Read Ebook: Measure Your Mind: The Mentimeter and How to Use It by Stockbridge Frank Parker Trabue Marion Rex

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The intelligent reader has by this time begun to see for himself some of the possibilities opened up by the use of scientific mental tests, and to perceive their applicability in a wide diversity of fields. In later chapters specific examples of such applications are given in detail, and suggestions offered for still other uses of the tests which are contained in this book.

The general purpose of psychological tests is to determine how individuals compare with one another in mental capacity, or with standards based upon the capacities of individuals known to possess certain qualities. Thus, it may be desirable, as it frequently is, to determine the relative abilities of the individuals of a certain group, like a school or college class, clerks employed in a similar form of work, a number of applicants for a certain position for which only the most capable among the candidates is desired, or the soldiers of a particular company or regiment. What is required here is a method of grading these individuals with reference to one another, by means of tests which need not necessarily have any relation to any external standard of mental perfection.

That is about the process that a man engaged in the automobile trucking business would use in determining which one of the cars he has available is best adapted for a particular piece of hauling that is to be done. He wants to know which of his cars he can rely upon for any one of many different sorts of service, but he particularly wants to know all the time which of them are worth spending money on for repairs and improvements and general overhauling and which are either so poorly constructed in the first place or so hopelessly out of repair that it is cheaper to scrap them than to spend any more money on trying to make them fit for service.

Now, the man who operates a fleet of automobile trucks does not stop when he has made a comparison of the vehicles in his garage with one another, but is constantly comparing the performance of each with standards established by other cars, machines of different makes, and with new machines. There exists, and he is constantly conscious of its existence, an ideal standard of performance for automobiles to which his cars must conform as nearly as possible if their service is to be satisfactory.

So, in measuring human capacity, it is not enough to compare the individuals of a group with one another, though this is essential and for some purposes temporarily sufficient; there are available standards based upon the actual achievements of individuals of known capacity by which the mental powers of any and all individuals may be gauged. It will readily be seen that the employer of a number of persons--engaged, let us say, in some specific mechanical or clerical operation--needs to know not only whether some of these are capable of being trained to do better work and some so incapable of further training that it would be cheaper to discharge them and fill their places with more intelligent persons, but also to know how any particular group of employees compares in average intelligence and how each one of the group compares in individual intelligence with the average or higher-than-average capacity of those outside of his own particular business establishment who are engaged in similar work.

This is a matter of dollars and cents to the employer. If he can obtain a standard that is universal or nearly so, that tells him, in fact, what all of the employers in his line of business have found to be the average or the limits of mental capacity possessed by workers of a particular class, then he is in a position to determine whether he is getting equally good service for the wages which he pays as is obtained by other employers requiring similar service.

To illustrate concretely: in an office employing twenty stenographers on correspondence, it is not only necessary for the employer to know which of these stenographers is the most competent and which the least and whether the less competent are incapable merely because they are beginners or because they lack the necessary mental capacity ever to become competent. He should also be able to measure the mental capacity of the entire group by some standard based upon the performance of thousands and tens of thousands of stenographers of known degrees of ability. He may discover that the most competent of his entire staff is only as capable as the average of good stenographers everywhere. Obviously, his business is handicapped by having a stenographic force which is inferior in capacity and, consequently, in accuracy, speed, and other essential requirements, to the average of stenographic office staffs in business generally. Once this has been determined, the intelligent employer will proceed to replace the stenographers who are incapable of improvement, as indicated by the tests applied, with stenographers who respond to the standard tests with a score well above the average.

So, too, with the teacher. It is comparatively easy for the teacher to classify his or her pupils into bright, stupid, and mediocre, through observation alone. What is more important, however, is to determine several things about each pupil which observation alone does not tell. Are the stupid ones really stupid or merely inattentive? Have they the necessary mental capacity to perform the assigned work of the class or are they simply lazy? Few teachers can answer this question; none with any degree of accuracy without the application of scientific tests of mental capacity. Are the bright children really bright by comparison with other children of the same age and school grade or do they merely shine by contrast with the dull members of the class? This question can by no means be answered accurately except by the application of mental capacity tests. In another chapter some of the concrete applications of mental tests in education are described at length. The point to be emphasized here is that the measurement of the mental capacities of any group should be based upon standards that will not only determine the relative capacities of the members of the group but will, at the same time, compare them all with standards that reflect the known average and maximum capacities of all others of similar age and environment.

The purpose of these tests might be summed up somewhat as follows:

It requires no special argument to point out how a general application of tests that disclose actual mental capacities might profoundly affect our judgment of men of all classes and walks of life. Were it possible to ticket and catalogue the whole human race in accordance with the capacity of each individual as disclosed under properly devised psychological tests, we would no longer permit the superficial absence of polish and taste to blind us to the inherent powers and capacities of the self-made man, nor, on the other hand, would we be so ready to assume that the well-dressed, fluent talker, no matter how prepossessing in appearance and manner, was necessarily able and worthy of confidence. Likewise, once such a classification became universal, it is conceivable that many business men and others who are prone to criticize the universities and their products would be more tolerant of the recent graduate, whose mental capacity is in no wise reflected by the particular variety of contents with which his mind has been filled in college.

Besides the application of scientific mental tests as already indicated, in business and industry and in education, by the employer or the teacher, there is another and important use to which standardized tests, based upon determined capacities of groups and individuals of known ability, may be put. This is the use of such tests by the individual upon himself for the purpose of determining his own mental capacity in a particular direction or of a particular kind as compared with the mental capacity of others. The man or woman bent on self-improvement or advancement may thus, within certain limits, assess by the application of standardized tests his or her own mental quality and capacity.

Again it is unnecessary to point out the advantage to the young man or young woman endeavouring to decide upon a career or to determine what particular course of study to pursue or line of business to enter, in being enabled to obtain an accurate gauge of his or her own qualities, powers, and limitations. Taste and inclination are no safe guides to life unless there is coupled with them inherent capacity for the competent exercise of the faculties which make the gratification of one's individual tastes and inclinations possible. Thus it may be that the individual's inclinations and tastes run strongly toward music, toward art in any of its various forms, but that physical and mental inhibitions, the presence or absence of which may be readily determined, make it impossible for the possessor of such tastes to hope to be able to perform creditably the acts which a successful artist or musician must perform.

Properly devised and applied psychological tests may conceivably disclose the existence of mental powers and capacities unsuspected or neglected because overshadowed by strong inclinations in other directions; early knowledge of the possession of such capacities may easily direct their possessors into fields in which they can thrive and prosper and achieve far greater happiness and contentment than would ever be possible through a lifetime of striving to do that for which they are not fitted by inheritance.

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 co?rdinated 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.

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.

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.

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.

To test or measure mental capacity or any of the dimensions and powers of the human mind, two preliminary steps are necessary.

First, it must be determined what particular powers or qualities of the mind it is desired to measure.

Second, there must be prepared a standard or scale that is, primarily at least, adapted to the measurement of those particular qualities.

While it is, in practice, as has been heretofore pointed out, impossible entirely to segregate a particular mental quality or power from all the other abilities and capacities possessed by a particular individual, it is possible to select certain characteristics or abilities which, by the degree of their presence or absence, give a fair index of certain mental dimensions or capacities, and to devise tests that, when taken together, will measure these "key-abilities" and so reflect the general ability and capacity of the subject. The standards by which the results of such tests are gauged must necessarily, therefore, be such as have been shown, by experiment and experience, to give the closest possible measurement of the individual's ability in these particular directions, by enabling the examiner to compare each subject's performance under the test, or series of tests, with the records made under precisely similar tests by individuals and groups of known ability.

Mental capacity tests may be devised that will measure certain mental qualities of an infant who has not yet learned to talk, and by thus providing a comparison between this particular child's capacities and the average of children of the same age, enable parents and physicians to determine in what direction efforts looking toward its mental development may most helpfully be undertaken. Thus we may test the infant's power of observation and perception of shapes, of colours, of sounds and familiar objects before it is able to talk, measuring these by standards derived from experience with similar tests applied to a large number of healthy, normal infants, and by this means determining whether the subject is above or below the normal average for its age and if so in what respects.

The simplest way to measure the capacity of a circular tank is to pump it full of water and then measure the water as it is drawn off. But it would be absurd to contend that because there has never been any water pumped into the tank it is therefore impossible to determine how much water it would hold. And what the Doctor of Philosophy has got out of his university course is comparable to the water in the tank. The university may have assisted, and if its faculty were competent undoubtedly did assist him, in discovering earlier in life than he otherwise would have discovered the actual capacity of his mental tank. But there are probably as many men of equal mental capacity whose mental tanks have never been filled with the particular kind of intellectual fluid that the Ph.D. carries about with him, whose capacity there is no other means of measuring than by the application of mental tests based upon the known capacities of Doctors of Philosophy.

The process of measuring the human mind is, indeed, precisely like the process of measuring an automobile by an engineer, as was pointed out in the preceding chapter. Back of the tests that are applied to the automobile to determine its abilities and capacities there must lie a mass of very definite, exact knowledge of all automobiles or all types of automobiles already in existence and whose capacities and limitations are already definitely known. It is of no service to ascertain that the engine cylinders are of four-inch bore and that the piston has a six-inch stroke, unless it is well known what the possession of a given number of cylinders of that particular bore and stroke signifies as to the ability or capacity of an automobile engine. That knowledge has been acquired by the observation and measurement over a period of years of the performance of many automobiles of varying cylinder sizes and number of cylinders, and the comparison of each size and type with all the others.

Similarly, it is of no service to apply a test of any kind to a human being unless we have, in the first place, determined just what particular abilities or capacities we want to measure, and, in the second place, possessed ourselves of knowledge as to the significance of these capacities, after they have been measured.

Here, again, the reader should keep constantly in mind the warnings set forth in the preceding chapter and try to think of mental abilities and qualities not as detached, separate, sharply defined parts of a mental whole but rather as qualities so intermingled and connected by an infinite number of attachments to all the other mental qualities and abilities that no one particular ability can be measured separately or even positively delimited by any sort of test. Even if this could be done in the case of one individual, the process would have to be repeated in each separate, individual case, as in no two human beings is there found exactly the same combination and correlation of the manifold manifestations of conscious sensation and thought that together make up the human intelligence.

But having determined just what qualities and abilities it is desired to measure, we must set up a standard of measurement by which to compare the indicated ability of each individual examined, or we shall have nothing as a result of our test but a mass of information, of the significance of which we cannot possibly be aware. This standard, for some purposes, may be merely a composite record of the performances of a particular group or class examined simultaneously and under the same conditions. That is to say, if all that is required is to determine which individual of a group has the greatest ability in certain directions then all that is necessary is to apply a test that will give a comparative measurement of the intelligence of this particular group. But if the purpose is to ascertain how a particular individual, or the average of a group of individuals, compares in particular kinds of capacity with the average or the most highly developed persons of the same status, education, occupation, or age, then the standard by which the subject must be measured must be one derived from the observation and measurement of the mental capacities of as large a number as possible of individuals engaged in all sorts of occupations and of all degrees and grades of educational attainment. And even where the purpose is merely to determine the relative qualifications and capacities of a particular limited group, it is as a matter of practice desirable, it might almost be said necessary, to compare the performance of each individual of the group with a standard previously fixed and determined as a result of a much broader series of observations and experiments than can be made within the limits of any group to which it is practicable to apply any given set of tests as a whole.

This is true for two reasons. First, without such an outside standard of comparison all that is determined by the application of even the most carefully devised tests to any group is that certain individuals are more and certain others are less able in particular ways than the average of the group. The net result is of service, but of nowhere near the service of a record of the same individuals' performances graded in accordance with their approach to conformity with a universal standard. For example, one might take two, three, or a dozen automobiles on a speedway and quite readily determine which was the fastest and which the slowest, but unless one were possessed of certain standards of measurements that in themselves have no relation whatever to automobiles, the net result would be of little consequence and of no value whatever in comparing any one of these cars with another automobile that had not taken part in the particular test. In this case, two standards are requisite, namely, distance and time. The length of the course must be definitely ascertained. The time required for each automobile under test to cover the course must be accurately recorded.

Now we have a record of performance that compares at all times with universal standards. If we add another automobile to the group we do not need again to run all the cars, including the new one, along the speedway to determine where the added member of the group ranks with reference to the others; we can apply to it alone a test based upon the universal standards of time and distance with which we have already compared the others, and the new one falls instantly into its proper rank among its fellows. So, too, we are enabled by this means to compare any member of the group with any automobile anywhere in the world, the performance of which has been gauged by these same universal standards of time and space, and we are thus able to tell, not only how each particular car ranks with reference to the limited group of cars, but how it ranks with reference to all cars of all kinds or of a particular type so far as these have been tested by the universal standard.

So in testing groups of individuals as to their intelligence or mental capacity, the use of universal standards of comparison makes the relative grading of the members of the group with reference to each other just as easy and simple as though the only standard were that of the group's collective performance, and at the same time furnishes a record of the performance of each individual member of the group by which he or she may be readily compared with the members of any new group to which he or she may be at some subsequent time attached, and at all times with the general run of men or women of the same or differing social, economic, vocational, or educational status.

It is in the determination of these universal standards and the preparation of tests, the results of which indicate the individual's relative approximation to these standards, that the scientific training of the psychologist comes principally into play. Rough standards for testing the more obvious mental capacities might be set up by any intelligent person who would take the pains to collect the essential data. These standards would not, however, be universal unless they were based upon research and experimentation covering as broad a field as that in which the psychologists have been working for many years. Nor would they, except by accident, be as simple and as accurate as the universal standards compiled by scientifically trained persons. For just as the average untrained individual cannot form an accurate or even an approximately accurate estimate of another person's character and abilities by observation alone, so persons untrained in the study of the human mind are prone to be misled by the obvious and to lay undue emphasis upon external indications which do not, as a matter of scientific fact, actually signify what they are popularly believed to indicate. The scientific psychologist's training enables him to eliminate to a large extent the non-essentials and to include, in the establishment of standards of mental measurement and the preparation of tests or methods of applying these standards, many facts which, to the untrained mind, do not at once present themselves as important elements.

Even in the simplest of mechanical operations every workman knows that it is not safe to trust to the accuracy of homemade measuring implements. In the absence of a try-square made by a responsible manufacturer in conformity with the universal standard right angle, even the most expert carpenter will refuse to run the risk of error until he has either obtained a new standard from the hardware store or by the application of geometrical science and the exercise of careful and painstaking technical skill constructed for himself a new try-square that conforms, without the variation of a hair's-breadth, to the universal standard to which he must work. Still less would a good machinist undertake to gauge the close tolerances of an automobile bearing with a homemade micrometer. He knows it is not sufficient merely to have a perfect fit of this particular bearing, which might be worked out by rule of thumb, but that it is essential that the dimensions of the bearing, down to within a thousandth of an inch, must conform to the universal standards for automobile bearings, and that the best implement with which to test the degree of conformity to the universal standard is the standardized micrometer, prepared by specialized methods and produced only by the exercise of highly trained technical skill. Once given such implements of precision, any good workman can readily apply all the scientific intelligence that went into the devising of the standards and the preparation of the methods of applying them.

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