia (Italy), could represent an additional approach to detect low penetrance alleles. METHODS: We performed a genome-wide association study comparing 1431 Sardinian patients with non-familial, BRCA1/2-mutation-negative breast cancer to 2171 healthy Sardinian blood donors. DNA was genotyped using GeneChip Human Mapping 500 K Arrays or Genome-Wide Human SNP Arrays 6.0. To increase genomic coverage, genotypes of additional SNPs were imputed using data from HapMap Phase II. After quality control filtering of genotype data, 1367 cases (9 men) and 1658 controls (1156 men) were analyzed on a total of 2,067,645 SNPs. RESULTS: Overall, 33 genomic regions (67 candidate SNPs) were associated with breast cancer risk at the p <  0(-6) level. Twenty of these regions contained defined genes, including one already associated with breast cancer risk: TOX3. With a lower threshold for preliminary significance to p < 10(-5), we identified 11 additional SNPs in FGFR2, a well-established breast cancer-associated gene. Ten candidate SNPs were selected, excluding those already associated with breast cancer, for technical validation as well as replication in 1668 samples from the same population. Only SNP rs345299, located in intron 1 of VAV3, remained suggestively associated (p-value, 1.16 x 10(-5)), but it did not associate with breast cancer risk in pooled data from two large, mixed-population cohorts. CONCLUSIONS: This study indicated the role of TOX3 and FGFR2 as breast cancer susceptibility genes in BRCA1/2-wild-type breast cancer patients from Sardinian population