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Two New Statistics to Detect Answer Copying
Author(s) -
Sotaridona Leonardo S.,
Meijer Rob R.
Publication year - 2003
Publication title -
journal of educational measurement
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.917
H-Index - 47
eISSN - 1745-3984
pISSN - 0022-0655
DOI - 10.1111/j.1745-3984.2003.tb01096.x
Subject(s) - copying , statistics , computer science , psychology , mathematics education , econometrics , mathematics , political science , law
Two new indices to detect answer copying on a multiple‐choice test—S 1 and S 2 —were proposed. The S 1 index is similar to the K index (Holland, 1996) and the K 2 index (Sotaridona & Meijer, 2002) but the distribution of the number of matching incorrect answers of the source and the copier is modeled by the Poisson distribution instead of the binomial distribution to improve the detection rate of K and K 2 . The S 2 index was proposed to overcome a limitation of the K and K 2 index, namely, their insensitiveness to correct answers copying. The S 2 index incorporates the matching correct answers in addition to the matching incorrect answers. A simulation study was conducted to investigate the usefulness of S 1 and S 2 for 40‐ and 80‐item tests, 100 and 500 sample sizes, and 10%, 20%, 30%, and 40% answer copying. The Type I errors and detection rates of S 1 and S 2 were compared with those of the K 2 and the ω copying index (Wollack, 1997). Results showed that all four indices were able to maintain their Type I errors, with S 1 and K 2 being slightly conservative compared to S 2 and ω. Furthermore, S 1 had higher detection rates than K 2 . The S 2 index showed a significant improvement in detection rate compared to K and K 2 .