WHAT THESE TESTS MEASURE
The most natural question and one that is frequently asked is:
“What, precisely, do psychological tests measure?”
It is a question that is easier to ask than to answer.
It is simple enough to say that mental tests are designed to measure the
natural or inherent mental capacity of the individual, but in order to
approach a clear understanding of just what this means we must first
define what is meant by the term “mental capacity.”
As a matter of scientific fact, the term “mental capacity” can hardly be
regarded as accurate, although it is the best term we have to describe
the qualities which determine the individual’s ability to perform acts
requiring conscious thought. Psychological and biological science no
longer regard the human mind as something different from or in any way
apart from the human body. The idea that there is such an entity as a
mind that operates even in the slightest degree without reference to and
independent of the physical body must be dismissed, if we are to grasp
clearly the principles and methods of mental tests.
To the psychologist the mind is merely a specialized organ of the
physical body. The intangible something, which is what is usually meant
when persons speak of the human mind, is merely the sum of all the
sensations, feelings, and judgments resulting from the delicate
adjustment of an almost infinite number of nerve fibres which in
themselves are a part of the physical body. One may have at birth a
plentiful supply or a poor supply of potential nerve endings which are
ready to be organized and coördinated by experience and training, but
unless one has the opportunity to learn from study and experience, the
desirable connections may never be developed.
The maximum capacity of the mind in any particular field is, therefore,
practically determined by physical inheritance of an abundant supply of
nerve endings. Thus, it may be that one individual is born with two or
three times as many nerve terminals connecting at the point at the back
of the eyeball where the optic nerve—which is simply a bundle or rope of
nerve fibres—is attached to the mechanical apparatus upon which the
reflection of objects passing before the field of vision is registered.
Such an individual’s powers of observation are normally greater than
those of the person of less fortunate heredity in this respect, whose
lesser number of terminals of the optic nerve fibres limit his powers of
optical perception and observation. Thus, one person may see at a glance
a hundred details, all of which register sharply upon his consciousness,
while another sees only the gross outlines and shadows, and in between
is the average person who sees some details but not all.
It is well known to psychologists and biologists, although not generally
understood by those who have not made a special study of these sciences,
that mental _capacity_ does not change or increase materially after the
individual has reached maturity. It may be diminished through accident
or disease, but the chief increase in adult life is in the volume and
variety of stored-up impressions. The average girl of eighteen or boy of
twenty has reached the approximate limit of his or her mental capacity.
The mental tank will never grow much larger. It may be half empty or
almost entirely vacant, but unless at the average age of university
sophomores scientific mental tests prove the individual to be possessed
of average or better than average mental capacity, it is futile to
expect any great intellectual development to take place in later life.
But while the maximum capacity of the mind depends upon physical
inheritance, the actual ability which is necessarily reflected in the
scores made by a person subjected to mental tests is determined by the
number and variety of nerve connections that have actually been made by
environment or training. Inheritance sets the maximum limit, but as a
matter of practice this maximum is never reached, or at least is so
seldom reached by any individual that it can hardly be said of any human
being that he has developed his mind in any direction to the utmost
limit of its capacity. What we actually measure in scientific mental
tests is a complex of natural or inherent abilities plus the results of
education and training; because, while it is possible to a considerable
extent to eliminate by properly devised tests a record of the
individual’s acquired knowledge, it is practically impossible to
distinguish between acquired and inherent mental ability.
Note carefully the distinction between mental _ability_ and mental
_capacity_. Mental ability in any individual is always less than his
mental capacity. If, therefore, the mental ability as determined by
scientific tests reaches the highest point on the scale of measurement,
whatever that may be, it follows that the mental capacity of the
individual making a perfect score is even greater than the scale is
designed to measure, and how much greater can only be determined by
setting up new tests based upon higher standards.
The result of any scientific test simply indicates the wealth of nerve
connections that are ready to be made when the stimulus necessary to
their establishment is applied. It must be understood that no one having
a sound claim to the possession of scientific knowledge can contend that
there are tests in existence that actually measure with complete
precision the inherited as distinguished from the acquired mental
characteristics. It is not conceded, however, that such precise
measurements cannot be made if at any time it becomes necessary or
desirable to do so. For all practical present-day purposes it is
sufficient that psychological tests shall measure mental qualities which
are manifested by the individual’s ability to express them by action or
speech. The classification of individuals relative to one another and
with reference to the possession of a particular mental ability or group
of abilities is, therefore, necessarily based upon their relative
ability to express in some intelligible and unmistakable fashion their
mental power and qualities.
Back of this power of expression may lie hidden and undreamed-of
capacities of which the individual himself may be vaguely conscious but
of which he can give no outward manifestation. It may be, for example,
that an individual is gifted with unusual powers of perception through
the eyes, ears, and the senses of touch, smell, and taste but that he is
deficient in nerve fibres and connections controlling the voluntary
muscles by which human beings translate sensations into action and
speech. This is hardly likely, as a physiological fact, to occur; the
individual born with rich nerve endings in one part of the physical body
is more likely to have a proportionate supply of nerve endings in all
other parts of the body than to be deficient in one part and amply
supplied in another. As rare exceptions, however, there are individuals
who in infancy have, through accident or disease, lost certain groups of
nerve connections while retaining unusually rich groups in other parts
of the body. There is, of course, the most famous case in modern
history, that of Helen Keller, whose auditory and optical nerve
connections were lost through disease in early infancy, but whose
unusual inherent mental capacity has been able to demonstrate itself
through other and extraordinary means as a result of training and
education.
But in ordinary life, if a man or a woman has some mental quality which
does not express itself in an action which other persons can see or hear
and know about, then it is not socially important. It is of consequence
only to the individual and it is of little social service to undertake
to measure these obscure and unexpressed and inexpressible capacities,
as they can never, until they find means of expression, affect the
individual’s ability or efficiency in any occupation. It is not that
these things cannot be measured. The case of Helen Keller is one
demonstration that they can be measured. Anything whatever that makes a
difference in the way different individuals act is conceivably
measurable, although it may not at the present time be capable of exact
calculation because it has not been worth anybody’s time and effort to
undertake to measure it.
To repeat, and possibly to make the preceding paragraphs more clear, let
us recapitulate the different mental qualities to which reference has
been made.
First, mental _capacity_. This is what the individual has inherited. It
is the size of the tank into which sensations, perceptions, all that
makes up the sum of knowledge, are poured throughout his life, by his
education and his experience. While this capacity in the case of any
individual can doubtless be measured, it is not necessary to measure it
precisely but merely to determine whether it is large enough for the
purposes in view.
Second, mental _ability_. This is the sum of experience and education
within the limits of the individual’s mental capacity. It is represented
by the individual’s ability to express himself in speech or action in
the performance of any one of a number of specific acts. This mental
ability can be quite definitely measured, and the possession of a
certain degree of mental ability demonstrates the possession of a mental
capacity greater than the ability which the individual has already
reached.
Third, _acquired knowledge_. It is not the purpose of tests of mental
capacity to measure acquired knowledge, although for many purposes it is
desirable to measure the individual’s acquired knowledge _in addition_
to his inherent ability, and in a still larger number of instances the
most practical way of arriving at a fairly accurate estimate of an
individual’s ability involves, among other tests, an examination into
the extent of the knowledge which he has acquired through observation or
training along lines definitely related to his particular occupation or
pursuit in life.
The ordinary and standardized school and university examinations,
civil-service examinations, etc., which have long been the accepted test
of the individual’s ability, do not, and do not purport to, measure
anything more than this last item, that of acquired knowledge. But while
certain gross dimensions of individual capacity may be roughly estimated
from the results of a written or an oral examination based entirely upon
the subject’s stored-up knowledge, it is a matter of common knowledge,
and almost every reader will be able to furnish examples out of his own
experience, that such tests are frequently totally misleading. Professor
Terman has reported on a comparison of the results of civil-service
examinations for policemen and firemen in a California city with
scientific tests applied to the individuals who successfully passed the
civil-service examinations. The results were in many instances
astounding. Men of such low mental capacity that they might almost be
classed as feeble-minded were found to have passed with a fair degree of
satisfaction the simple knowledge and physical tests set up by the city
and to have obtained appointments to these responsible posts as
guardians of the city’s property and lives.
While it is, therefore, the object of scientific mental tests to exclude
as far as possible the acquired abilities resulting from education and
environment and the knowledge that has been stored up through
observation and training, it is found in practice that for all ordinary
purposes it is sufficient to measure a complex of native and acquired
abilities. The purpose of these tests is, in short, to discover what the
individual is actually able to do, regardless of the source of that
ability, provided, however, that the test of ability is so devised as to
make a clear distinction between mere feats of memory and the actual
exercise of original thought.
Now, it must be obvious that for the measurement of anything so complex
and multi-dimensioned as the human mind, no single test or scale can be
established. One cannot measure the power of visual perception, for
example, by the same scale that is used to measure attentiveness or
initiative. As a matter of fact, psychologists no longer attempt to
classify human abilities as narrowly as was once the popular practice.
It is almost impossible for even an expert psychologist to be sure he
knows just what qualities and all the qualities any particular test
measures. This is because modern psychologists no longer group reactions
into general functions such as memory, attention, reason, etc., but
simply describe accurately the stimulus given and the conditions under
which it was given and then describe just as accurately what the
reaction is. The test may be built up, for example, to measure ability
to recognize and classify words, but it will also depend upon ability to
read the directions, ability to attend closely to horizontal and
vertical lines and upon many other correlated abilities. Any test may
measure primarily a particular mental dimension or ability but it is
quite certain that the resulting score will be influenced by numberless
other factors than the one that the examiner is most interested in
measuring.
But since one of the very best tests of intelligence is, of course, the
degree to which one is able to profit by social contacts and the breadth
and variety of the individual’s stored-up impressions, these extraneous
or collateral qualities, which every test also more or less successfully
measures in addition to the particular quality or mental dimension under
direct examination, furnish useful data in arriving at a conclusion
which is, after all, the main purpose sought, as to the individual’s
actual abilities and potential powers.
In order, however, to get at a really useful record of the mental
capacity of an individual, we must apply a variety of tests and out of
the sum total of the results of these tests we are able much more
accurately to gauge the degree of possession of the qualities for which
we are seeking than could possibly be done by any single test, no matter
how skilfully constructed. Here again science confronts the popular
human demand for a panacea. But just as in medicine only the quack
offers a cure-all, so, in other fields, science has no single standard
to offer by which all results in a given field may be accomplished, and
psychology cannot now or at any time in the future pretend that by a
single method or a single measurement mental capacity can be gauged.
To come back to an analogy used in a previous chapter, you cannot
measure all the qualities of an automobile with a ten-foot rod. Your
ten-foot rod will tell you whether the wheel base is 120 inches or more
or less than that. It will not tell you how much above or below 120
inches. If it be necessary for you to know that, you must provide
yourself with a longer or more minutely graded measuring implement; but
because the ten-foot rod does not at a glance disclose to you all that
you wish to know about a particular automobile, you do not, therefore,
either discredit the ten-foot rod as a measuring implement or declare
that the automobile cannot be measured except by the unaided human eye.
The limitations of the ten-foot rod are perfectly obvious to you; and
so, too, are the complexities of the automobile, which require a variety
of instruments and tests for their proper gauging and measurement. So
before you undertake to form a judgment as to the ability of a
particular automobile, you either measure it yourself or, as a matter of
practice, you have it measured for you by a competent engineer. You do
not necessarily inquire, if you have confidence in the engineer, as to
precisely what dimensions and what materials he found in every part of
the car, but you respect his conclusions, knowing that they are based
upon the most precise and accurate measurements possible with the aid of
such instruments as science has been able to devise, and you are
satisfied that the conclusions form an accurate estimate of the
machine’s qualities.
The engineer who sets out to measure an automobile in all of its
capacities and powers must provide himself with tachometers for
measuring the engine’s revolutions, dynamometers for testing its
tractive force, micrometer calipers for gauging the bore and the stroke,
thermometers for measuring its temperature, galvanometers for testing
its magneto and battery, and hundreds of other instruments, the readings
of which must be assembled and studied by means of complex, comparative
mathematical formulas before he can tell you what a particular
automobile will do.
The human mind, it must be apparent to every reader, is not less complex
than the automobile. On the contrary, it is infinitely more complex and
subject to an infinitely wider range of variations. As has been pointed
out above, it is not necessary for practical, every-day purposes to
measure every possible variation and every one of the infinite number of
dimensions of any human mind in order to ascertain the individual’s
ability to succeed in the ordinary pursuits of life. But even in our
ordinary, every-day affairs and contacts, in the simplest forms of
employment, there are called into play such a number of different sorts
of ability and mental power that there must be applied, if one is really
to know of what a particular individual is capable, a large variety of
tests of different kinds for measuring different powers. And for the
mental measurement of individuals whose work calls for the highest
development and capacity, a still larger variety of tests must be
applied.
It is not always possible—in fact, it is extremely difficult—to devise
tests that do not to some degree measure the mental content resulting
from education and experience, in the effort to measure the mental
capacity which limits and controls one’s education and experience. The
qualities that determine capacity are inherent in the individual. One is
born with them or is not born with them. In their whole infinite variety
they are not all possessed by any one individual, and the particular
grouping of mental qualities which any one person inherits is probably
not possessed by any other person living or who has ever lived. Yet
while individuals differ so completely that it can truthfully be said
that Nature never cast two persons in the same mold, yet there are
qualities possessed by all intelligent persons, the simpler and more
elemental expressions of which are absolutely essential to intelligent
life and existence, and these can be so grouped, classified, measured,
and standardized as to provide a scale whereby the inherent capacity
with respect to these important and essential qualities may be
determined equally in the case of the totally illiterate, untrained
labourer or artisan and the highly trained, educated product of a
university postgraduate course.
As a matter of practical, every-day common sense, one does not expect to
find, nor does one find, except as a rare exception, an individual
engaged in menial or purely physical labour who is endowed with inherent
mental capacity comparable to that of the university graduate. A person
possessing such capacities moves out from the ranks of labour in spite
of educational handicaps; the history of American business and industry
is full of the romantic stories of men who have achieved success as
organizers and administrators, though in many cases absolutely
illiterate. Properly applied psychological tests would pass over all or
nearly all of the acquired knowledge of such individuals about their
particular business and related matters, and neglect also, the bulk, at
least, of the acquired knowledge of the university man, and so compare
merely what might be called two naked brains, the native intelligence of
each being the only thing to be measured. As has been pointed out, it is
difficult or almost impossible to devise tests that entirely strip the
layers of acquired knowledge from the raw mental powers beneath them,
but for the practical purposes of the application of psychology and
psychological tests in the affairs of every-day life, this can be done
within a reasonable percentage of error.