Multidimensional IRT Analysis about the Subscales in the Achievement Test

Abstract

The more complicated and diverse the psychological constructs a test measures, the more sophisticated methods to study the constructs are required. Recently, multidimensional IRT is used in such studies so that the existence and structure of subscales of achievement tests are examined. The present study used the data (which had been implemented for all students in Niigata prefecture at the eighth grade level (N=9,102)) and examined in detail what the subscales measure using multidimensional IRT (bi-factor model). The results show that group factors have more impact than general factor on the 2 out of 25 items, and qualitative examination of these items confirmed the result. It is implied that multidimensional IRT can provide much item-level information compared to conventional (unidimensional) IRT and have potential for better examination of measurement constructs.