While the majority of previous studies of centenarians have used convenience samples, Phase III of the GCS provides normative data on a population-based sample of centenarians. As a result, we expect these results to be more applicable for comparison in applied settings such as assisted living, skilled nursing homes, and physician and clinic offices. Three well-validated measures of cognitive performance – MMSE, SIB, and BDS – provide a significant expansion of the kinds of cognitive abilities we are able to measure in the oldest old. Not surprisingly, our results suggest that centenarians in fact look very different on cognitive testing than do even the oldest age ranges of most normative aging datasets (e.g., 80–90). However, results support the use of both global (e.g., MMSE, SIB) and domain-specific (e.g., BDS) measures of neurocognition to describe cognitive abilities in this oldest old cohort, and these normative tables should provide a significantly improved set of comparison scores in which to do so. For convenience, we have provided both age cohort means and standard deviations () as well as centile scores within specific age cohorts ( and ).
Several aspects of our study should be noted. Importantly, as this was a population-based study, no filtering for dementia was conducted. Earlier studies of centenarians have reported considerable dementia in their samples, ranging from 42 to 100% (see Gondo & Poon, 2007
, for a review). As can be seen in our population, the average centenarian shows significant cognitive impairment as reflected in all of our primary measures, albeit as a group showing considerable variability. Further, cognitive performance across all measures drops significantly per each age cohort, underscoring the increased significance of small changes in age for these oldest old as well as the need to compare against more exact ages. This pattern is strikingly seen in –.
We also provided statistical population-adjusted weighted scores for all age and centile groups in addition to our actual scores. While these generally differed only slightly, and primarily at the high and low ends of the performance ranges, we felt they were important to include for aging researchers who might need a strict population estimate from which to compare.
A limitation of our tables is the lack of separation of our groups by residential status, i.e., community dwelling versus institutionalization. Unfortunately, our participant numbers were too small to provide stable scores for these subgroups. For preliminary consideration, we additionally provided cohorts divided by an educational dichotomy – less than high school and high school or better. The cohort `N's for these subgroups are obviously small at the extreme ends, and we want to acknowledge that these should thus be used cautiously. Another limitation of all centenarian studies is the potential impact of sensory deficit or motor impairment on performance. In our study, persons unable to complete an item of a task due to sensory or motor impairment were given a `0' for that item. Thus, this should be kept in mind for comparison. Still, we hope that as a group, these tables allow researchers and clinicians to gain a sense of where their oldest old patients/participants/clients stand compared to their peers and thus allow them to make reasoned judgment of relative cognitive ability.