The Stability of Intelligence From Age 11 to Age 90 Years

Deary, Ian J.; Pattie, Alison; Starr, John M. · 2013 · Crossref

DOI: 10.1177/0956797613486487

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Summary

This study investigates the long-term stability of individual differences in cognitive ability, specifically examining the correlation between intelligence scores obtained at age 11 and those obtained at age 90. The research addresses a critical gap in cognitive aging literature, as few studies have tracked the same individuals from youth into very old age. Understanding this stability is essential for estimating how much variance in late-life cognition is attributable to lifelong stable traits versus age-related changes, which informs theories of cognitive reserve and the protection against brain pathology. The authors utilized data from the Lothian Birth Cohort 1921, a longitudinal study of individuals born in Scotland in 1921. The analysis focused on 106 participants who had taken the Moray House Test No. 12 (MHT), a measure of general mental ability, during the 1932 Scottish Mental Survey at age 11 and again during the fourth wave of data collection at age 90. To assess concurrent validity, participants at age 90 also completed a battery of additional cognitive tests, including Raven’s Progressive Matrices, the National Adult Reading Test, the Mini-Mental State Examination, and various Wechsler memory and processing speed tests. Demographic, health, and genetic data were also recorded. The primary finding was a correlation of .54 (95% CI = .37 to .67) between MHT scores at age 11 and age 90. This indicates moderate stability in intelligence across nearly eight decades. While mean MHT scores at age 90 were slightly higher than at age 11, they were lower and more variable than scores recorded at ages 79 and 87. The MHT demonstrated strong concurrent validity at age 90, correlating significantly with all other cognitive tests administered. Principal components analysis revealed that childhood intelligence and crystallized measures (like the National Adult Reading Test) loaded on a distinct component from current fluid abilities, though the two components were correlated. Notably, correlations between childhood MHT scores and most adult cognitive tests were significantly lower than correlations between the age-90 MHT and those same tests, except for the National Adult Reading Test and Verbal Fluency. The study concludes that individual differences in general mental ability remain moderately stable from childhood to old age. This correlation provides a foundational estimate for future research into the causes of cognitive change across the life course. The authors note that the sample, while representative of survivors to age 90, had higher childhood intelligence than the general population, which may influence the estimates. Nevertheless, the findings offer valuable insights into the persistence of cognitive traits and the distinct contributions of prior versus current cognitive ability in very old age.

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• individual differences