To what extent does IQ 'explain' socio-economic variations in function?
BACKGROUND
The aims of this study were to examine the extent to which higher intellectual abilities protect higher socio-economic groups from functional decline and to examine whether the contribution of intellectual abilities is independent of childhood deprivation and low birth weight and other socio-economic and developmental factors in early life.


METHODS
The Maastricht Aging Study (MAAS) is a prospective cohort study based upon participants in a registration network of general practices in The Netherlands. Information was available on 1211 men and women, 24-81 years old, who were without cognitive impairment at baseline (1993-1995), who ever had a paid job, and who participated in the six-year follow-up. Main outcomes were longitudinal decline in important components of quality of life and successful aging, i.e., self-reported physical, affective, and cognitive functioning.


RESULTS
Persons with a low occupational level at baseline showed more functional decline than persons with a high occupational level. Socio-economic and developmental factors from early life hardly contributed to the adult socio-economic differences in functional decline. Intellectual abilities, however, took into account more than one third of the association between adult socio-economic status and functional decline. The contribution of the intellectual abilities was independent of the early life factors.


CONCLUSIONS
Rather than developmental and socio-economic characteristics of early life, the findings substantiate the importance of intellectual abilities for functional decline and their contribution--as potential, but neglected confounders--to socio-economic differences in functioning, successful aging, and quality of life. The higher intellectual abilities in the higher socio-economic status groups may also underlie the higher prevalences of mastery, self-efficacy and efficient coping styles in these groups.
Bosma
Hans
H
Maastricht University, Social Medicine, Maastricht, The Netherlands. hans.bosma@zw.unimaas.nl
van Boxtel
Martin P J
MP
Kempen
Gertrudis I J M
GI
van Eijk
Jacques Th M
JT
Jolles
Jelle
J
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology / Q000523:psychology; D003072:Cognition Disorders / Q000191:economics / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007361:Intelligence Tests / Q000706:statistics & numerical data*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D009790:Occupations / Q000145:classification / Q000191:economics*; D011446:Prospective Studies; D011788:Quality of Life / Q000523:psychology*; D012923:Social Class; D012959:Socioeconomic Factors; D012962:Sociology, Medical