Abstract
BACKGROUND: Being a carrier of the apolipoprotein E (APOE) ε4 allele is a clear risk factor for development of Alzheimer's disease (AD). On some neurocognitive tests, there are smaller differences between carriers and noncarriers, while other tests show larger differences. AIMS: We explore whether the size of the difference between carriers and noncarriers is a function of how well the tests measure general intelligence, so whether there are Jensen effects. METHODS: We used the method of correlated vectors on 441 Korean older adults at risk for AD and 44 with AD. RESULTS: Correlations between APOE carriership and test scores ranged from -.05 to .11 (normal), and -.23 to .54 (AD). The differences between carriers and noncarriers were Jensen effects: r = .31 and r = .54, respectively. CONCLUSION: A composite neurocognitive score may show a clearer contrast between APOE carriers and noncarriers than a large number of scores of single neurocognitive tests.