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Interpreting TerraNova Scores

By Inderbir Kaur Sandhu, Ph.D

Q: I am not familiar with how to interpret the test results from the TerraNova. Can you please tell me what the "average" score would be? Also, the scores are abbreviated as NP, NS, NCE, SS. Would you also please clarify what each of these mean. NP-National Percentile? SS-Standard Score? I have to look at these scores in order to decide on the correct placement level for high school students. I hope you can help.

A: Unfortunately, I am only familiar with the TerraNova based on reading and available information - I have not administered this test. I would try to help you with the information I have on NP, NS, NCE and SS.

National Percentiles (NP)
Represents the percentage of students in the national norm group whose scores fall below a given student's score. This means, a student whose NP is 72 for instance, scored higher than 72 percent of the students in the norm group. NPs scores are useful for comparing local student achievement to students' achievement at the national level.

National Stanine (NS)
A scale that divides the scores of the norming sample into nine groups ranging from a high of 9 to a low of 1. Stanines are normalised scores that have a constant relationship to Percentiles. That is, a given Percentile always falls into the same Stanine. Stanine 5, for example, always includes Percentiles 41-59. Stanines are single digit scores and are not likely to be confused with percentage of items answered correctly, and they can be averaged because they are equal interval scores. However, Stanines provide less detail about student performance than other derived scores because they categorise test performance into only nine broad units.

Normal Curve Equivalent (NCE)
This curve was designed to be used in the evaluation of compensatory education and other special programmes. The range is from 1 to 99 and coincide with the NP scale at 1, 50, and 99. NCEs are normalised equal interval scores and are not recommended for use in reporting individual student scores since the NCE is easily confused with the NP.

Scale Scores (SS)
The Scale Score is the basic score for TerraNova and other CTB assessments. It is used to derive all the other scores that describe test performance. Scale Scores can be obtained by one of two scoring methods. The first is Item Response Theory (IRT) item-pattern scoring, a procedure offered only by CTB among the major K-12 test publishers. With item-pattern scoring, Scale Scores are derived numerically using all the information contained in a student's pattern of item responses. The second method is number correct scoring. This method converts the number of correct responses (or points earned for constructed-response items) to a Scale Score. For groups of 25 or more students, the item-pattern and number-correct Scale Scores produce equivalent results. Customers can choose to use either scoring method. CTB recommends item-pattern scoring because it provides more accurate results for individual students. Scale Scores are equal-interval scores that can be averaged and used in other statistical analyses.

A very informative site for information on interpretation of the scores can be found here: Guide to Test Interpretation: The Alaska Norm-Referenced Test

Hope that helps!


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