Item Response Theory, Vertical Scaling, and Something's Awry in the State of Test Mark
Titel:
Item Response Theory, Vertical Scaling, and Something's Awry in the State of Test Mark
Auteur:
Clemans, William V.
Verschenen in:
Educational assessment
Paginering:
Jaargang 1 (1993) nr. 4 pagina's 329-347
Jaar:
1993-10-01
Inhoud:
It is generally accepted that variability in performance will increase throughout Grades 1 to 12. Those with minimal knowledge of a domain should vary but little, but, as learning rates differ, variability should increase as a function of growth. In this article, the series of reading tests from a widely used test battery for Grades 1 through 12 was singled out for study as the scale scores for the series have the opposite characteristic-that is, variability is greatest at Grade 1 and decreases as growth proceeds. Item response theory (IRT) scaling was used; in previous editions, the publisher had used Thurstonian scaling and the variance increased with growth. Using data with known characteristics (i.e., weight distributions for ages 6 through 17), a comparison was made between the effectiveness of IRT and Thurstonian scaling procedures. The Thurstonian scaling more accurately reproduced the characteristics of the known distributions. As IRT scaling was shown to improve when perfect scores were included in the analyses and when items were selected whose difficulties reflected the entire range of ability, these steps were recommended. However, even when these steps were implemented with IRT, the Thurstonian scaling was still found to be more accurate.
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