The study population: The UDS

• Subjects with dementia, subjects with MCI, and cognitively intact subjects are included in the UDS and reflect the total enrollment at ADCs since 2005.

• Data are collected by trained clinicians from subjects as well as from their self-designated informants (usually a close friend or family member). Diagnoses are assigned either by a consensus team or a single physician who conducted the examination; this process varies according to each ADC's protocol.

• NACC subjects with dementia are not a statistically based sample of the U.S. population with or without dementia and are best regarded as a referral-based or volunteer case series. Therefore, NACC data do not lend themselves to estimates of the occurrence of dementia subtypes in the general U.S. population. Demented, MCI, and cognitively normal subjects are recruited in a variety of ways, in accordance with each ADC's custom protocol; in general, they tend to be highly educated volunteer research subjects.

• Many ADCs require that all participants agree to autopsy study before being accepted for UDS participation; this may impose further selection pressures on the makeup of the NACC sample.

• Written informed consent is obtained from all participants and informants.

Data collection for the UDS

• UDS data collection began in September 2005. The UDS data comprise a standardized evaluation of subjects enrolled in ADCs; data are recorded directly on UDS forms (hard copy or electronic) during the evaluation process. UDS protocol requires annual, longitudinal follow-up as long as the subject is able to participate; late-stage subjects who have previously been enrolled in the UDS may be followed for autopsy-only after discontinuing UDS visits.

• While the focus of the ADCs is Alzheimer's disease, the Centers also enroll and collect data on a variety of associated disorders, such as vascular dementia, dementia with Lewy bodies, and frontotemporal lobar degeneration.

• The UDS includes more than 700 variables, representing demographics, behavioral status, cognitive testing, medical history, family history, clinical impressions, and diagnoses. (APOE genotype is included in the NACC database for many subjects, but it is collected by request and is not an element of the UDS data collection forms.)

• Information is collected from in-person office visits and telephone calls, as well milestone forms documenting subject death and drop-out.

Summary statement

As of March 1, 2014, the UDS had accrued 29,913 subjects, representing over 85,556 subject visits and 33 unique ADCs. For a chart that provides an overview of the entire NACC database — including information on the Minimum Data Set and the Neuropath Data Set as well as the UDS — click here.