Premium
An NCME Instructional Module on Using Differential Step Functioning to Refine the Analysis of DIF in Polytomous Items
Author(s) -
Penfield Randall D.,
Gattamorta Karina,
Childs Ruth A.
Publication year - 2009
Publication title -
educational measurement: issues and practice
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.158
H-Index - 52
eISSN - 1745-3992
pISSN - 0731-1745
DOI - 10.1111/j.1745-3992.2009.01135.x
Subject(s) - polytomous rasch model , differential item functioning , item response theory , rasch model , psychology , task (project management) , differential (mechanical device) , statistics , test (biology) , computer science , cognitive psychology , psychometrics , mathematics , paleontology , management , engineering , economics , biology , aerospace engineering
Traditional methods for examining differential item functioning (DIF) in polytomously scored test items yield a single item‐level index of DIF and thus provide no information concerning which score levels are implicated in the DIF effect. To address this limitation of DIF methodology, the framework of differential step functioning (DSF) has recently been proposed, whereby measurement invariance is examined within each step underlying the polytomous response variable. The examination of DSF can provide valuable information concerning the nature of the DIF effect (i.e., is the DIF an item‐level effect or an effect isolated to specific score levels), the location of the DIF effect (i.e., precisely which score levels are manifesting the DIF effect), and the potential causes of a DIF effect (i.e., what properties of the item stem or task are potentially biasing). This article presents a didactic overview of the DSF framework and provides specific guidance and recommendations on how DSF can be used to enhance the examination of DIF in polytomous items. An example with real testing data is presented to illustrate the comprehensive information provided by a DSF analysis.