38 Aubrey Lewis 



matter how the factors are named or interpreted, it is evident 

 from Bahnsky's data that the same tests measure different 

 abihties in the adult at different ages. Birren hkewise by 

 factor analysis of data obtained from the Wechsler Bellevue 

 Scale administered to subjects between sixty and seventy 

 years of age, found that four factors could be extracted 

 from the intercorrelations: they were — verbal comprehension, 

 closure (non-verbal organization of visual perceptual 

 material), memory, and perhaps induction. 



The greater scores usually attained on tests requiring verbal 

 comprehension depends mainly on the store of verbal in- 

 formation retained by ageing persons, while ability to acquire 

 fresh information and face fresh situations diminishes. 

 "It seems reasonable that the age of optimum learning and 

 the age of maximum stored information are not coincident, 

 and do not correspond to the age of maximum scores on our 

 intelligence tests". It follows that a scale like the Wechsler 

 Bellevue needs to be docked of some items and amplified with 

 some others if it is to cover the mental abilities of ageing 

 people and permit comparison of one elderly person with 

 another or with a standard population of the same age. 



It seems clear from the many studies of decline in intelli- 

 gence in ageing people that a wide range of tests and a series 

 of longitudinal studies of the same individuals are essential 

 if we are to make progress. A wide range of tests is called for 

 to cover the primary mental abilities as fully as possible: 

 and longitudinal studies are needed to allow for the very wide 

 individual differences in optimal performance level and in 

 performance decrement as age advances — individual differ- 

 ences which are submerged and undetectable when the mean 

 scores of large groups of people of different ages are compared. 

 This last difficulty is a most serious one. The great success 

 of the familiar methods of assessing level of intelligence in 

 children of different ages has caused us to concentrate more 

 on performance relative to others of the same age than on 

 rate and kind of change in the individual. So long as we are 

 ignorant of the performance level of an individual in his 



