Evaluating the consistency and accuracy of proficiency classifications using item response theory.

As demanded by the No Child Left Behind (NCLB) legislation, state-mandated testing has increased dramatically, and almost all of these tests report examinee\u27s performance in terms of several ordered proficiency categories. Like licensure exams, these assessments often have high-stakes consequences, such as graduation requirements and school accountability. It goes without saying that we want these tests to be of high quality, and the quality of these test instruments can be assessed, in part, through the decision accuracy (DA) and decision consistency (DC) indices. With the popularization of IRT, an increasing number of tests are adopting IRT for test development, test score equating and all other data analyses, which naturally calls for approaches to evaluating DA and DC in the framework of IRT. However, it is still common to observe the practice of carrying out all data analyses in IRT while reporting DA and DC indices derived in the framework of CTT. This situation testifies to the necessity to the exploration of possibilities to quantify DA and DC under IRT. The current project addressed several possible methods for estimating DA and DC in the framework of IRT with the specific focus on tests involving both dichotomous and polytomous items. It consisted of several simulation studies in which the all IRT methods introduced were valuated with simulated data, and all methods introduced were also be applied in a real data context to demonstrate their application in practice. Overall, the results from this study provided evidence that would support the use of the 3 IRT methods introduced in this project in estimating DA and DC indices in most of the simulated situations, and in most of the cases the 3 IRT methods produced results that were close to the true DA and DC values, and consistent results to (sometimes even better results than) those from the commonly used L&L method. It seems the IRT methods showed more robustness on the distribution shapes than on the test length. Their implications to educational measurement and some directions for future studies in this area were also discussed

1′,3′,4′,5′,7′,8′-Hexafluoro-1,1′′,2,2′′,3,3′′,4,4′′-octa­phenyl-2′,6′-dihydro­dispiro­[cyclo­penta-1,3-diene-5,2′-naphthalene-6′,5′′-cyclo­penta-1′′,3′′-diene] dichloro­methane monosolvate

The mol­ecule of the title compound, C66H40F6·CH2Cl2, is centrosymmetric; the dihedral angle between the central fluorinated unit and the cyclo­penta­diene ring is 88.36 (7)°. The dihedral angles between the cyclo­penta­diene ring and the four surrounding phenyl rings are in the range 26.6 (1)–65.6 (1)°. Centrosymmetric cavities in the crystal structure are populated by disordered dichloro­methane solvent mol­ecules

Self-cancellation of ephemeral regions in the quiet Sun

With the observations from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, we statistically investigate the ephemeral regions (ERs) in the quiet Sun. We find that there are two types of ERs: normal ERs (NERs) and self-cancelled ERs (SERs). Each NER emerges and grows with separation of its opposite polarity patches which will cancel or coalesce with other surrounding magnetic flux. Each SER also emerges and grows and its dipolar patches separate at first, but a part of magnetic flux of the SER will move together and cancel gradually, which is described with the term "self-cancellation" by us. We identify 2988 ERs among which there are 190 SERs, about 6.4% of the ERs. The mean value of self-cancellation fraction of SERs is 62.5%, and the total self-cancelled flux of SERs is 9.8% of the total ER flux. Our results also reveal that the higher the ER magnetic flux is, (i) the easier the performance of ER self-cancellation is, (ii) the smaller the self-cancellation fraction is, and (iii) the more the self-cancelled flux is. We think that the self-cancellation of SERs is caused by the submergence of magnetic loops connecting the dipolar patches, without magnetic energy release.Comment: 6 pages, 4 figures, accepted for publication in ApJ