Yes it IS valid

You can blather on about "nature versus nurture" all you wish, but the hard and ugly fact remains that intelligence varies. It is distributed with brutal unevenness. Like it or not, most people simply aren't all that bright. The following schematic, therefore, is as good as any, as an heuristic device if nothing else. Think of all the people you've known, and chances are, they fall proportionately into the given categories. Fewer than 2% of the population has an IQ in excess of 130.

I.Q. Range Intelligence Classification



1-19 Profound Mental Retardation
20–34 Severe Mental Retardation
35–49 Moderate Mental Retardation
50–69 Mild Mental Retardation
70–79 Borderline Mental Retardation
80-114 Average Intelligence
115-129 Bright
130-144 Moderately Gifted
145-159 Highly Gifted
160-175 Exceptionally Gifted
<175 Profoundly Gifted

In case you're wondering, my IQ has consistently tested at somewhere between 136 and 140, making me moderately gifted. This rating makes a great deal of sense to me: I'm smart enough to see how dumb most everything is, but not smart enough to be a world-class scientist, captain of industry, great original thinker, etc. Put simply, I'm stuck at base camp.



Other formulations:

Terman's classification:

<140 Genius or near genius
120-140 Very superior intelligence
110-120 Superior intelligence
90-110 Normal or average intelligence
80-90 Dullness
70-80 Borderline deficiency
>70 Definite feeble-mindedness

(Terman wrote the Stanford-Binet test (1), which has a standard deviation of 16.)

Later, David Wechsler thought that it would be much more legitimate to base his classifications on the Probable Error (PE) so his classification was (6):

Classification IQ Limits %
Very Superior <128 2.2
Superior 120-127 6.7
Bright Normal 111-119 16.1
Average 91-110 50
Dull Normal 80-90 16.1
Borderline 66-79 6.7
Defective >65 2.2

IN THE GOOD OLD DAYS, when we weren't afraid to call a moron a moron, instead of using obfuscations like "minimally exceptional," mental deficiency used to be more finely classified, using the following technical terms:

IQ Range Classification
70-80 Borderline deficiency
50-69 Moron
20-49 Imbecile
below 20 Idiot

All mental deficiency is now generally called mental retardation, though it really should be broadened to include most of the 'tards you meet on the street every day. The following is the current, politically correct classification of retardation in the United States:

IQ Range Classification
50-69 Mild
35-49 Moderate
20-34 Severe
below 20 Profound

Moreover, "educable mentally retarded" is roughly equivalent to mild mental retardation, and "trainable" mentally retarded is roughly equivalent to moderate.