To this argument Pearson might reply that he had not overlooked the question of variation in the deviations from one age to the next for he has a footnote in which he states regarding the Jaederholm data: “There are, however, relatively little differences in these mental age standard-deviations of the normal children beyond what we may attribute to the effect of random sampling” (_164_, p. 46). In this respect, then, the Jaederholm data differ notably from Terman's data obtained with random groups with the Stanford scale and, as I shall show, from data obtained by Goddard with the 1908 Binet scale, the two largest groups of Binet test data which have been collected. Even with the Jaederholm data on efficient school children, although the largest difference between the standard deviations of different age groups is only about twice its probable error, it is notable that 24 of his 39 7-year-olds are included within an interval of the middle year of tested age, while only 9 of his 35 11-year-olds are included within the same middle year interval. Taking Goddard's data for the 1908 scale for the separate ages from 5-11 at which probably the factor of selection for his groups may be neglected, I have calculated the standard deviations from his Table I and find them as follows: ────────────────────────────────────┬────────────────────────────────── │ Life-Ages ────────────────────────────────────┼────┬────┬────┬────┬────┬────┬──── │ 5 │ 6 │ 7 │ 8 │ 9 │ 10 │ 11 ────────────────────────────────────┼────┼────┼────┼────┼────┼────┼──── Standard deviations in Mental Excess│1.10│.98 │.93 │.99 │1.04│1.23│1.19 or Deficiency │ │ │ │ │ │ │ ────────────────────────────────────┴────┴────┴────┴────┴────┴────┴──── The differences between the deviations for ages 7 and 11 or between ages 8 and 10, are more than three times their standard errors, so that we would not be justified in assuming that the standard deviations of the separate ages measured in terms of years of excess are equivalent. There seems to be a tendency for the deviations to increase, at least from age 7 to 10 and 11.