# What is the difference between growth index and conditional growth index?

Document created by Community User on Aug 1, 2016Last modified by Community User on Jun 6, 2017
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What is the difference between growth index and conditional growth index?

The growth index is how many RIT points a student grew above or below their growth projection. So if a student's starting RIT score is 200, and their ending RIT score is 212, they grew 12 RIT points. If their growth projection was 7, then their growth was 5 more than their projection, so their growth index is 5. You can calculate a student's growth index using this formula: Growth Index = Observed Growth - Projected Growth.

While the growth index is a useful number and easy to understand, it is not appropriate for making growth comparisons of students in different grades or subjects. For example, we tend to see larger RIT gains in primary grades than in high school. So a growth index of 5, for example, may not mean exactly the same thing for a kindergartner and a 10th grader.

The conditional growth index (CGI) expresses a student's growth in terms of standard deviations above or below the mean (average). This is also known as a z-score or standard score. By converting the student's growth into standard deviations from the mean, we can directly compare the CGIs for students in different grades or subjects. You can calculate a student's conditional growth index using this formula: Conditional Growth Index = Growth Index ÷ Standard Deviation of Normative Growth.