Variability (e.g., among people, objects, organizations, nationalities) is what arouses a scientist's curiosity and impels him or her to search for its causes. No wonder that Galton (1889), whose work has served as the major impetus for the study of individual differences, expressed his astonishment at statisticians' failure to study variability: It is difficult to understand why statisticians commonly limit their inquiries to Averages, and do not revel in more comprehensive views. Their souls seem as dull to the charm of variety as that of the native of our flat English counties, whose retrospect of Switzerland was that, if its mountains could be thrown into its lakes, two nuisances would be got rid of at once. (p. 62)

i = }:(X - X)2 };x2 x N-l -N-l (17.1)


The information necessary for the calculation of the variances of Y and X is given at the bottom of Table 17.1, as are results of intermediate calculations and the answers. We begin by calculating the sum of squares. Using IY and IY2 from Table 17.1, and applying (17.2):

}:y2 = 903 _ (l~~)2 = 70.95 Applying now (17.1),

Calculate the variance of X and check your answer with the one given at the bottom of Table 17.1.