An Empirical Investigation of Thurstone and IRT Methods of Scaling Achievement Tests

The purpose of this study was to investigate the nature and characteristics of the measurement scales developed using Thurstone and item response theory (IRT) methods of scaling achievement tests for the same set of data. Expanded standard score scales were created using Thurstone, one‐parameter IRT, and three‐parameter IRT models, and descriptive information on achievement growth and variability was obtained for examinees in Grades 9 through 12 in the subject areas of vocabulary, reading, and mathematics. The results indicated increasing variability in all three test areas for all three scaling methods as grade level increased. In addition, greater average growth across grades was observed at the 90th percentile as compared to the 10th percentile, even with the IRT‐based scales.