Project 4: HAALSI National—Abstract We propose to add a nationally representative cohort to the existing Agincourt sample of the Health and Aging in Africa: Longitudinal Study in South Africa (HAALSI) Program, allowing us to conduct the first nationally representative study of cognitive function and dementia in South Africa. Our broad array of health and socio-economic measures will be collected from a national cohort, making ours the first study from a Sub- Saharan African country to be included in the international family of Health and Retirement Studies (HRS) and allowing comparative research between HAALSI and HRS sister studies. We will conduct a national Harmonized Cognitive Assessment Protocol (HCAP) study to establish a reliable algorithm to give estimates of mild cognitive impairment (MCI) and dementia prevalence. We will measure the prevalence of cognitive impairment and dementia in South Africa and examine how it relates to socioeconomic status (SES). We will determine how the cognition-SES gradient varies for different measures of SES and investigate the underlying reasons for any differences. A goal of our study is to produce and quickly disseminate data for public use by researchers both in South Africa and internationally. A major advantage of our study will be our ability to expand the HAALSI Program’s breadth and depth, by combining the results of the national survey with the more detailed community results from the HAALSI Agincourt cohort and the detailed cognition studies embedded in that cohort. In Aim 1, we will recruit participants and collect the first wave of data for the HAALSI National cohort, a nationally representative longitudinal cohort of 4500 people 40 years of age and older (and their partners), to study healthy aging and cognition in South Africa. The detailed HCAP battery is administered to a subcohort which allows us to derive predictive algorithms for ascertainment of MCI and dementia in the full National cohort. In Aim 2, we will estimate the rate of cognitive impairment in our National cohort and investigate how cognitive ability varies by SES in South Africa. In Aim 3, we will study the generalizability of estimates of the determinants of cognitive decline, MCI, and dementia from the Agincourt community to the National level and pilot extending the survey to additional communities in the South African Population Research Infrastructure Network (SAPRIN). Impact: This project will extend the HAALSI Program to the national level in South Africa to produce insights that will inform policymaking and the development of interventions to support healthy aging.