The Measurement of Intelligence

L >> Lewis Madison Terman >> The Measurement of Intelligence

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That the industrially inefficient are often of subnormal intelligence
has already been demonstrated in a number of psychological
investigations. Of 150 "hoboes" tested under the direction of the writer
by Mr. Knollin, at least 15 per cent belonged to the moron grade of
mental deficiency, and almost as many more were border-line cases. To be
sure, a large proportion were found perfectly normal, and a few even
decidedly superior in mental ability, but the ratio of mental deficiency
was ten or fifteen times as high as that holding for the general
population. Several had as low as 9- or 10-year intelligence, and one
had a mental level of 7 years. The industrial history of such subjects,
as given by themselves, was always about what the mental level would
lead us to expect--unskilled work, lack of interest in accomplishment,
frequent discharge from jobs, discouragement, and finally the "road."

The above findings have been fully paralleled by Mr. Glenn Johnson and
Professor Eleanor Rowland, of Reed College, who tested 108 unemployed
charity cases in Portland, Oregon. Both of these investigators made use
of the Stanford revision of the Binet scale, which is especially
serviceable in distinguishing the upper-grade defectives from normals.

It hardly needs to be emphasized that when charity organizations help
the feeble-minded to float along in the social and industrial world, and
to produce and rear children after their kind, a doubtful service is
rendered. A little psychological research would aid the united charities
of any city to direct their expenditures into more profitable channels
than would otherwise be possible.

OTHER USES OF INTELLIGENCE TESTS. Another important use of intelligence
tests is in the study of the factors which influence mental development.
It is desirable that we should be able to guard the child against
influences which affect mental development unfavorably; but as long as
these influences have not been sifted, weighed, and measured, we have
nothing but conjecture on which to base our efforts in this direction.

When we search the literature of child hygiene for reliable evidence as
to the injurious effects upon mental ability of malnutrition, decayed
teeth, obstructed breathing, reduced sleep, bad ventilation,
insufficient exercise, etc., we are met by endless assertion painfully
unsupported by demonstrated fact. We have, indeed, very little exact
knowledge regarding the mental effects of any of the factors just
mentioned. When standardized mental tests have come into more general
use, such influences will be easy to detect wherever they are really
present.

Again, the most important question of heredity is that regarding the
inheritance of intelligence; but this is a problem which cannot be
attacked at all without some accurate means of identifying the thing
which is the object of study. Without the use of scales for measuring
intelligence we can give no better answer as to the essential difference
between a genius and a fool than is to be found in legend and fiction.

Applying this to school children, it means that without such tests we
cannot know to what extent a child's mental performances are determined
by environment and to what extent by heredity. Is the place of the
so-called lower classes in the social and industrial scale the result of
their inferior native endowment, or is their apparent inferiority merely
a result of their inferior home and school training? Is genius more
common among children of the educated classes than among the children of
the ignorant and poor? Are the inferior races really inferior, or are
they merely unfortunate in their lack of opportunity to learn?

Only intelligence tests can answer these questions and grade the raw
material with which education works. Without them we can never
distinguish the results of our educational efforts with a given child
from the influence of the child's original endowment. Such tests would
have told us, for example, whether the much-discussed "wonder children,"
such as the Sidis and Wiener boys and the Stoner girl, owe their
precocious intellectual prowess to superior training (as their parents
believe) or to superior native ability. The supposed effects upon mental
development of new methods of mind training, which are exploited so
confidently from time to time (e.g., the Montessori method and the
various systems of sensory and motor training for the feeble-minded),
will have to be checked up by the same kind of scientific measurement.

In all these fields intelligence tests are certain to play an
ever-increasing role. With the exception of moral character there
is nothing as significant for a child's future as his grade of
intelligence. Even health itself is likely to have less influence in
determining success in life. Although strength and swiftness have always
had great survival value among the lower animals, these characteristics
have long since lost their supremacy in man's struggle for existence.
For us the rule of brawn has been broken, and intelligence has become
the decisive factor in success. Schools, railroads, factories, and the
largest commercial concerns may be successfully managed by persons who
are physically weak or even sickly. One who has intelligence constantly
measures opportunities against his own strength or weakness and adjusts
himself to conditions by following those leads which promise most toward
the realization of his individual possibilities.

All classes of intellects, the weakest as well as the strongest, will
profit by the application of their talents to tasks which are consonant
with their ability. When we have learned the lessons which intelligence
tests have to teach, we shall no longer blame mentally defective workmen
for their industrial inefficiency, punish weak-minded children because
of their inability to learn, or imprison and hang mentally defective
criminals because they lacked the intelligence to appreciate the
ordinary codes of social conduct.

CHAPTER II

SOURCES OF ERROR IN JUDGING INTELLIGENCE

ARE INTELLIGENCE TESTS SUPERFLUOUS? Binet tells us that he often
encountered the criticism that intelligence tests are superfluous, and
that in going to so much trouble to devise his measuring scale he was
forcing an open door. Those who made this criticism believed that the
observant teacher or parent is able to make an offhand estimate of a
child's intelligence which is accurate enough. "It is a stupid teacher,"
said one, "who needs a psychologist to tell her which pupils are not
intelligent." Every one who uses intelligence tests meets this attitude
from time to time.

This should not be surprising or discouraging. It is only natural that
those who are unfamiliar with the methods of psychology should
occasionally question their validity or worth, just as there are many
excellent people who do not "believe in" vaccination against typhoid and
small pox, operations for appendicitis, etc.

There is an additional reason why the applications of psychology have to
overcome a good deal of conservatism and skepticism; namely, the fact
that every one, whether psychologically trained or not, acquires in the
ordinary experiences of life a certain degree of expertness in the
observation and interpretation of mental traits. The possession of this
little fund of practical working knowledge makes most people slow to
admit any one's claim to greater expertness. When the astronomer tells
us the distance to Jupiter, we accept his statement, because we
recognize that our ordinary experience affords no basis for judgment
about such matters. But every one acquires more or less facility in
distinguishing the coarser differences among people in intelligence,
and this half-knowledge naturally generates a certain amount of
resistance to the more refined method of tests.

It should be evident, however, that we need more than the ability merely
to distinguish a genius from a simpleton, just as a physician needs
something more than the ability to distinguish an athlete from a man
dying of consumption. It is necessary to have a definite and accurate
diagnosis, one which will differentiate more finely the many degrees and
qualities of intelligence. Just as in the case of physical illness, we
need to know not merely that the patient is sick, but also why he is
sick, what organs are involved, what course the illness will run, and
what physical work the patient can safely undertake, so in the case of a
retarded child, we need to know the exact degree of intellectual
deficiency, what mental functions are chiefly concerned in the defect,
whether the deficiency is due to innate endowment, to physical illness,
or to faults of education, and what lines of mental activity the child
will be able to pursue with reasonable hope of success. In the diagnosis
of a case of malnutrition, the up-to-date physician does not depend upon
general symptoms, but instead makes a blood test to determine the exact
number of red corpuscles per cubic millimeter of blood and the exact
percentage of haemoglobin. He has learned that external appearances are
often misleading. Similarly, every psychologist who is experienced in
the mental examination of school children knows that his own or the
teacher's estimate of a child's intelligence is subject to grave and
frequent error.

THE NECESSITY OF STANDARDS. In the first place, in order to judge an
individual's intelligence it is necessary to have in mind some standard
as to what constitutes normal intelligence. This the ordinary parent or
teacher does not have. In the case of school children, for example, each
pupil is judged with reference to the average intelligence of the
class. But the teacher has no means of knowing whether the average for
her class is above, equal to, or below that for children in general. Her
standard may be too high, too low, vague, mechanical, or fragmentary.
The same, of course, holds in the case of parents or any one else
attempting to estimate intelligence on the basis of common observation.

THE INTELLIGENCE OF RETARDED CHILDREN USUALLY OVERESTIMATED. One of the
most common errors made by the teacher is to overestimate the
intelligence of the over-age pupil. This is because she fails to take
account of age differences and estimates intelligence on the basis of
the child's school performance in the grade where he happens to be
located. She tends to overlook the fact that quality of school work is
no index of intelligence unless age is taken into account. The question
should be, not, "Is this child doing his school work well?" but rather,
"In what school grade should a child of this age be able to do
satisfactory work?" A high-grade imbecile may do average work in the
first grade, and a high-grade moron average work in the third or fourth
grade, provided only they are sufficiently over-age for the grade in
question.

Our experience in testing children for segregation in special classes
has time and again brought this fallacy of teachers to our attention. We
have often found one or more feeble-minded children in a class after
the teacher had confidently asserted that there was not a single
exceptionally dull child present. In every case where there has been
opportunity to follow the later school progress of such a child the
validity of the intelligence test has been fully confirmed.

The following are typical examples of the neglect of teachers to take
the age factor into account when estimating the intelligence of the
over-age child:--

_A. R. Girl, age 11; in low second grade._ She was able to do
the work of this grade, not well, but passably. The teacher's
judgment as to this child's intelligence was "dull but not
defective." What the teacher overlooked was the fact that she
had judged the child by a 7-year standard, and that, instead of
only being able to do the work of the second grade
indifferently, a child of this age should have been equal to the
work of the fifth grade. In reality, A. R. is definitely
feeble-minded. Although she is from a home of average culture,
is 11 years old, and has attended school five years, she has
barely the intelligence of the average child of six years.

_D. C. Boy, age 17; in fifth grade._ His teacher knew that he
was dull, but had not thought of him as belonging to the class
of feeble-minded. She had judged this boy by the 11-year
standard and had perhaps been further misled by his normal
appearance and exceptionally satisfactory behavior. The Binet
test quickly showed that he had a mental level of approximately
9 years. There is little probability that his comprehension will
ever surpass that of the average 10-year-old.

_R. A. Boy, age 17; mental age 11; sixth grade; school work
"nearly average"; teacher's estimate of intelligence "average."_
Test plainly shows this child to be a high-grade moron, or
border-liner at best. Had attended school regularly 11 years and
had made 6 grades. Teacher had compared child with his
12-year-old classmates.

_H. A. Boy, age 14; mental age 9-6; low fourth grade; school
work "inferior"; teacher's estimate of intelligence "average."_
The teacher blamed the inferior quality of school work to "bad
home environment." As a matter of fact, the boy's father is
feeble-minded and the normality of the mother is questionable.
An older brother is in a reform school. We are perfectly safe in
predicting that this boy will not complete the eighth grade even
if he attends school till he is 21 years of age.

_F. I. Boy, age 12-11; mental age 9-4; third grade; school work
"average"; teacher's estimate of intelligence "average"; social
environment "average"; health good and attendance regular._
Intelligence and school success are what we should expect of an
average 9-year-old.

_D. A. Boy, age 12; mental age 9-2; third grade; school work
"inferior"; teacher's estimate of intelligence "average."_
Teacher imputes inferior school work to "absence from school and
lack of interest in books"; we have yet to find a child with a
mental age 25 per cent below chronological age who _was_
particularly interested in books or enthusiastic about school.

_C. U. Girl, age 10; mental age 7-8; second grade; school work
"average"; teacher's estimate of intelligence "average."_
Teacher blames adenoids and bad teeth for retardation. No doubt
of child's mental deficiency.

_P. I. Girl, age 8-10; mental age 6-7; has been in first grade
21/2 years; school work "average"; teacher's estimate of
intelligence "average."_ The mother and one brother of this girl
are both feeble-minded.

_H. O. Girl, age 7-10; mental age 5-2; first grade for 2 years;
school work "inferior"; teacher's estimate of intelligence
"average."_ The teacher nevertheless adds, "This child is not
normal, but her ability to respond to drill shows that she has
intelligence." It is of course true that even feeble-minded
children of 5-year intelligence are able to profit a little from
drill. Their weakness comes to light in their inability to
perform higher types of mental activity.

THE INTELLIGENCE OF SUPERIOR CHILDREN USUALLY UNDERESTIMATED. We have
already mentioned the frequent failure of teachers and parents to
recognize superior ability.[7] The fallacy here is again largely due to
the neglect of the age factor, but the resulting error is in the
opposite direction from that set forth above. The superior child is
likely to be a year or two younger than the average child of his grade,
and is accordingly judged by a standard which is too high. The following
are illustrations:--

[7] See p. 13 _ff._

_M. L. Girl, age 11-2; mental age "average adult" (16); sixth
grade; school work "superior"; teacher's estimate of
intelligence "average."_ Teacher credits superior school work to
"unusual home advantages." Father a college professor. The
teacher considers the child accelerated in school. In reality
she ought to be in the second year of high school instead of in
the sixth grade.

_H. A. Boy, age 11; mental age 14; sixth grade; school work
"average"; teacher's estimate of intelligence "average."_
According to the supplementary information the boy is
"wonderfully attentive," "studious," and possessed of
"all-round ability." The estimate of "average intelligence" was
probably the result of comparing him with classmates who
averaged about a year older.

_K. R. Girl, age 6-1; mental age 8-5; second grade; school work
"average"; teacher's estimate of intelligence "superior"; social
environment "average."_ Is it not evident that a child from
ordinary social environment, who does work of average quality in
the second grade when barely 6 years of age, should be judged
"very superior" rather than merely "superior" in intelligence?
The intelligence quotient of this girl is 140, which is not
reached by more than one child in two hundred.

_S. A. Boy, age 8-10; mental age 10-9; fourth grade; school work
"average"; teacher's estimate of intelligence "average."_
Teacher attributed school acceleration to "studiousness" and
"delight in school work." It would be more reasonable to infer
that these traits are indications of unusually superior
intelligence.

OTHER FALLACIES IN THE ESTIMATION OF INTELLIGENCE. Another source
of error in the teacher's judgment comes from the difficulty in
distinguishing genuine dullness from the mental condition which results
sometimes from unfavorable social environment or lack of training.

_V. P. Boy, age 7._ Had attended school one year and had
profited very little from the instruction. He had learned to
read very little, spoke chiefly in monosyllables, and seemed
"queer." The teacher suspected his intelligence and asked for a
mental examination. The Binet test showed that except for
vocabulary, which was unusually low, there was practically no
mental retardation. Inquiry disclosed the fact that the boy's
parents were uneducated deaf-mutes, and that the boy had
associated little with other children. Four years later this boy
was doing fairly well in school, though a year retarded because
of his unfavorable home environment.

_X. Y. Boy, age 10._ Son of a successful business man, he was
barely able to read in the second reader. The Binet test
revealed an intelligence level which was absolutely normal. The
boy was removed to a special class where he could receive
individual attention, and two years later was found doing good
work in a regular class of the fifth grade. His bad beginning
seemed to have been due to an unfavorable attitude toward school
work, due in turn to lack of discipline in the home, and to the
fact that because of the father's frequent change of business
headquarters the boy had never attended one school longer than
three months.

Another source of error in judging intelligence from common observation
is the tendency to overestimate the intelligence of the sprightly,
talkative, sanguine child, and to underestimate the intelligence of the
child who is less emotional, reacts slowly, and talks little. One
occasionally finds a feeble-minded adult, perhaps of only 9- or 10-year
intelligence, whose verbal fluency, mental liveliness, and
self-confidence would mislead the offhand judgment of even the
psychologist. One individual of this type, a border-line case at best,
was accustomed to harangue street audiences and had served as "major" in
"Kelly's Army," a horde of several hundred unemployed men who a few
years ago organized and started to march from San Francisco to
Washington.

BINET'S QUESTIONNAIRE ON TEACHERS' METHODS OF JUDGING INTELLIGENCE.[8]
Aroused by the skepticism so often shown toward his test method, Binet
decided to make a little study of the methods by which teachers are
accustomed to arrive at a judgment as to a child's intelligence.
Accordingly, through the cooeperation of the director of elementary
education in Paris, he secured answers from a number of teachers to the
following questions:--

[8] See p. 169 _ff._ of reference 2, at end of this book

1. _By what means do you judge the intelligence of your pupils?_
2. _How often have you been deceived in your judgments?_

About 40 replies were received. Most of the answers to the first
question were vague, one-sided, "verbal," or bookish. Only a few showed
much psychological discrimination as to what intelligence is and
what its symptoms are. There was a very general tendency to judge
intelligence by success in one or more of the school studies. Some
thought that ability to master arithmetic was a sure criterion. Others
were influenced almost entirely by the pupil's ability to read. One
teacher said that the child who can "read so expressively as to make you
feel the punctuation" is certainly intelligent, an observation which is
rather good, as far as it goes. A few judged intelligence by the pupil's
knowledge of such subjects as history and geography, which, as Binet
points out, is to confound intelligence with the ability to memorize.
"Memory," says Binet, is a "great simulator of intelligence." It is a
wise teacher who is not deceived by it. Only a small minority mentioned
resourcefulness in play, capacity to adjust to practical situations, or
any other out-of-school criteria.

Some suggested asking the pupil such questions as the following:--

"Why do you love your parents?" "If it takes three persons seven
hours to do a piece of work, would it take seven persons any
longer?" "Which would you rather have, a fourth of a pie, or a
half of a half?" "Which is heavier, a pound of feathers or a
pound of lead?" "If you had twenty cents what would you do with
it?"

A great many based their judgment mainly on the general appearance of
the face and eyes. An "active" or "passive" expression of the eyes was
looked upon as especially significant. One teacher thought that a mere
"glance of the eye" was sufficient to display the grade of intelligence.
If the eyes are penetrating, reflective, or show curiosity, the child
must be intelligent; if they are heavy and expressionless, he must be
dull. The mobility of countenance came in for frequent mention, also the
shape of the head.

No one will deny that intelligence displays itself to a greater or
less extent in the features; but how, asks Binet, are we going to
_standardize_ a "glance of the eye" or an "expression of curiosity" so
that it will serve as an exact measure of intelligence?

The fact is, the more one sees of feeble-minded children, the less
reliance one comes to place upon facial expression as a sign of
intelligence. Some children who are only slightly backward have the
general appearance of low-grade imbeciles. On the other hand, not a few
who are distinctly feeble-minded are pretty and attractive. With many
such children a ready smile takes the place of comprehension. If the
smile is rather sweet and sympathetic, as is often the case, the
observer is almost sure to be deceived.

As regards the shape of the head, peculiar conformation of the ears, and
other "stigmata," science long ago demonstrated that these are
ordinarily of little or no significance.

In reply to the second question, some teachers stated that they never
made a mistake, while others admitted failure in one case out of three.
Still others said, "Once in ten years," "once in twenty years," "once in
a thousand times," etc.

As Binet remarks, the answers to this question are not very enlightening.
In the first place, the teacher as a rule loses sight of the pupil when
he has passed from her care, and seldom has opportunity of finding out
whether his later success belies her judgment or confirms it. Errors go
undiscovered for the simple reason that there is no opportunity to check
them up. In the second place, her estimate is so rough that an error
must be very great in order to have any meaning. If I say that a man is
six feet and two inches tall, it is easy enough to apply a measuring
stick and prove the correctness or incorrectness of my assertion. But if
I say simply that the man is "rather tall," or "very tall," the error
must be very extreme before we can expose it, particularly since the
estimate can itself be checked up only by observation and not by
controlled experiment.

The teachers' answers seem to justify three conclusions:--

1. Teachers do not have a very definite idea of what constitutes
intelligence. They tend to confuse it variously with capacity for
memorizing, facility in reading, ability to master arithmetic, etc. On
the whole, their standard is too academic. They fail to appreciate the
one-sidedness of the school's demands upon intelligence.

In a quaintly humorous passage discussing this tendency, Binet
characterizes the child in a class as _denature_, a French word which we
may translate (though rather too literally) as "denatured." Too often
this "denatured" child of the classroom is the only child the teacher
knows.

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