Summarizing Item Difficulty Variation with Parcel Scores

• Published in: Journal of educational measurement Vol. 45; no. 4; pp. 363 - 389
• Main Authors: Camilli, Gregory, Prowker, Adam, Dossey, John A., Lindquist, Mary M., Chiu, Ting-Wei, Vargas, Sadako, De La Torre, Jimmy
• Format: Journal Article
• Language: English
• Published: Malden, USA Blackwell Publishing Inc 01.12.2008; Wiley Subscription Services; Blackwell Publishing; Wiley Subscription Services, Inc
• Subjects: Academic achievement; Aggregation; Computation; Correlations; Difficulty Level; Educational evaluation; Educational tests & measurements; Evaluation Methods; Grade 4; Item difficulty; Jurisdiction; Mathematical growth; Mathematics; Mathematics education; Multilevel models; National assessment; National Competency Tests; Rasch model; Scores; Statistical variance; Statistics; Strength; Test Bias; Test Items
• ISSN: 0022-0655; 1745-3984
• DOI: 10.1111/j.1745-3984.2008.00070.x

A new method for analyzing differential item functioning is proposed to investigate the relative strengths and weaknesses of multiple groups of examinees. Accordingly, the notion of a conditional measure of difference between two groups (Reference and Focal) is generalized to a conditional variance. The objective of this article is to present and illustrate a strategy for aggregating results across sets of similar items that exhibit item difficulty variation. Logically, this aggregation strategy is related to the idea of DIF amplification, but estimation is ultimately carried out in the framework of a confirmatory multidimensional Rasch model. Grade 4 data from the 2000 National Assessment of Educational Progress are used to illustrate the technique.