Sources of Differential Item Functioning between Korean and Japanese Examinees on a Second- Language Vocabulary Test
Tim Stoeckel and Phil Bennett
Miyazaki International College
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The use of item response theory in equating or creating computeradaptive
tests relies on the assumption of invariance of item parameters
across populations. This assumption can be assessed with an analysis of
differential item functioning (DIF). The purpose of this study was (a) to
ascertain whether DIF between two native language groups was present
on a 90-item multiple-choice English vocabulary test and (b) to explore
the causes of DIF, should it exist. Participants were 184 Korean and 146
Japanese undergraduate students learning English as a foreign language
in their home countries. A separate calibration t-test approach was used
to identify DIF, with the criteria set at p < 0.01 and effect size > 1 logit,
calculated as the difference in Rasch item-difficulty between the two
groups. Twenty-one items displayed DIF. The causes of DIF in nine of
those items were tentatively identified as relating to their status as
loanwords in the L1. When a tested word was a loanword in both Korean
and Japanese, differences in both the frequency and range of use of the
loanword in the two languages predicted the direction of DIF. Similarly,
phonological/orthographic overlap between two separate English loanwords
in the L1 was found to be a possible cause of DIF. Implications for
test development and further research in this area are discussed.

Stoeckel, T., & Bennett, P. (2013). Sources of differential item functioning between Korean and Japanese examinees on a second-language vocabulary test. Vocabulary Learning and Instruction, 2 (1), 47-55. doi: 10.7820/vli.v02.1.stoeckel.bennett