Abstract
The fact that the decline of intelligence occures with the passage of years has been established by many researehers through imvestigating intelligence test abilities. It has also been established that this decline does not occur at the equal rate with each subtest. About the causes of this decline a few explanations have been advanced. Some contend that there are two kinds of mental abilities, one a negative capacity and the other an acquired ability, and it is the former ability that the age factor influences more strongly.
Others insist upon the fact that the physical function declines with age, that the mental functions, such as speed, alertness, and so forth, which have close correlations with that function also decline.
The previous investigations were conducted with normal citizens of rural or urban residents or with those of homes for the aged or hospitals. Our subjects differ from those of the previous ones in that they belong to the leadership class and are acting vigorously as local leaders.
The subjects are 284th decaders, 665th decaders. and 145th decaders, ranging from 40 years to 69 years.
They are now commissioners of the local boards of edudtaion (towns and villages).
Koga's Intelligence Test, Form II was given to those subjects. And the results were analysed as to whether the intelligence declines with the progress of age or not.
Varied declines of each subject ability were compared and closely investigated. As the samples are very small, the t-test, using the small sample formula, was tried to determine the significance of the mean differences from decade to decade.
Significant decline of intelligence from the 4th to 6th decade cannot be found. There was no significant difference among the declines of the subtests abilities within each decade.
From the above results, we can conclude that the decline of intelligence does not appear in our selected samples of the leadership class in education at the age of 6th decade. Thus the results of this investigation are negative.
Whether such an absence of decline of intelligence is due to the innate endowment or to circumstance is not clear. If it is due to the endowment or superiority of intelligence. Thurstone and others' theofies...more rapid decline of intelligence among the brighter than among the dull...must be rejected, and if it is due to the circustances...using or not using, or experience...we can find many snpportillg and opposing viewpoints among the previous investigators. We must investigate much more samples of the same and different kinds before we can explain the cause of the present result.
