M.A.P. and Measurement Scale - RIT
The RIT Scale
The RIT Scale is a curriculum scale that uses individual item difficulty values to estimate student achievement. An advantage of the RIT scale is that it can relate the numbers on the scale directly to the difficulty of items on the tests. In addition, the RIT scale is an equal interval scale. Equal interval means that the difference between scores is the same regardless of whether a student is at the top, bottom, or middle of the RIT scale, and it has the same meaning regardless of grade level.
RIT scales, like scales underlying most educational tests, are built from data about the performance of individual examinees on individual items. The theory governing scale construction is called Item Response Theory (IRT). NWEA uses a specific IRT model conceived by Danish mathematician, Georg Rasch, (1901-1980). Rasch is best known for his contributions to psychometrics, and his model is used extensively in assessment in education, particularly for skill attainment and cognitive assessments.
Characteristics of the RIT Scale include:
It is an achievement scale.
It is an accurate scale
t is an equal interval scale.
It helps to measure growth over time.
It has the same meaning regardless of grade or age of the student.