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.