Page:American Journal of Psychology Volume 21.djvu/497

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Scores Reduced to Single Variables by Allowance for Examples wrong
 * Individuals
 * Sex
 * First
 * Second
 * Third
 * Fourth
 * Fifth
 * Sixth
 * Seventh
 * A
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The relation of the amount of improvement to initial ability in any practice experiment is of great interest because it gives evidence bearing upon the fundamental problem of the relative shares of original nature and environment in determining the achievements of men.

It has been shown that in the case of educated adults the relative (that is, percentile) differences amongst educated adults in the ability to multiply mentally a three-place number by a three-place number are left unreduced by submitting all the individuals to equal practice.

The differences amongst individuals in the ability to add seem to be due in larger measure to differences in environmental influence. For equal practice does here reduce a little the relative or percentile differences within our group. This will be seen by comparing the relative variability of the group in the seventh practice period with that in the first, or by calculating the co-efficient of correlation between initial ability and percentile improvement. The proportions for highest and lowest individuals, next to highest and next to lowest are:

In first practice period In second practice period ist 19th .45 3.36 nd 18th .25 1.99 rd I7th .92 1.87 th 16th th I5th .82 1.46 1.62 1.46

The correlation between initial ability and percentile improvement is negative, roughly #

There is, of course, no essential conflict between this result for addition and the opposite result for mental multiplication with two