The UDS study population
NACC’s Uniform Data Set (UDS) is valuable resource for the AD research community because of the sample size, power, and comparability it offers. However, because of the way subjects are recruited, it is not suitable for research questions that require a statistically based sample of the U.S. population. Following are characteristics of the UDS study population that investigators should keep in mind when formulating their research questions:
- The UDS reflects the total enrollment at the ADCs since 2005 and includes subjects with a range of cognitive status — normal cognition, MCI, and demented.
- Each Center enrolls its subjects according to its own protocol. Subjects may come from clinician referral, self-referral by patients or family members, active recruitment through community organizations, and volunteers who wish to contribute to research on various types of dementia. Most Centers also enroll volunteers with normal cognition, and these tend to be highly educated.
- NACC subjects with dementia are not a statistically based sample of the U.S. population with or without dementia. Rather, they are best regarded as a referral-based or volunteer case series. Therefore, NACC data do not lend themselves to estimates of the prevalence or incidence of dementia subtypes in the general U.S. population.
- Some ADCs require that participants agree to autopsy 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
- The UDS data are collected via a standardized evaluation of subjects enrolled in ADCs; data are recorded directly on UDS forms (hard copy or electronic) during the evaluation process.
- The UDS is longitudinal, and its protocol requires approximately annual follow-up as long as the subject is able to participate. Late-stage subjects who become unable to participate may be followed for autopsy only after they discontinue their UDS follow-up visits. For more information, please see UDS Data Collection Protocol.
- Data are collected by trained clinicians and clinic personnel from subjects and their co-participants (usually a close friend or family member).
- Diagnosis is made by either a consensus team or a single physician (the one who conducted the examination); this process varies according to each ADC's protocol.
- Although the focus of the ADCs is Alzheimer's disease, the Centers also collect data on a variety of associated disorders, such as vascular dementia, Lewy body dementia, and frontotemporal lobar degeneration.
- Information is collected during in-person office visits, home visits, and telephone calls. In addition, Milestone Forms are used to document subject death and drop-out.