The Measurement of Intelligence

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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 class 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,
retarded children, and underestimating the intelligence of the younger,
advanced children. The disagreements between the tests and the teachers'
estimates are thus found, when analyzed, 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 " " "

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]

[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 constitutes
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
classed as feeble-minded in the ordinary sense of the term, while others
with I Q a little above 75 could hardly be classified 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
institutions for defectives and may pass 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 competition. For example, most of the
members of such families as the Jukes, the Nams, the Hill Folk, and the
Kallikaks are able to pass 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 classed 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 institution. 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 pubescent. 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.

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

_M. S. Girl, age 7-6; mental age 4-6; I Q 60._ Father a
gardener, home conditions and medical attention fair. Has twice
attempted first grade, but without learning to read more than a
few words. In each case teacher requested parents to withdraw
her. "Takes" things. Is considered "foolish" by the other
children. Will probably never develop beyond a mental level of
8 years.

_R. M. Boy, age 15; mental age 9; I Q 60._ Decidedly superior
home environment and care. After attending school eight years is
in fifth grade, though he cannot do the work of the fourth
grade. Parents unable to teach him to respect property. Boys
torment him and make his life miserable. At middle-moron level
and has probably about reached the limit of his development. Has
since been committed to a state institution.

[Illustration: FIG. 5. WRITING FROM DICTATION. R. M., AGE 15;
MENTAL AGE 9]

_S. M. Girl, age 19-2; mental age 10; I Q approximately 65 (not
counting age beyond 16)._ From very superior family. Has
attended public and private schools twelve years and has been
promoted to seventh grade, where she cannot do the work. Appears
docile and childlike, but is subject to spells of disobedience
and stubbornness. Did not walk until 4 years old. Plays with
young children. Susceptible to attention from men and has to be
constantly guarded. Writing excellent, knows the number
combinations, but missed all the absurdities and has the
vocabulary of an average 10-year-old. The type from which
prostitutes often come.

_R. H. Boy, age 14; mental age 8-4; I Q 65._ Father Irish,
mother Spanish. Family comfortable and home care average. Has
attended school eight years and is unable to do fourth-grade
work satisfactorily. Health excellent and attendance regular.
Reads in fourth reader without expression and with little
comprehension of what is read. Fair skill in number
combinations. Writing and drawing very poor. Cannot use a ruler.
Has no conception of an inch.

R. H. is described as high-tempered, irritable, lacking in
physical activity, clumsy, and unsteady. Plays little. Just
"stands around." Indifferent to praise or blame, has little
sense of duty, plays underhand tricks. Is slow, absent-minded,
easily confused, in thought, never shows appreciation or
interest. So apathetic that he does not hear commands. Voice
droning. Speech poor in colloquial expressions.

Three years later, at age of 17, was in a special class
attempting sixth-grade work. Reported as doing "absolutely
nothing" in that grade. Still sullen, indifferent, and slow in
grasping directions, and lacking in play interests. "No
apperception of anything, but has mastered such mechanical
things as reading (calling the words) and the fundamentals in
arithmetic."

In school work, moral traits, and out-of-school behavior R. H.
shows himself to be a typical case of moron deficiency.

_I. M. Girl, age 14-2; mental age 9; I Q approximately 65._
Father a laborer. Does unsatisfactory work in fourth grade.
Plays with little girls. A menace to the morals of the school
because of her sex interests and lack of self-restraint. Rather
good-looking if one does not hunt for appearances of
intelligence. Mental reactions intolerably slow. Will develop
but little further and will always pass as feeble-minded in any
but the very lowest social environment.

[Illustration: FIG. 6. BALL AND FIELD TEST. I. M., AGE 14-2;
MENTAL AGE 9]

_G. V. Boy, age 10; mental age 6-4; I Q 65._ Father Spanish,
mother English. Family poor but fairly respectable. Brothers and
sisters all retarded. In high first grade. Work all very poor
except writing, drawing, and hand work, in all of which he
excels. Is quiet and inactive, lacks self-confidence, and plays
little. Mentally slow, inert, "thick," and inattentive. Health
fair.

Three years later G. V. was in the low third grade and still
doing extremely poor work in everything except manual training,
drawing, and writing. Is not likely ever to go beyond the fourth
or fifth grade however long he remains in school.

_V. J. Girl, age 11-6; mental age 8; I Q 70._ Has been tested
three times in the last five years, always with approximately
the same result in terms of I Q. Home fair to inferior. Has been
in a special class two years and in school altogether nearly six
years. Is barely able to do third-grade work. Her
feeble-mindedness is recognized by teachers and by other pupils.
Belongs at about middle-moron to high-moron level.

_A. W. Boy, age 9-4; mental age 7; I Q 75._ A year and a half
ago he tested at 6-2. From superior family, brothers of very
superior intelligence. In school three years and has made about
a grade and a half. Has higher I Q than V. J. described above,
but his deficiency is fully as evident. Is generally recognized
as mentally defective. Slyly abstracted one of the pennies used
in the test and slipped it into his pocket. Has caused much
trouble at school by puncturing bicycle tires. High-grade moron.

[Illustration: FIG. 7. DIAMOND DRAWN BY A. W.]

_A. C. Boy, age 12; mental age 8-5; I Q 70._ From Portuguese
family of ten children. Has a feeble-minded brother. Parents in
comfortable circumstances and respectable. A. C. has attended
school regularly since he was 6 years old. Trying unsuccessfully
to do the work of the fourth grade. Reads poorly in the third
reader. Hesitates, repeats, miscalls words, and never gets the
thought. Writes about like a first-grade pupil. Cannot solve
such simple problems as "How many marbles can you buy for ten
cents if one marble costs five cents?" even when he has marbles
and money in his hands. Described by teacher as "mentally slow
and inert, inattentive, easily distracted, memory poor, ideas
vague and often absurd, does not appreciate stories, slow at
comprehending commands." Is also described as "unruly,
boisterous, disobedient, stubborn, and lacking sense of
propriety. Tattles."

Three years later, at age of 15, was in a special class and was
little if any improved. He had, however, learned the mechanics
of reading and had mastered the number combinations.
Deficiencies described as "of wide range." Conduct, however, had
improved. Was "working hard to get on."

A. C. must be considered definitely feeble-minded.

_H. S. Boy, age 11; mental age 8-3; I Q approximately 75._ At
8 years tested at 6. Parents highly educated, father a scholar.
Brother and sister of very superior intelligence. Started to
school at 7, but was withdrawn because of lack of progress.
Started again at 8 and is now doing poor work in the second
grade. Weakly and nervous. Painfully aware of his inability to
learn. During the test keeps saying, "I tried anyway," "It's all
I can do if I try my best, ain't it?" etc. Regarded defective by
other children. Will probably never be able to do work beyond
the fourth or fifth grade and is not likely to develop above the
11-year level, if as high.

[Illustration: FIG. 8. DRAWING DESIGNS FROM MEMORY. H. S.,
AGE 11; MENTAL AGE 8-3]

_I. S. Boy, age 9-6; mental age 7; I Q 75._ German parentage.
Started to school at 6. Now in low second grade and unable to do
the work. Health good. Inattentive, mentally slow and inert,
easily distracted, speech is monotone. Equally poor in reading,
writing, and numbers. I. S. is described as quiet, sullen,
indifferent, lazy, and stubborn. Plays little.

Three years later had advanced from low second to low fourth
grade, but was as poor as ever in his school work. "Miscalls the
simplest words." Moral traits unsatisfactory. May reach sixth or
seventh grade if he remains in school long enough.

I. S. learned to walk at 2 years and to talk at 3.

The above are cases of such marked deficiency that there could be no
disagreement among competent judges in classifying them in the group of
"feeble-minded." All are definitely institutional cases. It is a matter
of record, however, that one of the cases, H. S., was diagnosed by a
physician (without test) as "backward but not a defective." and with the
added encouragement that "the backwardness will be outgrown." Of course
the reverse is the case; the deficiency is becoming more and more
apparent as the boy approaches the age where more is expected of him.

In at least three of the above cases (S. M., I. S., and I. M.) the
teachers had not identified the backwardness as feeble-mindedness. Not
far from 2 children out of 100, or 2 out of 1000, in the average public
school are as defective as some of those just described. Teachers get so
accustomed to seeing a few of them in every group of 200 or 300 pupils
that they are likely to regard them as merely dull,--"dreadfully dull,"
of course,--but not defective.

Children like these, for their own good and that of other pupils, should
be kept out of the regular classes. They will rarely be equal to the
work of the fifth grade, however long they attend school. They will
make a little progress in a well-managed special class, but with the
approach of adolescence, at latest, the State should take them into
custodial care for its own protection.

BORDER-LINE CASES (USUALLY BETWEEN 70 AND 80 I Q). The border-line cases
are those which fall near the boundary generally recognized as such and
the higher group usually classed as normal but dull. They are the
doubtful cases, the ones we are always trying (rarely with success) to
restore to normality.

It must be emphasized, however, that this doubtful group is not marked
off by definite I Q limits. Some children with I Q as high as 75 or even
80 will have to be classified as feeble-minded; some as low as 70 I Q
may be so well endowed in other mental traits that they may manage as
adults to get along fairly well in a simple environment. The ability to
compete with one's fellows in the social and industrial world does not
depend upon intelligence alone. Such factors as moral traits, industry,
environment to be encountered, personal appearance, and influential
relatives are also involved. Two children classified above as
feeble-minded had an I Q as high as 75. In these cases the emotional,
moral, or physical qualities were so defective as to render a normal
social life out of the question. This is occasionally true even with an
I Q as high as 80. Some of the border-line cases, with even less
intelligence, may be so well endowed in other mental traits that they
are capable of becoming dependable unskilled laborers, and of supporting
a family after a fashion.

_Examples of border-line deficiency_

_S. F. Girl, age 17; mental age 11-6; I Q approximately 72
(disregarding age above 16 years)._ Father intelligent; mother
probably high-grade defective. Lives in a good home with aunt,
who is a woman of good sense and skillful in her management of
the girl. S. F. has attended excellent schools for eleven years
and has recently been promoted to the seventh grade. The teacher
admits, however, that she cannot do the work of that grade, but
says, "I haven't the heart to let her fail in the sixth grade
for the third time." She studies very hard and says she wants to
become a teacher! At the time the test was made she was actually
studying her books from two to three hours daily at home. The
aunt, who is very intelligent, had never thought of this girl as
feeble-minded, and had suffered much concern and humiliation
because of her inability to teach her to conduct herself
properly toward men and not to appropriate other people's
property.

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