Rates of senile dementia, Alzheimer's type, in the Baltimore Longitudinal Study

Research participants (519) in the ongoing Baltimore Longitudinal Study, Gerontology Research Center, National Institute on Aging, from 1958-1978 were screened for new onset of Senile Dementia-Alzheimer's Type (SDAT), a global and progressive cognitive disorder. Their medical record abstracts were reviewed by two psychiatrists, who applied algorithmic criteria to identify 27 incident cases and date onsets. Intrarater bias, interrater reliability, and concurrent validity of the case ascertainment methods were assessed. A radix was created to estimate age-specific incidence rates, prevalence rates, remaining lifetime morbid risk for the disease-free and expected years of impairment with disease. Incidence was modeled as an exponential function of chronological age beyond 60. Survival analysis failed to detect premature death among SDAT cases; death rates depended only on chronological age--not on disease acquisition, duration, or age at onset. Prevalence at every age depended on incidence, exceeding 50% among those 95 and over.