The ACT study is a longitudinal population-based prospective cohort study of brain aging and incident dementia in the Seattle metropolitan area. ACT is a Repository administered by the Group Health Research Institute (GHRI), which has established policies and procedures for sharing data with external investigators. Data available from this project web site do not require any additional Institutional Review Board (IRB) approval or permissions. Linking those data with other ACT study or Group Health data would require additional review which can be initiated by contacting ACTproposals@ghc.org.