Dementia and cognitive impairment in the oldest old: a comparison of two rating methods.

Rates of cognitive impairment in a representative population of the oldest old (aged 84 to 90) were examined using two indicators: The Global Deterioration Scale (GDS), and a Cognitive Rating (CR) derived from performance on five neuropsychological tests. Prevalence was estimated at 25.3%, using the GDS, and 30% with the CR. The overall degree of congruence between the measures was high, with most disagreements involving mildly impaired cases. The results indicate a high degree of convergence of clinical and neuropsychological indicators. The findings also confirm high rates of impairment among the oldest old.