Participants with (n = 259) and without MCI were recruited into parallel studies using comparable methods at 68 ADCS sites. Common entry criteria were aged 55 to 90, no use of antidementia drugs or other drugs known to affect cognition, and an available informant who lived with the participant or had personal encounter with the participant at least 6 to 8 hours more than 1 day per week and accompanied the participant to all clinic visits for the study period. Criteria specific to participants with MCI were memory complaints verified by an informant, abnormal memory function below an education-adjusted cutoff on the Logical Memory II subscale (Delayed Paragraph Recall) of the Wechsler Memory Scale,13 Mini-Mental State Examination (MMSE) score of 24 or less,14 Clinical Dementia Rating Scale (CDR) score of 0.5,15 and general cognition and functional performance sufficiently preserved such that the site physician could not make a diagnosis ofAD at screening. Criteria specific to controls required absence of depression or other neurodegenerative conditions; absence of a memory complaint; normal cognition as indicated by a CDR score of 0, a Global Deterioration Scale score of 1, or 2,16 or a MMSE score greater than 26; and a Hamilton Depression Rating Scale score less than 1.17
Twenty percent of controls were required to be nonwhite minorities. After baseline assessment, participants were followed annually for 3 years, with follow-up evaluations performed within a 2-week period of the scheduled followup date. Institutional review board approval was obtained at each participating ADCS site, and written informed consent was obtained from all study participants and informants.