Does IQ Vary Systematically with All Measures of Socioeconomic Status in a Cohort of Middle-Aged, and Older, Men?

Shona J. Kelly, Nicholas R. Burns, Greta Bradman, Gary Wittert, Mark Daniel

Freemason’s Foundation Centre for Men’s Health and the Discipline of Medicine, University of Adelaide, Adelaide, Australia.
Sansom Institute for Health Research, University of South Australia, Adelaide, Australia; Department of Medicine, St. Vincent’s Hospital, The University of Melbourne, Parkville, Australia.
Sansom Institute for Health Research, University of South Australia, Adelaide, Australia; Freemason’s Foundation Centre for Men’s Health and the Discipline of Medicine, University of Adelaide, Adelaide, Australia.
School of Psychology, University of Adelaide, Adelaide, Australia.

DOI: 10.4236/sm.2012.24052                

Abstract

Differences in IQ have been offered as an explanation for socioeconomic gradients in morbidity and mortality. Previous research has largely relied on linking education and conscription testing data with later life health. As this early life testing was used to determine a person’s academic path it is difficult to disentangle the effects of IQ from education. This study used IQ and socioeconomic status (SES) data collected concurrently in mid-life from men who did not experience IQ-test-driven career path direction in early life. If IQ is associated with SES generally then multiple domains of IQ it will be associated with all components of SES. In a subsample of men aged 35 - 80 (n = 287) from the Florey Adelaide Male Ageing Study, we evaluated relationships between each of four domains of cognitive ability (IQ domains): fluid (Gf); crystallised (Gc); visual/spatial (Gv) and processing speed (Gs). SES was measured as standardized education, income, occupational prestige and deprivation score. Age-adjusted linear regression was used to test each SES-z-score individually against each IQ domain. Then all four SES measures were included in a single model for each IQ domain. This study found that a panel of standard IQ tests were positively associated with attained education but not with income or area-level deprivation score. Two IQ abilities, Gf and Gc, were also associated with occupational prestige score. These associations suggest that lesser levels of health associated with lower socioeconomic status is not accounted for by a lesser innate ability and that intervention may be possible.

Keywords

Intelligence; Social Class; Health Inequalities; Socioeconomic Status

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Australian Bureau of Statistics (2003). Census of population and housing. Belconnen, ACT: Central Office, Australian Bureau of Statistics.
[2]	Batty, G. D., & Deary, I. J. (2005). Education and mortality: A role for intelligence? Journal of Epidemiology & Community Health, 59, 809-810.
[3]	Batty, G. D., Deary, I. J., & Gottfredson, L. S. (2007). Premorbid (early life) IQ and later mortality risk: A systematic review. Annals of Epidemiology, 17, 278-288. doi:10.1016/j.annepidem.2006.07.010
[4]	Batty, G. D., Deary, I. J., Tengstrom, A., & Rasmussen, F. (2008). IQ in early adulthood and later risk of death by homicide: Cohort study of 1 million men. British Journal of Psychiatry, 193, 461-465. doi:10.1192/bjp.bp.107.037424
[5]	Batty, G. D., Der, G., Macintyre, S., & Deary, I. J. (2006). Does IQ explain socioeconomic inequalities in health? Evidence from a population based cohort study in the west of Scotland. British Medical Journal, 332, 580-584. doi:10.1136/bmj.38723.660637.AE
[6]	Batty, G. D., Gale, C. R., Tynelius, P., Deary, I. J., & Rasmussen, F. (2009). IQ in early adulthood, socioeconomic position, and unintentional injury mortality by middle age: A cohort study of more than 1 million Swedish men. American Journal of Epidemiology, 169, 606-615. doi:10.1093/aje/kwn381
[7]	Batty, G. D., Shipley, M. J., Mortensen, L. H., Boyle, S. H., Barefoot, J., Gronbaek, M. et al. (2008). IQ in late adolescence/early adulthood, risk factors in middle age and later all-cause mortality in men: The Vietnam experience study. Journal of Epidemiology & Community Health, 62, 522-531. doi:10.1136/jech.2007.064881
[8]	Blundell, R., Dearden, L., Meghir, C., & Sianesi, B. (1999). Human capital investment: The returns from education and training to the individual, the firm and the economy. Fiscal Studies, 20, 1-23. doi:10.1111/j.1475-5890.1999.tb00001.x
[9]	Calvin, C. M., Deary, I. J., Fenton, C., Roberts, B. A., Der, G., Leckenby, N., & Batty, G. D. (2011). Intelligence in youth and all-causemortality: A systematic review with meta-analysis. International Journal of Epidemiology, 40, 626-644. doi:10.1093/ije/dyq190
[10]	Chandola, T., Deary, I. J., Blane, D., & Batty, G. D. (2006). Childhood IQ in relation to obesity and weight gain in adult life: The national child development (1958) study. International Journal of Obesity, 30, 1422-1432. doi:10.1038/sj.ijo.0803279
[11]	Deary, I. J., Allerhand, M., & Der, G. (2009). Smarter in middle age, a cross-lagged panel analysis of reaction time and cognitive ability over 13 years in the west of Scotland twenty-07 study. Psychology and Aging, 24, 40-47. doi:10.1037/a0014442
[12]	Deary, I. J., & Batty, G. D. (2007). Cognitive epidemiology. Journal of Epidemiology & Community Health, 61, 378-384. doi:10.1136/jech.2005.039206
[13]	Deary, I. J., Batty, G. D., Pattie, A., & Gale, C. R. (2008). More intelligent, more dependable children live longer. A 55-year longitudinal study of a representative sample of the Scottish nation. Psychological Science, 19, 874-890. doi:10.1111/j.1467-9280.2008.02171.x
[14]	Deary, I. J., Whiteman, M. C., Starr, J. M., Whalley, L. J., & Fox, H. C. (2004). The impact of childhood intelligence on later life: Following up the scottish mental surveys of 1932 and 1947. Journal of Personality & Social Psychology, 86, 130-147. doi:10.1037/0022-3514.86.1.130
[15]	Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101, 171-191. doi:10.1037//0033-2909.101.2.171
[16]	Ginty, A. T., Phillips, A. C., Der, G., Deary, I. J., & Carroll, D. (2011). Cognitive ability and simple reaction time predict cardiac reactivity in the west of Scotland twenty-07 study. Psychophysiology, 48, 1022-1027. doi:10.1111/j.1469-8986.2010.01164.x
[17]	Hakstian, A. R., & Cattell, R. B. (1975). The comprehensive ability battery. Champaign, IL: Institute for Personality and Ability Testing.
[18]	Hart, C. L., Taylor, M. D., Davey Smith, G., Walley, L. J., Starr, J. M., Hole, D. J., & Deary, I. J. (2003). Childhood IQ, social class, deprivation, and their relationships with mortality and morbidity risk in later life: Prospective observational study linking the Scottish mental survey of 1932 and the midspan studies. Psychosomatic Medicine, 65, 877-883. doi:10.1097/01.PSY.0000088584.82822.86
[19]	Hart, C. L., Taylor, M. D., Smith, G. D., Whalley, L. J., Starr, J. M., Hole, D. J., & Deary, I. J. (2005). Childhood IQ and all-cause mortality before and after age 65: Prospective observational study linking the Scottish mental survey 1932 and the midspan studies. British Journal of Health Psychology, 10, 153-165. doi:10.1348/135910704X14591
[20]	Hemmingsson, T., Essen, J. v., Melin, B., Allebeck, P., & Lundberg, I. (2007). The association between cognitive ability measured at ages 18-20 and coronary heart disease in middle age among men: A prospective study using the Swedish 1969 conscription cohort. Social Science & Medicine, 65, 1410-1419. doi:10.1016/j.socscimed.2007.05.006
[21]	Holden, C. A., McLachlan, R. I., Pitts, M., Cumming, R., Wittert, G., Agius, P. A., & de Kretser, D. M. (2005). Men in Australia telephone survey (MATeS): A national survey of the reproductive health and concerns of middle-aged and older Australian men. Lancet, 366, 218-224. doi:10.1016/S0140-6736(05)66911-5
[22]	Lager, A., Bremberg, S., &Vagero, D. (2009). The association of early iq and education with mortality: 65 Year longitudinal study in Malmo, Sweden. British Medical Journal, 339, B5282. doi:10.1136/bmj.b5282
[23]	Lawlor, D. A., Batty, G. D., Clark, H., McIntyre, S., & Leon, D. A. (2008). Association of childhood intelligence with risk of coronary heart disease and stroke: Findings from the Aberdeen children of the 1950s cohort study. European Journal of Epidemiology, 23, 695-706. doi:10.1007/s10654-008-9281-z
[24]	Lawlor, D. A., Najman, J. M., Batty, G. D., O’Callaghan, M. J., Williams, G. M., & Bor, W. (2006). Early life predictors of childhood intelligence: Findings from the mater-university study of pregnancy and its outcomes. Paediatric and Perinatal Epidemiology, 20, 148-162.
[25]	Lee, S., Kawachi, I., & Grodstein, F. (2004). Does caregiving stress affect cognitive function in older women? Journal of Nervous and Mental Disease, 192, 51-57. doi:10.1097/01.nmd.0000106000.02232.30
[26]	Liberatos, P., Link, B. G., & Kelsey, J. L. (1988). The measurement of social class in epidemiology. Epidemiologic Reviews, 10, 87-121.
[27]	Marmot, M. (2004). Status syndrome: How your social standing directly affects your health and life expectancy. London: Bloomsbury.
[28]	Martin, S., Haren, M., Taylor, A., Middleton, S., Wittert, G., & FAMAS. (2007). Cohort profile: The florey adelaide male ageing study (FAMAS). International Journal of Epidemiology, 36, 302-306. doi:10.1093/ije/dyl279
[29]	McEwen, B. S., & Gianaros, P. J. (2010). Central role of the brain in stress and adaptation: Links to socioeconomic status, health and disease. Annals of the New York Academy of Sciences, 1186, 190-222. doi:10.1111/j.1749-6632.2009.05331.x
[30]	Muthén, L. K., & Muthén, B. O. (2010). MplusUser’s guide (6th ed.). Los Angeles, CA: Muthén & Muthén.
[31]	Neisser, U., Boodoo, G., Bouchard Jr., T. J., Boykin, A. W., Brody, N., Ceci, S. J., & Urbina, S. (1996). Intelligence: Knowns and unknowns. American Psychologist, 51, 77-101. doi:10.1037//0003-066X.51.2.77
[32]	Orpana, H. M., Lemyre, L., & Kelly, S. J. (2007). Do stressors explain the association between income and changes in self-rated health? A Longitudinal analysis of the national population health survey. International Journal of Behavioral Medicine, 14, 40-47. doi:10.1007/BF02999226
[33]	Pearce, M. S., Deary, I. J., Young, A. H., & Parker, L. (2006). Childhood IQ and deaths up to middle age: The Newcastle thousand families study. Public Health, 120, 1020-1026. doi:10.1016/j.puhe.2006.06.015
[34]	Queensland University of Technology, & Australian Institute of Health and Welfare (2004). Health inequalities in Australia: Mortality health inequalities monitoring series. Canberra: AIHW.
[35]	Raven, J., Raven, J. C., & Court, J. H. (1998). Manual for Raven’s progressive matrices and vocabulary scales. Sections 1 - 7 with 3 research supplements. San Antonio, TX: Harcourt Assessment/Pearson Assessment.
[36]	Salthouse, T. A. (2004). What and when of cognitive aging. Current Directions in Psychological Science, 13, 140-144. doi:10.1111/j.0963-7214.2004.00293.x
[37]	Schrank, F. (2005). Woodcock-Johnson III tests of cognitive abilities. In D. P. Flanagan, & P. L. Harrison (Eds.), Contemporary intellectual assessment: Theories, tests, and issues (2nd ed., pp. 371-401). NY: Guilford Press.
[38]	Treiman, D. J. (1977). Occupational prestige in comparative perspective. New York: Academic Press.
[39]	Undheim, J. O., &Gustafgsson, J. E. (1987). The hierarchical organization of cognitive abilities: Restoring general intelligence through the use of linear structural relations (LISREL). Multivariate Behavioral Research, 22, 149-171. doi:10.1207/s15327906mbr2202_2
[40]	Vandenberg, S. G., & Kuse, A. R. (1978). Mental rotations: A group test of three-dimensional spatial visualisation. Perceptual and Motor Skills, 47, 599-604. doi:10.2466/pms.1978.47.2.599
[41]	Wechsler, D. (1981). Wechsler adult intelligence test-revised. San Antonio, TX: Psychological Corporation.