| The child reaching | 110 | is equaled or excelled by | 20 | out of 100 |
| " "" (about) | 115 | " " " " " | 10 | """ |
| " " " " | 125 | " " " " " | 3 | """ |
| " " " " | 130 | " " " " " | 1 | """ |
Conversely, we may say regarding the subnormals that:—
| The child testing at (about) | 90 | is equaled or excelled by | 80 | out of 100 |
| " " " " " | 85 | " " " " " | 90 | """ |
| " " " " " | 75 | " " " " " | 97 | """ |
| " " " " " | 70 | " " " " " | 99 | """ |
Classification of intelligence quotients.
What do the above I Q’s imply in such terms as feeble-mindedness, border-line intelligence, dullness, normality, superior intelligence genius, etc.? When we use these terms two facts must be borne in mind: (1) That the boundary lines between such groups are absolutely arbitrary, a matter of definition only; and (2) that the individuals comprising one of the groups do not make up a homogeneous type.
Nevertheless, since terms like the above are convenient and will probably continue to be used, it is desirable to give them as much definiteness as possible. On the basis of the tests we have made, including many cases of all grades of intelligence, the following suggestions are offered for the classification of intelligence quotients:—
| I Q | Classification |
|---|---|
| Above 140 | “Near” genius or genius. |
| 120–140 | Very superior intelligence. |
| 110–120 | Superior intelligence. |
| 90–110 | Normal, or average, intelligence. |
| 80– 90 | Dullness, rarely classifiable as feeble-mindedness. |
| 70– 80 | Border-line deficiency, sometimes classifiable as dullness, often as feeble-mindedness. |
| Below 70 | Definite feeble-mindedness. |
Of the feeble-minded, those between 50 and 70 I Q include most of the morons (high, middle, and low), those between 20 or 25 and 50 are ordinarily to be classed as imbeciles, and those below 20 or 25 as idiots. According to this classification the adult idiot would range up to about 3-year intelligence as the limit, the adult imbecile would have a mental level between 3 and 7 years, and the adult moron would range from about 7-year to 11-year intelligence.
It should be added, however, that the classification of I Q’s for the various sub-grades of feeble-mindedness is not very secure, for the reason that the exact curves of mental growth have not been worked out for such grades. As far as the public schools are concerned this does not greatly matter, as they never enroll idiots and very rarely even the high-grade imbecile. School defectives are practically all of the moron and border-line grades, and these it is important teachers should be able to recognize. The following discussions and illustrative cases will perhaps give a fairly definite idea of the significance of various grades of intelligence.[28]