How to Compare Test Scores

When counselors and psychologists report test scores, they often report one of the scores found in the table below. When several tests are used, it is helpful to know how the scores compare from one test to another.

A good place to begin is to locate the average score-- that's the row where z = 0. Then look at the broad middle range between z = -1 and z = 1. About 68% of people score between z = -1 and z = 1.

Intelligence Tests use Standard Scores abbreviated as SS. These scores take the place of the old IQ score. An average IQ is 100 -- about 68% of people score between 85 and 115.

Here's a table from Appendix B of Applied Statistics: Concepts for Counselors

Each row contains the equivalent score on a different scoring system. For example, a z-score of 1 equals a T score of 60, and a standard score of 115. The score is at the 84^th percentile.

z	T	Standard	Percentile Rank
3	80	145	99.9
2.5	75	138	99.4
2	70	130	97.7
1.5	65	123	93.3
1	60	115	84.1
.5	55	108	69.2
0	50	100	50.0
-.5	45	93	30.8
-1	40	85	15.9
-1.5	35	78	6.7
-2	30	70	2.3
-2.5	25	63	0.6
-3	20	55	0.1

Table Notes

z-scores, M = 0, SD = 1

T-scores, M = 50, SD = 10

SS-Standard Scores, M = 100, SD = 15

PR- Percentile Rank

Find more practical concepts in Applied Statistics: Concepts for Counselors

An inexpensive reference book for students and counselors

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Learn more at the book's website counselorstatistics

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