The Measurement of Intelligence Part 8

On the other hand, the child with an I Q of 120 or above is almost never found below the grade for his chronological age, and occasionally he is one or two grades above. Wherever located, his work is always "superior"

or "very superior," and the evidence suggests strongly that it would probably remain so even if extra promotions were granted.

CORRELATION BETWEEN I Q AND THE TEACHERS' ESTIMATES OF THE CHILDREN'S INTELLIGENCE. By the Pearson formula the correlation found between the I Q's and the teachers' rankings on a scale of five was .48. This is about what others have found, and is both high enough and low enough to be significant. That it is moderately high in so far corroborates the tests. That it is not higher means that either the teachers or the tests have made a good many mistakes.

When the data were searched for evidence on this point, it was found, as we have shown in Chapter II, that the fault was plainly on the part of the teachers. The serious mistakes were nearly all made with children who were either over age or under age for their grade, mostly the former. In estimating children's intelligence, just as in grading their school success, the teachers often failed to take account of the age factor. For example, the child whose mental age was, say, two years below normal, and who was enrolled in a cla.s.s with children about two years younger than himself, was often graded "average" in intelligence.

The tendency of teachers is to estimate a child's intelligence according to the quality of his school work _in the grade where he happens to be located_. This results in overestimating the intelligence of older, r.e.t.a.r.ded children, and underestimating the intelligence of the younger, advanced children. The disagreements between the tests and the teachers'

estimates are thus found, when a.n.a.lyzed, to confirm the validity of the test method rather than to bring it under suspicion.

THE VALIDITY OF THE INDIVIDUAL TESTS. The validity of each test was checked up by measuring it against the scale as a whole in the manner described on p. 55. For example, if 10-year-old children having 11-year intelligence succeed with a given test decidedly better than 10-year-old children who have 9-year intelligence, then either this test must be accepted as valid or the scale as a whole must be rejected. Since we know, however, that the scale as a whole has at least a reasonably high degree of reliability, this method becomes a sure and ready means of judging the worth of a test.

When the tests were tried out in this way it was found that some of those which have been most criticized have in reality a high correlation with intelligence. Among these are naming the days of the week, giving the value of stamps, counting thirteen pennies, giving differences between president and king, finding rhymes, giving age, distinguishing right and left, and interpretation of pictures. Others having a high reliability are the vocabulary tests, arithmetical reasoning, giving differences, copying a diamond, giving date, repeating digits in reverse order, interpretation of fables, the dissected sentence test, naming sixty words, finding omissions in pictures, and recognizing absurdities.

Among the somewhat less satisfactory tests are the following: repeating digits (direct order), naming coins, distinguishing forenoon and afternoon, defining in terms of use, drawing designs from memory, and aesthetic comparison. Binet's "line suggestion" test correlated so little with intelligence that it had to be thrown out. The same was also true of two of the new tests which we had added to the series for try-out.

Tests showing a medium correlation with the scale as a whole include arranging weights, executing three commissions, naming colors, giving number of fingers, describing pictures, naming the months, making change, giving superior definitions, finding similarities, reading for memories, reversing hands of clock, defining abstract words, problems of fact, bow-knot, induction test, and comprehension questions.

A test which makes a good showing on this criterion of agreement with the scale as a whole becomes immune to theoretical criticisms. Whatever it appears to be from mere inspection, it is a real measure of intelligence. Henceforth it stands or falls with the scale as a whole.

The reader will understand, of course, that no single test used alone will determine accurately the general level of intelligence. A great many tests are required; and for two reasons: (1) because intelligence has many aspects; and (2) in order to overcome the accidental influences of training or environment. If many tests are used no one of them need show more than a moderately high correlation with the scale as a whole.

As stated by Binet, "Let the tests be rough, if there are only enough of them."

CHAPTER VI

THE SIGNIFICANCE OF VARIOUS INTELLIGENCE QUOTIENTS

FREQUENCY OF DIFFERENT DEGREES OF INTELLIGENCE. Before we can interpret the results of an examination it is necessary to know how frequently an I Q of the size found occurs among unselected children. Our tests of 1000 unselected children enable us to answer this question with some degree of definiteness. A study of these 1000 I Q's shows the following significant facts:--

The lowest 1 % go to 70 or below, the highest 1 % reach 130 or above " " 2 % " " 73 " " " " 2 % " 128 " "

" " 3 % " " 76 " " " " 3 % " 125 " "

" " 5 % " " 78 " " " " 5 % " 122 " "

" " 10 % " " 85 " " " " 10 % " 116 " "

" " 15 % " " 88 " " " " 15 % " 113 " "

" " 20 % " " 91 " " " " 20 % " 110 " "

" " 25 % " " 92 " " " " 25 % " 108 " "

" " 33+1/3% " " 95 " " " " 33+1/3% " 106 " "

Or, to put some of the above facts in another form:--

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 " " "

CLa.s.sIFICATION 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 h.o.m.ogeneous 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 cla.s.sification of intelligence quotients:--

_I Q_ _Cla.s.sification_

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 cla.s.sifiable as feeble-mindedness.

70- 80 Border-line deficiency, sometimes cla.s.sifiable 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 cla.s.sed as imbeciles, and those below 20 or 25 as idiots. According to this cla.s.sification 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 cla.s.sification 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 ill.u.s.trative cases will perhaps give a fairly definite idea of the significance of various grades of intelligence.[28]

[28] The clinical descriptions to be given are not complete and are designed merely to aid the examiner in understanding the significance of intelligence quotients found.

FEEBLE-MINDEDNESS (RARELY ABOVE 75 I Q.) There are innumerable grades of mental deficiency ranging from somewhat below average intelligence to profound idiocy. In the literal sense every individual below the average is more or less mentally weak or feeble. Only a relatively small proportion of these, however, are technically known as feeble-minded. It is therefore necessary to set forth the criterion as to what const.i.tutes feeble-mindedness in the commonly accepted sense of that word.

The definition in most general use is the one framed by the Royal College of Physicians and Surgeons of London, and adopted by the English Royal Commission on Mental Deficiency. It is substantially as follows:--

_A feeble-minded person is one who is incapable, because of mental defect existing from birth or from an early age, (a) of competing on equal terms with his normal fellows; or (b) of managing himself or his affairs with ordinary prudence._

Two things are to be noted in regard to this definition: In the first place, it is stated in terms of social and industrial efficiency. Such efficiency, however, depends not merely on the degree of intelligence, but also on emotional, moral, physical, and social traits as well. This explains why some individuals with I Q somewhat below 75 can hardly be cla.s.sed as feeble-minded in the ordinary sense of the term, while others with I Q a little above 75 could hardly be cla.s.sified in any other group.

In the second place, the criterion set up by the definition is not very definite because of the vague meaning of the expression "ordinary prudence." Even the expression "competing on equal terms" cannot be taken literally, else it would include also those who are merely dull.

It is the second part of the definition that more nearly expresses the popular criterion, for as long as an individual manages his affairs in such a way as to be self-supporting, and in such a way as to avoid becoming a nuisance or burden to his fellowmen, he escapes the inst.i.tutions for defectives and may pa.s.s for normal.

The most serious defect of the definition comes from the lax interpretation of the term "ordinary prudence," etc. The popular standard is so low that hundreds of thousands of high grade defectives escape identification as such. Moreover, there are many grades of severity in social and industrial compet.i.tion. For example, most of the members of such families as the Jukes, the Nams, the Hill Folk, and the Kallikaks are able to pa.s.s as normal in their own crude environment, but when compelled to compete with average American stock their deficiency becomes evident. It is therefore necessary to supplement the social criterion with a more strictly psychological one.

For this purpose there is nothing else as significant as the I Q. All who test below 70 I Q by the Stanford revision of the Binet-Simon scale should be considered feeble-minded, and it is an open question whether it would not be justifiable to consider 75 I Q as the lower limit of "normal" intelligence. Certainly a large proportion falling between 70 and 75 can hardly be cla.s.sed as other than feeble-minded, even according to the social criterion.

_Examples of feeble-minded school children_

_F. C. Boy, age 8-6; mental age 4-2; I Q approximately 50._ From a very superior home. Has had the best medical care and other attention. Attended a private kindergarten until rejected because he required so much of the teacher's time and appeared uneducable. Will probably develop to about the 6- or 7-year mental level. High grade imbecile. Has since been committed to a state inst.i.tution. Cases as low as F. C. very rarely get into the public schools.

_R. W. Boy, age 13-10; mental age 7-6; I Q approximately 55._ Home excellent. Is p.u.b.escent. Because of age and maturity has been promoted to the third grade, though he can hardly do the work of the second. Has attended school more than six years.

Will probably never develop much if any beyond 8 years, and will never be self-supporting. Low-grade moron.

[Ill.u.s.tration: FIG. 4. DIAMOND DRAWN BY R. W., AGE 13-10; MENTAL AGE 7-6]