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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 84th 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















Learn more at the book's website  counselorstatistics

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