ERIC Number: ED476147
Record Type: Non-Journal
Publication Date: 2003-Apr
Reference Count: N/A
Using DIF Dissection To Assess Effects of Item Deletion Due to DIF on the Performance of SAT I: Reasoning Test Sub-populations.
Zhang, Yanling; Matthews-Lopez, Joy; Dorans, Neil J.
Statistical procedures for detecting differential item functioning (DIF) are often used to screen items for construct irrelevant variance. Standard DIF detection procedures focus on only one categorical variables at an aggregated group or one-way level, like gender or ethnicity/race. Building on previous work by P. Hu and N. Dorans (1998), N. Dorans and P. Holland (1993), and Y. Zhang (2001), this study applied a DIF dissection classification scheme to SAT:I Verbal data. Subsequently, the effect of deleting sizable DIF items on reported scores after equipercentile re-equating were explored using data from a spring administration of the SAT for 9,517 test takers in 10 subgroups. By using a "dissection" approach to reference and focal group formations, this two-way classification scheme may yield new and detailed insight into item functioning at the subgroup level. Two hypotheses were studied: (1) whether or not the deletion of sizeable DIF items disadvantageous to a particular subgroup will affect that subgroup the most; and (2) whether or not the effects of item deletion on scores can be predicted by the standardization method. Both hypotheses were predicted by the results of this research. Scaled score differences following item deletion and re-equating varied among subgroups, depending on the DIF effects. Subgroups disadvantaged by the subsequently deleted sizable DIF items gained scaled score points whereas advantaged groups lost. Regression analyses confirmed the second hypothesis. It was also shown that by deleting an item with sizable negative DIF, the focal group might be greatly benefited. Among three item deletion scenarios, DIF effects yielded from the two-way classification scheme showed very little interaction in the majority of cases. (Contains 3 figures, 14 tables, and 15 references.) (Author/SLD)
Publication Type: Reports - Research; Speeches/Meeting Papers
Education Level: N/A
Authoring Institution: Educational Testing Service, Princeton, NJ.