Malvina Vamvakari

Repeatability of dietary patterns extracted through multivariate statistical methods: a literature review in methodological issues

Abstract In the last few years, the need for processing large amount of data in nutrition science was dramatically arose. This created the need to apply, primarily, advanced analytical research methods that could enable researchers to handle the large amount of information. Dietary pattern analysis is a commonly used approach to enable and incorporate this phenomenon in nutrition research. This article reviews the most common dietary pattern’s assessment statistical methods, evaluating at the same time the up-to-day knowledge regarding the reliability and validity of the retrieved patterns. The review is based on both a-priori (diet scores) and a-posteriori (multivariate statistical analysis) methods. The reports from the existing few studies suggest that the use of both a-priori and a-posteriori pattern analyses in nutrition surveys should be made with consciousness. The suggestion of new statistical techniques for the control of repeatability of dietary patterns is considered essential.

Adult student assessment in second chance schools in Greece: teachers’ views

The present study aims at presenting the views of second chance school (SCS) teachers, seconded from formal education schools. Firstly, on the positive outcomes resulting from project and portfolio assessment and student self evaluation in SCSs, secondly, the difficulties experienced during the assessment process and, thirdly, the combined use of descriptive and numerical assessment in SCSs. Two hundred and seventeen teachers, working in SCSs in Greece, filled in questionnaires with 21 close‐ended questions, and provided relevant information. Data elaboration and statistical analysis were performed. Factor analysis was used to pinpoint the main factors that influence the attitude of teachers towards assessment in SCSs. The results of the survey showed, among others, that teachers, in principle, express a positive attitude towards the above‐mentioned forms of assessment, but they find it difficult to cope firstly, with the students’ poor understanding of assessment purposes, criteria and description terminology; secondly, with the lack of an officially organized plan/list of proposed projects and forms of different assessment techniques; and thirdly, with student stigmatization caused by numerical grades. In the discussion section suggestions have been put forward to enhance adult students’ understanding, to boost teachers’ official support during assessment procedures and, finally, to reform assessment methods implemented in formal education, so that assessment becomes more stimulating, credible, integrated and fair for all students, adult and non‐adult ones.

Investigating the role of orthogonal and non – orthogonal rotation in multivariate factor analysis, in regard to the repeatability of the extracted factors: A simulation study

ABSTRACT Factor analysis (FA) is the most commonly used pattern recognition methodology in social and health research. A technique that may help to better retrieve true information from FA is the rotation of the information axes. The main goal is to test the reliability of the results derived through FA and to reveal the best rotation method under various scenarios. Based on the results of the simulations, it was observed that when applying non-orthogonal rotation, the results were more repeatable as compared to the orthogonal rotation, and, when no rotation was applied.

A q-random walk approximated by a q-Brownian motion

Abstract Consider a sequence of independent q-Bernoulli trials with odds of success geometrically decreasing with rate q, 0 q 1 . In this work, we introduce the process generated by making a step to the right when the outcome of the ith q-Bernoulli trial is “success” and a step to the left otherwise, for i = 1 , 2 , … , n . Furhtermore, the ith q-Bernoulli trial, happens during the ith part of a suitable defined partition of the time period ( 0 , t ] , i = 1 , 2 , … , n . The position X n , q ( t ) at time t of this process defines a q-random walk. Also, asymptotically, as n → ∞ , by a q-analogue of the De Moivre-Laplace theorem, we approximate this q-random walk by a q-Brownian motion. This q-Brownian motion is the continuous analogue of the q-random walk process and is distributed according to a linear transformed standardized Stieltjes-Wigert distribution.

The use of components’ weights improves the diagnostic accuracy of a health-related index

ABSTRACT This work aims to evaluate whether the use of specific weights in each component of a health-related index, is associated with its diagnostic accuracy. In addition, the impact of a composite health-related indexs components multitude is examined in relation to its classification ability. An un-weighted and various weighted indices were constructed using different weighting methods. The indices’ diagnostic ability was evaluated by using true positive rate, true negative rate, true rate, positive predictive value, negative predictive value and the area under the receiver operating characteristic curve. Weights used in this study were obtained from linear discriminant analysis and binary logistic regression. These indices were applied in both simulated and actual data; and a variety of scenarios was applied based on the distributions parameters of the component variables and on the number of components used. Results indicate that weighted indices’ evaluation measures were significantly higher compared to the un-weighted one; whereas area under receiver operating characteristic curve was positively associated with the number of components of each index that were correlated with the outcome. Weighting of indexs components, as well as greater number of components related to the investigated outcome should be recommended for the construction of accurate indices.