# Page:Popular Science Monthly Volume 81.djvu/459

year of college or professional school in my hundred individuals this figure is, on the average 9, three fifths of the individuals showing sums of from 6 to 12 for column 2 of Table 3. This average result of 9 may be expressed as a coefficient of correlation or correspondence, such as is in customary use to measure resemblances of various sorts. It is equivalent to a correlation of over.60. This means that a person's interests in the late elementary-school period resemble, in their order and relative strength, the constitution of interests which he will have eight years later to the extent of six tenths of perfect resemblance. For the coefficient of correlation is a magnitude running from ${\displaystyle {{\ce {-}}}}$ 1.0, which would be the coefficient if the sum of differences was 24, through 0, which would correspond to a sum of differences of 16, to ${\displaystyle {{\ce {+}}}}$ 1.0, which would correspond to a sum of differences of 0. A sum of differences of 8 means a resemblance greater than half of perfect resemblance, as the reader expert in the mathematics of probability will realize. The sums 12, 10, 8 and 6, in fact, mean coefficients of resemblance or correlation of +.38, +.55 +.71, and +.83, respectively.