Fig. 2.

Schematic depiction of the importance of both levels of and changes in cognitive performance for understanding functional independence and dementia in older age. People reach functional-impairment thresholds at different points in older age because they start out with different levels of cognitive performance (compare the solid lines), because they experience different rates of cognitive change (i.e., different within-persons development; compare the solid lines with the dashed lines), or because of a combination of those differences. Initial differences between people in levels of performance can affect the age at which cognitive declines significantly interfere with daily life and, in turn, the point at which dementia is diagnosed (compare the two dashed lines). Gf = fluid abilities.