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 (and by inference the greatest capacity for further development along similar lines) 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.