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ERIC Number: EJ1010165
Record Type: Journal
Publication Date: 2013-Apr
Pages: 19
Abstractor: As Provided
ISBN: N/A
ISSN: ISSN-0013-1644
Item Purification Does Not Always Improve DIF Detection: A Counterexample with Angoff's Delta Plot
Magis, David; Facon, Bruno
Educational and Psychological Measurement, v73 n2 p293-311 Apr 2013
Item purification is an iterative process that is often advocated as improving the identification of items affected by differential item functioning (DIF). With test-score-based DIF detection methods, item purification iteratively removes the items currently flagged as DIF from the test scores to get purified sets of items, unaffected by DIF. The purpose of this article is to highlight that item purification is not always useful and that a single run of the DIF method may return equally suitable results. Angoff's Delta plot is considered as a counterexample DIF method, with a recent improvement to the derivation of the classification threshold. Several possible item purification processes may be defined with this method, and all of them are compared through a simulation study and a real data set analysis. It appears that none of these purification processes clearly improves the Delta plot performance. A tentative explanation is drawn from the conceptual difference between the modified Delta plot and the other traditional DIF methods. (Contains 4 figures and 1 table.)
SAGE Publications. 2455 Teller Road, Thousand Oaks, CA 91320. Tel: 800-818-7243; Tel: 805-499-9774; Fax: 800-583-2665; e-mail: journals@sagepub.com; Web site: http://sagepub.com
Publication Type: Journal Articles; Reports - Research
Education Level: Early Childhood Education; Preschool Education; Kindergarten; Primary Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A
Identifiers - Assessments and Surveys: Boehm Test of Basic Concepts