The Measurement of Intelligence

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However, an examination of the scale will show that the choice of tests
was not guided entirely by any single formula as to the nature of
intelligence. Binet's approach was a many-sided one. The scale includes
tests of time orientation, of three or four kinds of memory, of
apperception, of language comprehension, of knowledge about common
objects, of free association, of number mastery, of constructive
imagination, and of ability to compare concepts, to see contradictions,
to combine fragments into a unitary whole, to comprehend abstract terms,
and to meet novel situations.

OTHER CONCEPTIONS OF INTELLIGENCE. It is interesting to compare Binet's
conception of intelligence with the definitions which have been offered
by other psychologists. According to Ebbinghaus, for example, the
essence of intelligence lies in comprehending together in a unitary,
meaningful whole, impressions and associations which are more or less
independent, heterogeneous, or even partly contradictory. "Intellectual
ability consists in the elaboration of a whole into its worth and
meaning by means of many-sided combination, correction, and completion
of numerous kindred associations.... It is a _combination activity_."

Meumann offers a twofold definition. From the psychological point of
view, intelligence is the power of independent and creative elaboration
of new products out of the material given by memory and the senses. From
the practical point of view, it involves the ability to avoid errors, to
surmount difficulties, and to adjust to environment.

Stern defines intelligence as "the general capacity of an individual
consciously to adjust his thinking to new requirements: it is general
adaptability to new problems and conditions of life."

Spearman, Hart, and others of the English school define intelligence as
a "common central factor" which participates in all sorts of
special mental activities. This factor is explained in terms of a
psycho-physiological hypothesis of "cortex energy," "cerebral
plasticity," etc.

The above definitions are only to a slight extent contradictory or
inharmonious. They differ mainly in point of view or in the location of
the emphasis. Each expresses a part of the truth, and none all of it. It
will be evident that the conception of Binet is broad enough to include
the most important elements in each of the other definitions quoted.

GUIDING PRINCIPLES IN CHOICE AND ARRANGEMENT OF TESTS. In choosing his
tests Binet was guided by the conception of intelligence which we have
set forth above. Tests were devised which would presumably bring
into play the various mental processes thought to be concerned in
intelligence, and then these tests were tried out on normal children of
different ages. If the percentage of passes for a given test increased
but little or not at all in going from younger to older children this
test was discarded. On the other hand, if the proportion of passes
increased rapidly with age, and if children of a given age, who on other
grounds were known to be bright, passed more frequently than children of
the same age who were known to be dull, then the test was judged a
satisfactory test of intelligence. As we have shown elsewhere,[13]
practically all of Binet's tests fulfill these requirements reasonably
well, a fact which bears eloquent testimony to the keen psychological
insight of their author.

[13] See p. 55.

In arranging the tests into a system Binet's guiding principle was to
find an arrangement of the tests which would cause an average child of
any given age to test "at age"; that is, the average 5-year-old must
show a mental age of 5 years, the average 8-year-old a mental age of
8 years, etc. In order to secure this result Binet found that his data
seemed to require the location of an individual test in that year where
it was passed by about two thirds to three fourths of unselected
children.

It was in the assembling of the tests that the most serious faults of
the scale had their origin. Further investigation has shown that a great
many of the tests were misplaced as much as one year, and several of
them two years. On the whole, the scale as Binet left it was decidedly
too easy in the lower ranges, and too difficult in the upper. As a
result, the average child of 5 years was caused to test at not far from
6 years, the average child of 12 years not far from 11. In the Stanford
revision an effort has been made to correct this fault, along with
certain other generally recognized imperfections.

SOME AVOWED LIMITATIONS OF THE BINET TESTS. The Binet tests have often
been criticized for their unfitness to perform certain services which in
reality they were never meant to render. This is unfair. We cannot make
a just evaluation of the scale without bearing in mind its avowed
limitations.

For example, the scale does not pretend to measure the entire mentality
of the subject, but only _general intelligence_. There is no pretense of
testing the emotions or the will beyond the extent to which these
naturally display themselves in the tests of intelligence. The scale was
not designed as a tool for the analysis of those emotional or volitional
aberrations which are concerned in such mental disorders as hysteria,
insanity, etc. These conditions do not present a progressive reduction
of intelligence to the infantile level, and in most of them other
factors besides intelligence play an important role. Moreover, even in
the normal individual the fruitfulness of intelligence, the direction in
which it shall be applied, and its methods of work are to a certain
extent determined by the extraneous factors of emotion and volition.

It should, nevertheless, be pointed out that defects of intelligence, in
a large majority of cases, also involve disturbances of the emotional
and volitional functions. We do not expect to find perfectly normal
emotions or will power of average strength coupled with marked
intellectual deficiency, and as a matter of fact such a combination is
rare indeed. In the course of an examination with the Binet tests, the
experienced clinical psychologist is able to gain considerable insight
into the subject's emotional and volitional equipment, even though the
method was designed primarily for another purpose.

A second misunderstanding can be avoided by remembering that the Binet
scale does not pretend to bring to light the idiosyncrasies of special
talent, but only to measure the general level of intelligence. It cannot
be used for the discovery of exceptional ability in drawing, painting,
music, mathematics, oratory, salesmanship, etc., because no effort is
made to explore the processes underlying these abilities. It can,
therefore, never serve as a _detailed chart_ for the vocational guidance
of children, telling us which will succeed in business, which in art,
which in medicine, etc. It is not a new kind of phrenology. At the same
time, as we have already pointed out, _it is capable of bounding roughly
the vocational territory in which an individual's intelligence will
probably permit success, nothing else preventing_.[14]

[14] See p. 17.

In the third place, it must not be supposed that the scale can be used
as a complete pedagogical guide. Although intelligence tests furnish
data of the greatest significance for pedagogical procedure, they do not
suggest the appropriate educational methods in detail. These will
have to be worked out in a practical way for the various grades of
intelligence, and at great cost of labor and patience.

Finally, in arriving at an estimate of a subject's grade of intelligence
and his susceptibility to training, it would be a mistake to ignore the
data obtainable from other sources. No competent psychologist, however
ardent a supporter of the Binet method he might be, would recommend such
a policy. Those who accept the method as all-sufficient are as much in
error as those who consider it as no more important than any one of a
dozen other approaches. Standardized tests have already become and will
remain by far the most reliable single method for grading intelligence,
but the results they furnish will always need to be interpreted in the
light of supplementary information regarding the subject's personal
history, including medical record, accidents, play habits, industrial
efficiency, social and moral traits, school success, home environment,
etc. Without question, however, the improved Binet tests will contribute
more than all other data combined to the end of enabling us to forecast
a child's possibilities of future improvement, and this is the
information which will aid most in the proper direction of his
education.

CHAPTER IV

NATURE OF THE STANFORD REVISION AND EXTENSION

Although the Binet scale quickly demonstrated its value as an instrument
for the classification of mentally-retarded and otherwise exceptional
children, it had, nevertheless, several imperfections which greatly
limited its usefulness. There was a dearth of tests at the higher mental
levels, the procedure was so inadequately defined that needless
disagreement came about in the interpretation of data, and so many of
the tests were misplaced as to make the results of an examination more
or less misleading, particularly in the case of very young subjects and
those near the adult level. It was for the purpose of correcting
these and certain other faults that the Stanford investigation was
planned.[15]

[15] The writer wishes to acknowledge his very great indebtedness to
Miss Grace Lyman, Dr. George Ordahl, Dr. Louise Ellison Ordahl, Miss
Neva Galbreath, Mr. Wilford Talbert, Dr. J. Harold Williams, Mr. Herbert
E. Knollin, and Miss Irene Cuneo for their cooeperation in making the
tests on which the Stanford revision is chiefly based. Without their
loyal assistance the investigation could not have been carried through.

Grateful acknowledgment is also made to the many public school teachers
and principals for their generous and invaluable cooeperation in
furnishing subjects for the tests, and in supplying, sometimes at
considerable cost of labor, the supplementary information which was
called for regarding the pupils tested. Their contribution was made in
the interest of educational science, and without expectation of personal
benefits of any kind. Their professional spirit cannot be too highly
commended.

SOURCES OF DATA. Our revision is the result of several years of work,
and involved the examination of approximately 2300 subjects, including
1700 normal children, 200 defective and superior children, and more than
400 adults.

Tests of 400 of the 1700 normal children had been made by Childs and
Terman in 1910-11, and of 300 children by Trost, Waddle, and Terman in
1911-12. For various reasons, however, the results of these tests did
not furnish satisfactory data for a thoroughgoing revision of the scale.
Accordingly a new investigation was undertaken, somewhat more extensive
than the others, and more carefully planned. Its main features may be
described as follows:--

1. The first step was to assemble as nearly as possible all the results
which had been secured for each test of the scale by all the workers of
all countries. The result was a large sheet of tabulated data for each
individual test, including percentages passing the test at various ages,
conditions under which the results were secured, method of procedure,
etc. After a comparative study of these data, and in the light of
results we had ourselves secured, a provisional arrangement of the tests
was prepared for try-out.

2. In addition to the tests of the original Binet scale, 40 additional
tests were included for try-out. This, it was expected, would make
possible the elimination of some of the least satisfactory tests, and at
the same time permit the addition of enough new ones to give at least
six tests, instead of five, for each age group.

3. A plan was then devised for securing subjects who should be as nearly
as possible representative of the several ages. The method was to select
a school in a community of average social status, a school attended by
all or practically all the children in the district where it was
located. In order to get clear pictures of age differences the tests
were confined to children who were within two months of a birthday. To
avoid accidental selection, _all_ the children within two months of a
birthday were tested, in whatever grade enrolled. Tests of foreign-born
children, however, were eliminated in the treatment of results. There
remained tests of approximately 1000 children, of whom 905 were between
5 and 14 years of age.

4. The children's responses were, for the most part, recorded
_verbatim_. This made it possible to re-score the records according
to any desired standard, and thus to fit a test more perfectly to the
age level assigned it.

5. Much attention was given to securing uniformity of procedure. A
half-year was devoted to training the examiners and another half-year to
the supervision of the testing. In the further interests of uniformity
all the records were scored by one person (the writer).

METHOD OF ARRIVING AT A REVISION. The revision of the scale below
the 14-year level was based almost entirely on the tests of the
above-mentioned 1,000 unselected children. The guiding principle was to
secure an arrangement of the tests and a standard of scoring which would
cause the median mental age of the unselected children of each age group
to coincide with the median chronological age. That is, a correct scale
must cause the _average_ child of 5 years to test exactly at 5, the
_average_ child at 6 to test exactly at 6, etc. Or, to express the same
fact in terms of intelligence quotient,[16] a correct scale must give a
median intelligence quotient of unity, or 100 per cent, for unselected
children of each age.

[16] The intelligence quotient (often designated as I Q) is the ratio of
mental age to chronological age. (See pp. 65 _ff._ and 78 _ff._)

If the median mental age resulting at any point from the provisional
arrangement of tests was too high or too low, it was only necessary to
change the location of certain of the tests, or to change the standard
of scoring, until an order of arrangement and a standard of passing were
found which would throw the median mental age where it belonged. We had
already become convinced, for reasons too involved for presentation
here, that no satisfactory revision of the Binet scale was possible on
any theoretical considerations as to the percentage of passes which an
individual test ought to show in a given year in order to be considered
standard for that year.

As was to be expected, the first draft of the revision did not prove
satisfactory. The scale was still too hard at some points, and too easy
at others. In fact, three successive revisions were necessary, involving
three separate scorings of the data and as many tabulations of the
mental ages, before the desired degree of accuracy was secured. As
finally revised, the scale gives a median intelligence quotient closely
approximating 100 for the unselected children of each age from 4 to 14.

Since our school children who were above 14 years and still in the
grades were retarded left-overs, it was necessary to base the revision
above this level on the tests of adults. These included 30 business men
and 150 "migrating" unemployed men tested by Mr. H. E. Knollin, 150
adolescent delinquents tested by Mr. J. Harold Williams, and 50
high-school students tested by the writer.

The extension of the scale in the upper range is such that ordinarily
intelligent adults, little educated, test up to what is called the
"average adult" level. Adults whose intelligence is known from other
sources to be superior are found to test well up toward the "superior
adult" level, and this holds whether the subjects in question are well
educated or practically unschooled. The almost entirely unschooled
business men, in fact, tested fully as well as high-school juniors and
seniors.

Figure 1 shows the distribution of mental ages for 62 adults, including
the 30 business men and the 32 high-school pupils who were over 16 years
of age. It will be noted that the middle section of the graph represents
the "mental ages" falling between 15 and 17. This is the range which we
have designated as the "average adult" level. Those above 17 are called
"superior adults," those between 13 and 15, "inferior adults." Subjects
much over 15 years of age who test in the neighborhood of 12 years may
ordinarily be considered border-line cases.

[Illustration: FIG. 1. DISTRIBUTION OF MENTAL AGES OF 62 NORMAL ADULTS]

The following method was employed for determining the validity of a
test. The children of each age level were divided into three groups
according to intelligence quotient, those testing below 90, those
between 90 and 109, and those with an intelligence quotient of 110 or
above. The percentages of passes on each individual test at or near that
age level were then ascertained separately for these three groups. If a
test fails to show a decidedly higher proportion of passes in the
superior I Q group than in the inferior I Q group, it cannot be regarded
as a satisfactory test of intelligence. On the other hand, a test which
satisfies this criterion must be accepted as valid or the entire scale
must be rejected. Henceforth it stands or falls with the scale as a
whole.

When tried out by this method, some of the tests which have been most
criticized showed a high degree of reliability; certain others which
have been considered excellent proved to be so little correlated with
intelligence that they had to be discarded.

After making a few necessary eliminations, 90 tests remained, or 36 more
than the number included in the Binet 1911 scale. There are 6 at each
age level from 3 to 10, 8 at 12, 6 at 14, 6 at "average adult," 6 at
"superior adult," and 16 alternative tests. The alternative tests, which
are distributed among the different groups, are intended to be used only
as substitutes when one or more of the regular tests have been rendered,
by coaching or otherwise, undesirable.[17]

[17] See p. 137 _ff._ for explanations regarding the calculation of
mental age and the use of alternative tests.

Of the 36 new tests, 27 were added and standardized in the various
Stanford investigations. Two tests were borrowed from the Healy-Fernald
series, one from Kuhlmann, one was adapted from Bonser, and the
remaining five were amplifications or adaptations of some of the earlier
Binet tests.

Following is a complete list of the tests of the Stanford revision.
Those designated _al._ are alternative tests. The guide for giving and
scoring the tests is presented at length in Part II of this volume.

_The Stanford revision and extension_

_Year III._ (_6 tests, 2 months each._)
1. Points to parts of body. (3 to 4.)
Nose; eyes; mouth; hair.
2. Names familiar objects. (3 to 5.)
Key, penny, closed knife, watch, pencil.
3. Pictures, enumeration or better. (At least 3 objects enumerated
in one picture.)
(a) Dutch Home; (b) River Scene; (c) Post-Office.
4. Gives sex.
5. Gives last name.
6. Repeats 6 to 7 syllables. (1 to 3.)
Al. Repeats 3 digits. (1 success in 3 trials. Order correct.)

_Year IV._ (_6 tests, 2 months each._)
1. Compares lines. (3 trials, no error.)
2. Discrimination of forms. (Kuhlmann.) (Not over 3 errors.)
3. Counts 4 pennies. (No error.)
4. Copies square. (Pencil. 1 to 3.)
5. Comprehension, 1st degree. (2 to 3.) (Stanford addition.)
"What must you do": "When you are sleepy?" "Cold?" "Hungry?"
6. Repeats 4 digits. (1 to 3. Order correct.) (Stanford addition.)
Al. Repeats 12 to 13 syllables. (1 to 3 absolutely correct, or 2 with
1 error each.)

_Year V._ (_6 tests, 2 months each._)
1. Comparison of weights. (2 to 3.)
3-15; 15-3; 3-15.
2. Colors. (No error.)
Red; yellow; blue; green.
3. AEsthetic comparison. (No error.)
4. Definitions, use or better. (4 to 6.)
Chair; horse; fork; doll; pencil; table.
5. Patience, or divided rectangle. (2 to 3 trials. 1 minute each.)
6. Three commissions. (No error. Order correct.)
Al. Age.

_Year VI._ (_6 tests, 2 months each._)
1. Right and left. (No error.)
Right hand; left ear; right eye.
2. Mutilated pictures. (3 to 4 correct.)
3. Counts 13 pennies. (1 to 2 trials, without error.)
4. Comprehension, 2d degree. (2 to 3.) "What's the thing for
you to do":
(a) "If it is raining when you start to school?"
(b) "If you find that your house is on fire?"
(c) "If you are going some place and miss your car?"
5. Coins. (3 to 4.)
Nickel; penny; quarter; dime.
6. Repeats 16 to 18 syllables. (1 to 3 absolutely correct, or 2
with 1 error each.)
Al. Morning or afternoon.

_Year VII._ (_6 tests, 2 months each._)
1. Fingers. (No error.) Right; left; both.
2. Pictures, description or better. (Over half of performance
description:) Dutch Home; River Scene; Post-Office.
3. Repeats 5 digits. (1 to 3. Order correct.)
4. Ties bow-knot. (Model shown. 1 minute.) (Stanford addition.)
5. Gives differences. (2 to 3.)
Fly and butterfly; stone and egg; wood and glass.
6. Copies diamond. (Pen. 2 to 3.)
Al. 1. Names days of week. (Order correct. 2 to 3 checks correct.)
Al. 2. Repeats 3 digits backwards. (1 to 3.)

_Year VIII._ (_6 tests, 2 months each._)
1. Ball and field. (Inferior plan or better.) (Stanford addition.)
2. Counts 20 to 1. (40 seconds. 1 error allowed.)
3. Comprehension, 3d degree. (2 to 3.) "What's the thing for you to
do":
(a) "When you have broken something which belongs to some one
else?"
(b) "When you are on your way to school and notice that you are
in danger of being tardy?"
(c) "If a playmate hits you without meaning to do it?"
4. Gives similarities, two things. (2 to 4.) (Stanford addition.)
Wood and coal; apple and peach; iron and silver; ship and
automobile.
5. Definitions superior to use. (2 to 4.)
Balloon; tiger; football; soldier.
6. Vocabulary, 20 words. (Stanford addition. For list of words used,
see record booklet.)
Al. 1. First six coins. (No error.)
Al. 2. Dictation. ("See the little boy." Easily legible. Pen. 1 minute.)

_Year IX._ (_6 tests, 2 months each._)
1. Date. (Allow error of 3 days in _c_, no error in _a_, _b_, or _d_.)
(a) day of week; (b) month; (c) day of month; (d) year.
2. Weights. (3, 6, 9, 12, 15. Procedure not illustrated. 2 to 3.)
3. Makes change. (2 to 3. No coins, paper, or pencil.)
10--4; 15--12; 25--4.
4. Repeats 4 digits backwards. (1 to 3.) (Stanford addition.)
5. Three words. (2 to 3. Oral. 1 sentence or not over 2 cooerdinate
clauses.)
Boy, river, ball; work, money, men; desert, rivers, lakes.
6. Rhymes. (3 rhymes for two of three words. 1 minute for each part.)
Day; mill; spring.
Al. 1. Months. (15 seconds and 1 error in naming. 2 checks of 3 correct.)
Al. 2. Stamps, gives total value. (Second trial if individual values are
known.)

_Year X._ (_6 tests, 2 months each._)
1. Vocabulary, 30 words. (Stanford addition.)
2. Absurdities. (4 to 5. Warn. Spontaneous correction allowed.) (Four
of Binet's, one Stanford.)
3. Designs. (1 correct, 1 half correct. Expose 10 seconds.)
4. Reading and report. (8 memories. 35 seconds and 2 mistakes in
reading.) (Binet's selection.)
5. Comprehension, 4th degree. (2 to 3. Question may be repeated.)
(a) "What ought you to say when some one asks your opinion
about a person you don't know very well?"
(b) "What ought you to do before undertaking (beginning)
something very important?"
(c) "Why should we judge a person more by his actions than by
his words?"
6. Names 60 words. (Illustrate with clouds, dog, chair, happy.)
Al. 1. Repeats 6 digits. (1 to 2. Order correct.) (Stanford addition.)
Al. 2. Repeats 20 to 22 syllables. (1 to 3 correct, or 2 with 1 error
each.)
Al. 3. Form board. (Healy-Fernald Puzzle A. 3 times in 5 minutes.)

_Year XII._ (_8 tests, 3 months each._)
1. Vocabulary, 40 words. (Stanford addition.)
2. Abstract words. (3 to 5.)
Pity; revenge; charity; envy; justice.
3. Ball and field. (Superior plan.) (Stanford addition.)
4. Dissected sentences. (2 to 3. 1 minute each.)
5. Fables. (Score 4; i.e., two correct or the equivalent in half
credits.) (Stanford addition.)
Hercules and Wagoner; Maid and Eggs; Fox and Crow;
Farmer and Stork; Miller, Son, and Donkey.
6. Repeats 5 digits backwards. (1 to 3.) (Stanford addition.)
7. Pictures, interpretation. (3 to 4. "Explain this picture.")
Dutch Home; River Scene; Post-Office; Colonial Home.
8. Gives similarities, three things. (3 to 5.) (Stanford addition.)
Snake, cow, sparrow; book, teacher, newspaper; wool, cotton,
leather; knife-blade, penny, piece of wire; rose, potato,
tree.

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