Magnitude Of Misfit Research Articles

Performance of the S 2 Statistic for the Multidimensional Graded Response Model.

is a popular item fit index that is available in commercial software packages such as flexMIRT. However, no research has systematically examined the performance of for detecting item misfit within the context of the multidimensional graded response model (MGRM). The primary goal of this study was to evaluate the performance of under two practical misfit scenarios: first, all items are misfitting due to model misspecification, and second, a small subset of items violate the underlying assumptions of the MGRM. Simulation studies showed that caution should be exercised when reporting item fit results of polytomous items using within the context of the MGRM, because of its inflated false positive rates (FPRs), especially with a small sample size and a long test. performed well when detecting overall model misfit as well as item misfit for a small subset of items when the ordinality assumption was violated. However, under a number of conditions of model misspecification or items violating the homogeneous discrimination assumption, even though true positive rates (TPRs) of were high when a small sample size was coupled with a long test, the inflated FPRs were generally directly related to increasing TPRs. There was also a suggestion that performance of was affected by the magnitude of misfit within an item. There was no evidence that FPRs for fitting items were exacerbated by the presence of a small percentage of misfitting items among them.

Using Bayesian Nonparametric Item Response Function Estimation to Check Parametric Model Fit.

Previous studies indicated that the assumption of logistic form of parametric item response functions (IRFs) is violated often enough to be worth checking. Using nonparametric item response theory (IRT) estimation methods with the posterior predictive model checking method can obtain significance probabilities of fit statistics in a Bayesian framework by accounting for the uncertainty of the parameter estimation and can indicate the location and magnitude of misfit for an item. The purpose of this study is to check the performance of the Bayesian nonparametric method to assess the IRF fit of parametric IRT models for mixed-format tests and compare it with the existing bootstrapping nonparametric method under various conditions. The simulation study results show that the Bayesian nonparametric method can detect misfit items with higher power and lower type I error rates when the sample size is large and with lower type I error rates compared with the bootstrapping method for the conditions with nonmonotonic items. In the real-data study, several dichotomous and polytomous misfit items were identified and the location and magnitude of misfit were indicated.

Using the Bootstrap Method to Evaluate the Critical Range of Misfit for Polytomous Rasch Fit Statistics.

The purpose of this study was to apply the bootstrap procedure to evaluate how the bootstrapped confidence intervals (CIs) for polytomous Rasch fit statistics might differ according to sample sizes and test lengths in comparison with the rule-of-thumb critical value of misfit. A total of 25 simulated data sets were generated to fit the Rasch measurement and then a total of 1,000 replications were conducted to compute the bootstrapped CIs under each of 25 testing conditions. The results showed that rule-of-thumb critical values for assessing the magnitude of misfit were not applicable because the infit and outfit mean square error statistics showed different magnitudes of variability over testing conditions and the standardized fit statistics did not exactly follow the standard normal distribution. Further, they also do not share the same critical range for the item and person misfit. Based on the results of the study, the bootstrapped CIs can be used to identify misfitting items or persons as they offer a reasonable alternative solution, especially when the distributions of the infit and outfit statistics are not well known and depend on sample size.

An Assessment of the Nonparametric Approach for Evaluating the Fit of Item Response Models

As item response theory has been more widely applied, investigating the fit of a parametric model becomes an important part of the measurement process. There is a lack of promising solutions to the detection of model misfit in IRT. Douglas and Cohen introduced a general nonparametric approach, RISE (Root Integrated Squared Error), for detecting model misfit. The purposes of this study were to extend the use of RISE to more general and comprehensive applications by manipulating a variety of factors (e.g., test length, sample size, IRT models, ability distribution). The results from the simulation study demonstrated that RISE outperformed G2 and S‐X2 in that it controlled Type I error rates and provided adequate power under the studied conditions. In the empirical study, RISE detected reasonable numbers of misfitting items compared to G2 and S‐X2, and RISE gave a much clearer picture of the location and magnitude of misfit for each misfitting item. In addition, there was no practical consequence to classification before and after replacement of misfitting items detected by three fit statistics.

Modeling of misfit induced defects in Co/Cr recording media

A 2D model to study the effect of crystal orientation on interfacial structural misfit and Co grain defect density for hcp Co/bcc Cr thin film system has been introduced. The magnitude of misfit depends strongly on the Co/Cr orientation, their respective lattice parameters, the grain size and to a lesser extend, the relative lattice orientation across the interface. However, the modeling results showed that by introducing lattice defects such as fcc stacking faults and misfit dislocations in the Co layer, one can greatly reduce this misfit and relax the interface.

Stress relaxation and misfit dislocation nucleation in the growth of misfitting films: A molecular dynamics simulation study

The low-temperature growth and relaxation of misfitting films are analyzed on the basis of two-dimensional molecular dynamics simulations using Lennard–Jones potentials. The temporal evolution of the surface morphology and the mechanisms for misfit dislocation nucleation and stress relaxation are monitored. Pseudomorphic film growth is observed up to a critical thickness. In some cases, the formation of voids within the film relaxes some of the stress. At the critical thickness, dislocations nucleate and relax most of the misfit. The critical thickness increases with decreasing lattice mismatch and depends on the sign of the misfit. The critical thickness of compressively strained films is smaller than that of films with the same magnitude of misfit, but in tension. The mechanism of dislocation nucleation is different in tension and compression and, in all cases, is associated with the roughness of the film surface. In the compressive misfit case, dislocations nucleate by squeezing-out an atom at the base of surface depressions. In the tensile misfit case, however, the nucleation of misfit dislocations involves the concerted motion of a relatively large number of atoms, leading to insertion of an extra lattice (plane) row into an already continuous film. These results show that the critical thickness depends intimately on the film morphology which, in turn, is determined as an integral part of the film growth process.

The precision of fit at the implant prosthodontic interface

Statement of problem. Percussion, visual observation, and conventional periapical radiographs are the methods most frequently used clinically to evaluate the accuracy of implant component assemblies, whereas methods to measure the precision of fit are limited. Purpose. In this study the Periotest instrument was used to evaluate the stability of the interfaces between the implant and the abutment, along with the abutment and the gold cylinder under a series of assembly conditions. The hypothesis tested is that a more negative Periotest value (PTV) would indicate an accurate fit and a more positive value PTV would correlate with an inaccurate fit. Material and methods. To investigate this hypothesis in vitro, two bovine ribs were used as patient simulation models. Each model contained three self-tapping Brånemark implants placed approximately 7 to 10 mm apart and arranged in a reasonable curvature. A series of component assembly conditions were created as accurate and inaccurate with thickness gauges of 25.4 μm, 50.8 μm, and 101.6 μm. Results. The mean Periotest values and SDs for accurately assembled abutments and gold cylinders were 6.0 ± 0.32 and 3.4 ± 0.68, respectively. Periotest value data of the assembly conditions were statistically analyzed with multiple regression analysis. The misfit in the implant to abutment interface resulted in a more negative Periotest value trend ( r = 0.54) with increases in gauge thickness. However, the same magnitudes of misfit at the abutment to gold cylinder interface produced a more positive Periotest value trend ( r = 0.72). Conclusion. The PTV trends were consistent with increased stability at the abutment to implant interface from the increasing magnitude of misfit created with the thickness gauges. In contrast, the measurement trends observed for the abutment to gold cylinder interface were consistent with decreased stability with each increase in gauge thickness inserted at the interface. (J Prosthet Dent 1997;77:497-502.)

γ′-Ni<SUB>3</SUB>(Al, Ti)L1<SUB>2</SUB>型規則相中への不規則γ相の析出

Optimum alloy compositions and heat treatments to obtain fine dispersion of disordered γ particles in an L12 ordered γ′-Ni3(Al, Ti), and the morphology change of γ precipitates during aging have been investigated by means of transmission electron microscopy.A uniform solid solution of γ′-L12 ordered phase supersaturated with Ni can be obtained by solution annealing in a suitable temperature range. The γ′ phase hardens appreciably by the fine precipitation of disordered γ. The shape of γ precipitates formed during aging is initially spherical or round-cubic and grow into platelets as aging proceeds. High resolution electron microscopy revealed that the γ precipitates are perfectly coherent with the matrix γ′ as long as the γ-precipitates are plates. The loss of coherency initiates by the introduction of dislocations at the γ⁄γ′ interface followed by the step formation at the dislocations. The γ precipitates become grobular after the loss of coherency.The chemical compositions of the matrix and the precipitates have been determined by means of EDS microanalysis in an analytical electron microscope. The sense and magnitude of misfit between the γ′ matrix and γ precipitates are determined from the spacings of misfit dislocations and the chemical compositions of γ and γ′ phases.

愛媛県上須戒鉱山産セクター構造を示す含マンガンエジリンオージャイト

Sector-zoned manganoan aegirine-augites from the Kamisugai mine, Ehime Prefecture, have been investigated by an optical microscopy and an electron probe microanalyser. Sector-zoned crystal elongates along c-axis and is composed of the {100} and {010} sectors. The cores of the {100} sectors are rich in johannsenite and diopside molecules, while the rims become poorer in johannsenite molecule. The cores of the {010} sectores are rich in acmite and diopside molecules, and the rims become richer in acmite molecule. These zonal structures of each sector are discussed in reference to the crystallization temperature and oxygen fugacity in particular. These factors control the solubilities of johannsenite and diopside molecules to acmite molecule. The sectoral fractionation of the molecules during crystallization can be explained by the difference of the lattice energies of each molecule and that of the magnitude of misfit between Si-O tetrahedron and M-O polyhedron in the structure.