# What is the RIT scale?

Document created by Community User on Jul 29, 2016Last modified by Community User on Apr 17, 2019
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What is the RIT Scale?

NWEA’s RIT scale stands for Rasch Unit scale. There are several RIT scales: one each for reading, language usage, mathematics, and general science plus a few scales that are under development.

## What are the characteristics of the RIT scales?

These RIT scales are stable, equal interval scales that use individual item difficulty values to measure student achievement independent of grade level (that is, across grades). "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. "Stable" means that the scores on the same scale from different students, or from the same students at different times, can be directly compared, even though different sets of test items are administered. A RIT score also has the same meaning regardless of the grade or age of the student.

In summary, the RIT scale is:
• An achievement scale
• Accurate
• Equal interval
• Useful for measuring growth over time
• The same regardless of the grade or age of the student
See also: How can I explain RIT scores to students and parents?

## How was the RIT scale developed?

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.

## What does a particular RIT score mean?

A RIT score measures a student's level of achievement in a particular subject. If a student has a particular RIT score, this means that the student is about 50% likely to correctly answer an item calibrated at that RIT level, and therefore topics at this RIT level are likely to be topics the student is ready to learn, or are in the student's zone of proximal development. NWEA provides reports like the Learning Continuum and Student Profile that will show you what topics the student's RIT score suggests they are ready to learn.

NWEA reports also contain normative data from our norms study. You can find the percentile ranking for a particular RIT score on most reports, allowing you to compare a student's RIT score with other students in the same grade and subject.

For additional information about the RIT scale and norms, see: Normative Data & RIT Scores.

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1884