Major characteristics of the Betula study on memory, health, and aging (Nilsson et al., 1997, 2004) were presented. In addition, reliability and stability coefficient (5 and 10 years) were computed for individual measures of episodic memory and semantic memory (and for Block
Design and MMSE) and for unit-weighted composites (min. n = 1000, 830, and 643 for T1, T2, and T3, respectively). Reliability estimates ranged from .42 to .88 overall. Stability coefficients were substantial at the composite level (r = 77-.83) and did not differ for younger (35-55 years) and older adults (60-80 years). Finally, the stability coefficients decreased minimally over retest intervals, regardless of age. Together, the results indicate considerable stability of inter-individual differences of declarative memory across age and time, suggesting that the heterogenity of the aging processes, at least as reflected at the behavioral level, may be less prominent than is often asserted. This indication of relative lack of diversity needs to be supplemented with careful analyses of differences/changes in variance across age and time.
2006. Vol. 7, 6-14 p.