The Change-Sensitive Score (CSS), as the name implies, is an Item Response Theory (IRT)-based score metric that is useful for monitoring longitudinal change. The CSS is derived from the examinee’s raw score on the test and does not rely on comparison to the examinee’s age-based reference group. Therefore, it is sensitive to actual changes in the underlying ability or trait. The adjusted scores simply provide a rank-ordering in a reference group of peers, whereas the CSS tells whether actual growth or decline happened. CSS is independent of the performance of the reference group.
As an example, an individual might show a 4-point gain in CSS over a period of 1 year between Time 1 and Time 2, but if their reference peer group showed a 5-point gain, the individual would actually have a lower adjusted score at Time 2 than Time 1, which would mask the underlying growth.
Although the CSS is not a norm-referenced score, it is useful to have a common origin across measures for consistency.