Intelligence and Emotion in Ageing 179 



between mental test ability at different ages emphasizes the 

 concepts of ambiguity of content and of process in the estima- 

 tion of intellectual ability at different ages. Intelligent 

 behaviour, however, may only be apparently inconsistent at 

 successive ages to the degree that the variety of educational 

 opportunities, of environmental stimulations, or of physio- 

 logical changes in physical fitness, visual acuity, speed of 

 reaction, or metabolism affect the scores. 



The opportunities involved in formal education influence 

 the test results of adults in a large variety of intellectual 

 items. When it is recognized that "highest grade reached" 

 is an undifferentiated mixture of quantity and quality, 

 the conclusion is somewhat strengthened. Highest grade 

 reached credits each year of formal instruction — academic, 

 vocational, or leisure time — regardless of the quality of the 

 instruction. It is significant historically that the Committee 

 on the Psychological Examination of Recruits in 1917 ( Yerkes, 

 1921) set among their criteria for a group test of intelligence, 

 non-dependence upon schooling, but that the empirical results 

 between the group test (predecessor to Army Alpha) and 

 reported length of schooling was significantly correlated. 



Many of the studies of cross-sections of the population, 

 therefore, must consider the influence of differential schooling 

 in relation to variations among age groups. If the older in- 

 dividuals have had less schooling, i.e. if the amount of school- 

 ing is negatively related to age, some of the reported relations 

 of intelligence with age may be reflecting differences in educa- 

 tional opportunity. Despite this limitation, it is significant 

 that mental ability, appraised by means of vocabulary tests, 

 seems to be well maintained throughout life. 



The relatively greater decline in performance tests as com- 

 pared with vocabulary has been responsible for the invention 

 of the notion of intellectual deterioration. Babcock (1930), 

 utilizing the hypothesis based on one of Jost's laws that "the 

 oldest learning is last to be lost" developed a test whereby 

 intellectual level is estimated from vocabulary and compared 

 the performances on other tests with this level. It must be 



