This book is written neither for the super-skeptical nor the ultra-credulous. It makes no pretension to infallibility, nor does any scientifically trained psychologist pretend that there has yet been evolved a method of measuring every dimension and capacity of the human mind beyond the possibility of error. The methods described in this book are the fruit of years of experiment, research, and practical application of the results of experiment and research, and are designed to reflect the development of the science of psychology in its application to mental measurements as closely as it is possible to do so within the limits of a single volume written primarily for the reader who has no special scientific training along psychological lines.
The reader who is not prepared and willing to examine facts and at least to take all the ascertainable facts into consideration before forming his conclusions is not likely to be interested. The scientific method of character analysis or mental measurement is based upon the comparison of the largest possible collection of ascertained facts. Guess work has no place in it. Psychology has small dealings with intuition and instinct nor is it in any way derived from magic or concerned with the occult. There are no unfathomable mysteries. There is no fact about the operation of the human mind which cannot be subjected to scientific investigation and measurement by any intelligent person. The scientific method requires that every conclusion must square with the results obtained by the experimental application of all related facts or be discredited as worthless. Theories have no place in science, except as something to be disproved if possible, and a single fact which does not square with any theory disproves the theory.
The scientific method of mental measurement has passed the theoretical stage. It has squared with the facts wherever it has been intelligently applied. It has been demonstrated in a wide range of business and industrial applications, in education and in its use in determining the qualities and fitness of officers and men in the Army and Navy. What it offers is the shortest, simplest, and most accurate means available of determining human capacities and qualities.
Professor Terman has admirably summarized the advantages of the scientific method of testing intelligence, as follows:
“1. It gives us a universal standard of comparison. The result is absolutely uninfluenced by the general intellectual level of the group with which the subject to be rated happens to be associated. It is like measuring the height of a house instead of estimating it by comparison with the height of surrounding buildings.
“2. It multiplies enormously the significance of mental performance. It does this by making fine distinctions which would be overlooked by the method of offhand judgment. It is like placing a smeared glass under a microscope and discovering that the smear is a complicated network of organic matter.
“3. The test method is objective; that is, free from the influence of personal bias. It gives approximately the same verdict to-day, next week, or next year. It does not change its opinion. More important still, the verdict will be approximately the same whoever makes the test, whether a relative, a stranger, a friend, or an enemy, provided only that the rules of procedure be rigidly followed.
“4. The test result is little influenced by the subject’s educational advantages. In this it differs greatly from offhand judgment, which so easily mistakes the results of schooling for real intelligence. The test method probes beneath the veneer of education and gives an index of raw ‘brain power.’ For example, a young woman who had been stolen in early childhood by gypsies and had spent her life with them was given the Binet-Simon intelligence test. She had never attended school a day in her life and had only learned to read by bribing a little school girl to teach her the alphabet; yet she made a higher score than the average found for two hundred high school pupils who were given the same test.
“No wonder,” Professor Terman concludes, “mentality tests have acquired such a wide vogue in the ten years since Binet gave to the world the first successful intelligence scale. In that time they have demonstrated their usefulness in the study of the feeble-minded, in the grading of school children, in determining the mental responsibility of offenders, and in the selection of employees. Their largest and most useful applications have been in the mental classification of men in the United States Army.”