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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.

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.

We used the method of correlated vectors on 441 Korean older adults at risk for AD and 44 with AD.

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.

A composite neurocognitive score may show a clearer contrast between APOE carriers and noncarriers than a large number of …