Browsing by Author "Kim, Seock-ho"
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Item A comparison of Lord's x² and Raju's area measures in detection of DIF(1993) Cohen, Allan S.; Kim, Seock-hoThe area between item response functions estimated in different samples is often used as a measure of differential item functioning (DIF). Under item response theory, this area should be 0, except for errors of measurement. This study examined the effectiveness of two statistical tests of this area—a Z test for exact signed area and a Z test for exact unsigned area—for different test length, sample size, proportion of DIF items on the test, and item parameter estimation conditions using the two-parameter model. Errors in detection made using these two statistics were compared with errors made using Lord’s Χ². Differences between all three statistics were relatively small; however, the Χ² statistic was more effective than either of the two Z tests at detecting simulated DIF. The Z test for the exact signed area was the least effective and was the most likely to result in false negative errors. Index terms: area measures, differential item functioning, item response theory, item bias, Lord’s Χ².Item A comparison of two area measures for detecting differential item functioning(1991) Kim, Seock-ho; Cohen, Allan S.The area between two item response functions is often used as a measure of differential item functioning under item response theory. This area can be measured over either an open interval (i.e., exact) or closed interval. Formulas are presented for computing the closed-interval signed and unsigned areas. Exact and closed-interval measures were estimated on data from a test with embedded items intentionally constructed to favor one group over another. No real differences in detection of these items were found between exact and closed-interval methods. Index terms: BILOG, closed interval, differential item functioning, item response functions, open interval, signed area, unsigned area.