Intelligence and Emotion in Ageing 173 



researches on the social and intellectual data of senescent 

 twin pairs (Kallmann, Ferngold and Bondy, 1951), most 

 longitudinal studies have been concerned with the evaluation 

 of growth and development in the period from early infancy 

 to early maturity. The primary inadequacy of follow-up 

 studies has been its relative inflexibility to capitalize on the 

 development of new techniques for the measurement of traits 

 or processes. Were a new method discovered for assessing 

 emotion or intelligence or blood chemistry, the researcher 

 would not be able to obtain retrospective measures of the 

 trait. Occasionally, the need for repetitive measurements in 

 the same sample at different times is eliminated because the 

 generalization was established by the cross-sectional method. 



Obviously, the two methods are complementary. In the 

 ageing process, it is recommended that both methods be used 

 simultaneously to capitalize on the advantages of each. The 

 proposed method is tentatively named as the combined over- 

 lapping method. Essentially, the method would involve the 

 selection of representative samples of individuals at specified 

 ages (as in the cross-sectional method) and to follow each of 

 these samples for a number of years (as in the longitudinal 

 method). There then would be a number of cohorts, each of 

 which would provide data at any time of age-differences 

 between cohorts, and, after a period of study, an appraisal of 

 age changes within each cohort, as well. Moreover, the relative 

 consistency of the results for different cohorts, reaching the 

 same age, would supply evidence of the effects of selective 

 elimination by death or accident. The introduction of newer 

 techniques, furthermore, would be facilitated, since the tech- 

 nique could be applied to any cohort over its shorter run of 

 years. The combined overlapping method thus could provide 

 evidence about age differences and about age changes. 



Any method may be made more valuable by the utilization 

 of retrospective data, e.g. as Kallmann has done so successfully 

 in the senescent twin study (cf. Goldfarb, 1955). Retrospec- 

 tive data, whether supplied by the individual under study or 

 supplied by others (parents, teachers, physicians, etc.) can 



