A paper in the journal Neurology:
“Objective: To examine the relation of performance on brief cognitive tests to development of clinically diagnosed Alzheimer disease (AD) dementia over the following 18 years in a sample of African Americans and European Americans.
Methods: A composite cognitive test score based on tests of episodic memory, executive function, and global cognition was constructed in a prospective population-based sample of 2,125 participants (55% African American and 61% female) aged 65 years and older residing in 4 Chicago neighborhoods. Time before AD dementia diagnosis was categorized into 6 groups corresponding to data collection periods: 0.1–0.9, 1.0–3.9, 4.0–6.9, 7.0–9.9, 10.0–12.9, and 13.0–17.9 years.
Results: Of 2,125 participants without clinical AD dementia, 442 (21%) developed clinical AD dementia over 18 years of follow-up. Lower composite cognitive test scores were associated with the development of AD dementia over the duration of the study. The magnitude of association between composite cognitive test score and development of AD dementia increased from an odds ratio of 3.39 (95% confidence interval 1.72, 6.67; p < 0.001) at 13.0–17.9 years to 9.84 (95% confidence interval 7.41, 13.06; p < 0.001) at 0.1–0.9 years, per SD increment. These associations were consistently larger among European Americans than among African Americans. Performance on individual cognitive tests of episodic memory, executive function, and global cognition also significantly predicted the development of AD dementia, with associations exhibiting a similar trend over 18 years.
Conclusions: Our findings suggest that cognitive impairment may manifest in the preclinical phase of AD dementia substantially earlier than previously established.”
Here is the press release. The article is behind a paywall, so I cannot tell you which tests were used.
peakmemory 
I see “frequentist” methods were used, and the study is hidden behind a paywall … I wonder if the data in this study is available for others to review or replicate this study?
It is consistent with some other longitudinal studies, particularly Ian Deary’s research. For a good summary see his very readable book “Intelligence: A Very Short Introduction.”