The initial plan of the experiment was to compare the performance of a group of college students with that of a group of the youngest school children who would be capable of the performance required in the experiment. We judged that 4th grade children would meet these specifications. Because our judgment turned out to be excessively conservative, we subsequently added a group of 3rd grade children. The composition of the three groups was as follows: Group I, 20 university under¬graduates, 7 male and 13 female. Group II, 17 4th grade children, 10 years i 5 months of age, 8 male and 9 female. Group III, 15 3rd grade children, 9 years 1" 5 months of age, 7 male and 6 female.
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