British Ability Scales 3: Score Classifications & Descriptions
Descriptive Classifications for IQ and Other Composite Cognitive Scores
Score classifications that are used in various individually-administered tests have changed
over time. Older classification systems tended to be value-laden, using such terms as
“Mentally Deficient,” and “Superior.” The Wechsler/Binet systems, which became widely
used, can be traced to the early 1900s. Pintner (1923, p. 77) and the Stanford-Binet (Terman
& Merrill, 1937; Merrill, 1938) had the following classification scheme:
Pintner
Classification
Feebleminded
Borderline
Backward
Normal
Bright
Very Bright
Very Superior
Stanford-Binet
Classification
Mentally Defective
Borderline Defective
Low Average
Normal or Average
High Average
Superior
Very Superior
Intelligence Quotient
0-69
70-79
80-89
90-109
110-119
120-129
130 and above
Interestingly, although the descriptive terms have changed over time, every subsequentlypublished major cognitive test battery has used the same score boundaries!
Classification labels are not in themselves objective statements, but are descriptors of an
individual’s level of general cognitive abilities recommended by an author as useful in
communicating with lay people.
The Wechsler scales used some of the same descriptors as those of Pintner and Merrill, but
these also changed over the years. For example, the WISC-R (1974) and WISC-IV (2003)
categories are as follows:
WISC-R
Classification
Mentally Deficient
Borderline
Below Average (Dull)
Average
Above Average (Bright)
Superior
Very Superior
WISC-IV
Classification
Extremely Low0-69
Borderline
Low Average
Average
High Average
Superior
Very Superior
Intelligence Quotient
70-79
80-89
90-109
110-119
120-129
130 and above
The BAS3 Descriptive Classifications
In recent years, there has been a tendency among authors and publishers to move to a
classification system that is less qualitative or evaluative, and more quantitative in its
descriptions. It is also desirable to have parallel descriptors above and below the mean. Thus
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the British Ability Scales, ever since their first publication in 1979, and the Differential Ability
Scales (1990, 2006) have used the following classification system:
BAS3
Classification
Very Low
Low
Below Average
Average
Above Average
High
Very High
GCA or
other composite score
69 and below
70-79
80-89
90-109
110-119
120-129
130 and above
Percentiles
1-2
3-8
9-24
25-74
75-90
91-97
98-99
How Should Descriptors be Used?
In the BAS3 SRS software, the GCA and SNC composites, and the cluster scores are reported
with confidence limits. The author recommends that if a score has confidence limits that are
in two categories, both categories should be used in describing the child’s score. For
example, if a child’s GCA score is 91, with 90% confidence limits of 86-97, it would be most
appropriate to report the child’s score as being in the average to below average range.
A Note on Percentile Ranges
The percentiles covered by the various standard scores are also shown in the table above.
From this it will be seen that the central category (Average) has a very neat and interesting
feature: the “Average” classification covers 50% of the population—it comprises all those
individuals whose scores are in the range of 90 to 109, who lie between the 25 th and 74th
percentiles. Thus according to these classification boundaries (which have been, and
continue to be, adopted by all major cognitive test authors and publishers) an average score
is defined as one that would be obtained by someone lying in the mid-fifty-percent of the
population.
A Final Note on the Definition of ‘Average’
Some educational psychology training courses teach that a region plus or minus one
standard deviation from the mean should be categorised as ‘average’ (i.e. the middle 68%).
It is important to bear in mind that this is merely a convention and that ‘average’ has only
one real statistical meaning – a score at the mean itself. Even then, statisticians prefer to
use ‘mean’ in order not to confuse it with the median or the mode.
There have been many different conventions used in psychometrics regarding the definition
of ‘average’. For example, British Army and Navy recruitment policies used to use the
middle 40% as their ‘average’ selection grade, a scale adopted by Alice Heim in her wellknown AH series. If stanines 4 to 6 are used as ‘average’ this is the middle 54%. Increasingly,
schools are using a three-point grading which splits performance into the bottom 25%, the
middle 50% and the top 25%. While 68% may have a convenient statistical meaning, this
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does not make it an ideal convention to convey accurate meaning to non-statisticians – the
middle 50% makes far more sense.
Whichever convention is used, it is critical that the meaning which the educational
psychologist is attaching to ‘average’ is conveyed to anyone being presented with the
results, or they may assume it to mean something else.
References
Elliott, C.D. (1990). Differential Ability Scales (DAS). San Antonio, TX: The Psychological
Corporation.
Elliott, C.D. (2006). Differential Ability Scales, 2nd edition (DAS-II). San Antonio, TX: Harcourt
Assessment.
Merrill, M.A. (1938). The significance of IQs on the Revised Stanford-Binet Scales. Journal of
Educational Psychology, 29, 641-651.
Pintner, R. (1923). Intelligence testing. New York: Holt, Rinehart & Winston.
Terman, L.M. & Merrill, M.A. (1937). Measuring intelligence. London: Harrap.
Wechsler, D. (1974). Manual for the Wechsler Intelligence Scale for Children-Revised (WISCR). New York: The Psychological Corporation.
Wechsler, D. (2003). Manual for the Wechsler Intelligence Scale for Children, 4th Edition
(WISC-IV). San Antonio, TX: Harcourt Assessment.
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