| 1. |
- Christle, David J., et al.
(författare)
-
Isolated electron spins in silicon carbide with millisecond coherence times
- 2015
-
Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 14:2, s. 160-163
-
Tidskriftsartikel (refereegranskat)abstract
- The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries(1). Nonetheless, because certain SiC defects have electronic states with sharp optical and spin transitions, they are increasingly recognized as a platform for quantum information and nanoscale sensing(2-16). Here, we show that individual electron spins in high-purity monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects(2,3), these states exhibit exceptionally long ensemble Hahn-echo spin coherence times, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route towards wafer-scale quantum technologies.
|
|
| 2. |
- Andrich, David, et al.
(författare)
-
Real and artificial differential item functioning
- 2012
-
Ingår i: Journal of educational and behavioral statistics. - : American Educational Research Association (AERA). - 1076-9986 .- 1935-1054. ; 37:3, s. 387-416
-
Tidskriftsartikel (refereegranskat)abstract
- The literature in modern test theory on procedures for identifying items with differential item functioning (DIF) among two groups of persons includes the Mantel–Haenszel (MH) procedure. Generally, it is not recognized explicitly that if there is real DIF in some items which favor one group, then as an artifact of this procedure, artificial DIF that favors the other group is induced in the other items. Using the Rasch model for dichotomous responses as a theoretical basis, this article proves that the source of artificial DIF in the MH procedure is that estimates of the person locations are substituted for their unknown values. The article then demonstrates that the formalization of artificial DIF implies mathematically (a) a particular sequential, iterative procedure for detecting items with real DIF and for identifying a set of items that may have no DIF and (b) a resolution of the items with real DIF for quantifying the DIF on the same metric as the items showing no DIF and provides expected value curves and tests of fit for the item for each of the groups. Finally, because the source of artificial DIF in the MH procedure is the substitution of a parameter with its estimate, it is suggested that all procedures that use the substitution of an estimate for a parameter are likely to induce artificial DIF.
|
|
| 3. |
- Andrich, David, et al.
(författare)
-
Real and Artificial Differential Item Functioning in Polytomous Items
- 2015
-
Ingår i: Educational and Psychological Measurement. - SAGE Publications : SAGE Publications. - 0013-1644 .- 1552-3888. ; 75:2, s. 185-207
-
Tidskriftsartikel (refereegranskat)abstract
- Differential item functioning (DIF) for an item between two groups is present if, for the same person location on a variable, persons from different groups have different expected values for their responses. Applying only to dichotomously scored items in the popular Mantel–Haenszel (MH) method for detecting DIF in which persons are classified by their total scores on an instrument, Andrich and Hagquist articulated the concept of artificial DIF and showed that as an artifact of the MH method, real DIF in one item favoring one group inevitably induces artificial DIF favoring the other group in all other items. Using the dichotomous Rasch model in which the total score for a person is a sufficient statistic, and therefore justifies classifying persons by their total scores, Andrich and Hagquist showed that to distinguish between real and artificial DIF in an item identified by the MH method, a sequential procedure for resolving items is implied. Using the polytomous Rasch model, this article generalizes the concept of artificial DIF to polytomous items, in which multiple item parameters play a role. The article shows that the same principle of resolving items sequentially as with dichotomous items applies also to distinguishing between real and artificial DIF with polytomous items. A real example and a small simulated example that parallels the real example are used illustratively.
|
|
| 4. |
- Hagquist, Curt, 1952-, et al.
(författare)
-
Determinants of artificial DIF : a study based on simulated polytomous data
- 2015
-
Ingår i: Psychological Test and Assessment Modeling. - Germany : Pabst Science Publishers. - 2190-0493 .- 2190-0507. ; 57:3, s. 342-376
-
Tidskriftsartikel (refereegranskat)abstract
- A general problem in DIF analyses is that some items favouring one group can induce the appear-ance of DIF in others favouring the other group. Artificial DIF is used as a concept for describing and explaining that kind of DIF which is an artefact of the procedure for identifying DIF, con-trasting it to real DIF which is inherent to an item. The purpose of this paper is to elucidate how real both uniform and non-uniform DIF, referenced to the expected value curve, induce artificial DIF, how this DIF impacts on the person parameter estimates and how different factors affect real and artificial DIF, in particular the alignment of person and item locations. The results show that the same basic principles apply to non-uniform DIF as to uniform DIF, but that the effects on person measurement are less pronounced in non-uniform DIF. Similar to artifi-cial DIF induced by real uniform DIF, the size of artificial DIF is determined by the magnitude of the real non-uniform DIF. In addition, in both uniform and non-uniform DIF, the magnitude of artificial DIF depends on the location of the items relative to the distribution of the persons. In contrast to uniform DIF, the direction of non-uniform real DIF (e.g. favouring one group or the other) is affected by the location of the items relative to the distribution of the persons.The results of the simulation study also confirm that regardless of type of DIF, in the person estimates, artifi-cial DIF never balances out real DIF.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
- Hagquist, Curt, 1952-, et al.
(författare)
-
Measuring subjective health among adolescents in Sweden : A Rasch-analysis of the HBSC-instrument
- 2004
-
Ingår i: Social Indicators Research. - : Kluwer Academic Publishers. - 0303-8300 .- 1573-0921. ; 68:2, s. 201-220
-
Tidskriftsartikel (refereegranskat)abstract
- The cross-national WHO-study Health Behaviourin School-Aged Children (HBSC) is acomprehensive adolescent survey ongoing inEurope based on a public health perspective.The present study, examining theHBSC-instrument on subjective health, uses theunidimensional Rasch model. Items are analysedwith respect to their operating characteristicsacross the whole range of the subjective healthscale and the empirical operation of theresponse categories intended to be ordered forall items. The study is based oncross-sectional data collected in Sweden duringthe 1980s and 1990s among students in yearsfive, seven and nine.The analyses reveal that the symptom checklistin the HBSC-instrument does not workconsistently with the Rasch model when alleight items are analysed simultaneously. Inparticular, the response categories do not workas intended. Hence, the original set of eightitems should not be used to construct a latentmeasure of subjective health. In order tobring the instrument to meet the requirementsof the Rasch model, three items were removed. The reduced set of five items did workconsistently with the model with respect to theresponse categories, and did show relativeinvariance across the latent trait. Since a fewof the remaining items showed lack ofinvariance across genders and grades thatproblem should be solved, if the reduced itemset is to be used for post-hoc analyses.Furthermore, the analysis of the reduced set ofitems suggests that both ``somatic'' and``psychological'' complaints might be consideredas parts of one higher order dimension ofsubjective health.In order to improve the questionnaire, furtherattention should be paid to the response formatof the items.
|
|
| 8. |
- Hagquist, Curt, 1952-, et al.
(författare)
-
Recent advances in analysis of differential item functioning in health research using the Rasch model
- 2017
-
Ingår i: Health and Quality of Life Outcomes. - : Springer. - 1477-7525. ; 15, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Rasch analysis with a focus on Differential Item Functioning (DIF) is increasingly used for examination of psychometric properties of health outcome measures. To take account of DIF in order to retain precision of measurement, split of DIF-items into separate sample specific items has become a frequently used technique. The purpose of the paper is to present and summarise recent advances of analysis of DIF in a unified methodology. In particular, the paper focuses on the use of analysis of variance (ANOVA) as a method to simultaneously detect uniform and non-uniform DIF, the need to distinguish between real and artificial DIF and the trade-off between reliability and validity. An illustrative example from health research is used to demonstrate how DIF, in this case between genders, can be identified, quantified and under specific circumstances accounted for using the Rasch model.Methods: Rasch analyses of DIF were conducted of a composite measure of psychosomatic problems using Swedish data from the Health Behaviour in School-aged Children study for grade 9 students collected during the 1985–2014 time periods.Results: The procedures demonstrate how DIF can be identified efficiently by ANOVA of residuals, and how the magnitude of DIF can be quantified and potentially accounted for by resolving items according to identifiable groups and using principles of test equating on the resolved items. The results of the analysis also show that the real DIF in some items does affect person measurement estimates.Conclusions: Firstly, in order to distinguish between real and artificial DIF, the items showing DIF initially should not be resolved simultaneously but sequentially. Secondly, while resolving instead of deleting a DIF item may retain reliability, both options may affect the content validity negatively. Resolving items with DIF is not justified if the source of the DIF is relevant for the content of the variable; then resolving DIF may deteriorate the validity of the instrument. Generally, decisions on resolving items to deal with DIF should also rely on external information.
|
|
