Once, however, tests have been applied to the supposititious thousand expert engineers, and the performance of each of them in each test has been given its proper place in the scale, and an average struck, there has come into existence a preliminary standard; which, however, before being offered for general use in the testing of engineering students and others, must first be tried out by experimental application on as many individuals and groups as are available, and their performance with reference to the standard checked up by all other means available. It may be, and quite frequently is, the case that this preliminary try-out of a standard results in the elimination of some of its elements, the modification of others, and the necessary preparation of a new series of tests based upon the altered standards. But in this fashion, in the course of time and as the result of the combined effort of many trained minds, there is at last set up a standard which is substantially universal in its application, and by which it may readily be determined whether or not any particular individual possesses the mental capacity and particular abilities that have been found to be necessary if he is to develop into a competent engineer.
As psychological tests are more and more widely applied and there is consequently accumulated an increasing volume of data which can be collected, classified, and compared, standards become either more firmly established as a result of experience or subject to modification in the light of the wider range of knowledge. In science nothing is final. What psychology offers to-day is a method of mental tests, the soundness of which in principle is unchallenged, though the application in detail of these principles is subject to constant improvement and refinement.
CHAPTER V
DIFFERENT TYPES OF MENTAL TESTS
The character of any mental test or series of tests is determined primarily, of course, by the purpose for which the test is applied, and, secondarily, by the known or obvious mental limitations of the individual under examination.
Mental tests thus classify themselves, in the first instance, into as many different classes as there are specific purposes to be served by their use, particular kinds or classes of mental ability and capacity to be ascertained, or degrees of previously known mental limitations. Each one of these classifications cuts across all other classifications at some point, so that it is, as a matter of practice, impossible to tabulate or catalogue mental tests in such a way as to separate them into sharply defined or permanently detached groups or classes.
Broadly, all mental tests subdivide at first into tests devised for use with persons of normal mental capacity and development and tests for intelligences that are not fully developed. This is, perhaps, the chief permanent and fixed classification of intelligence tests that can be made, for in a group of tests for the sub-normal mind would be included the entire series of tests adapted for the examination of the mental powers of children of all ages, from earliest infancy to maturity. In fact, the standard method of rating or grading adults of undeveloped or sub-normal intelligence is to classify them by their mental age as compared with the performance of normal children of the same age.
Thus, a man or woman of twenty-five who is able to make a high score in tests which are passed successfully by normal children of eight, but who fails when subjected to tests which a normal child of ten should pass easily, is rated approximately as of mental age nine.
Cutting across this classification is the arbitrary classification of tests adopted in the psychological work of the United States Army, in which every officer and enlisted man is classified as to his relative intelligence by means of scientific mental tests. The Army tests are of three principal kinds. There is a series of tests, known as the Alpha, designed to measure the intelligence of individuals who can read and write the English language. For those who are either illiterate or whose ability to read or write is confined to some language other than English, there is the Beta series of tests. These may register as high a degree of intelligence as the Alpha tests; the results are merely not expressed in terms of the English language. The third classification in the Army is the individual tests, applied to those who fail to make a satisfactory score under either the Alpha or the Beta tests. This is, in its Army application, a system of tests for the sub-normal adult intelligence. Thus the broad classification first set forth above, in substance actually holds in the classification of the Army tests.
Under each of these two broad classifications, and particularly under the first (since in general, every-day practice it is of little service to undertake to analyze minutely the capacities and limitations of the sub-normal mind except in the application of these tests to growing children) there are many possible subdivisions of mental tests, based upon the particular mental qualities which it is desired to measure.
First and most useful generally are general intelligence tests, which must usually be subdivided into a series of related tests. Then, for varying purposes, such as the examination of candidates for particular classes of employment requiring special ability or capacity, there may be applied speed tests, accuracy tests, perception tests, coördination tests, memory tests, mathematical tests, and a wide variety of others. These are tests which primarily measure the subject’s ability to perform certain specific acts under pre-determined conditions, the determination of capacity in excess of that actually demonstrated under test depending upon the facility and accuracy with which the subject responds to the conditions of these tests. Of course, every scientific mental test is based upon the performance of certain acts, since it is only through action of some sort, whether by speech, writing, or the performance of a manual operation, that any one is able to express his mental ability at any time.