The HRS is a nationally representative sample with oversamples of African-American and Hispanic populations. The target population for the original HRS cohort includes all adults in the contiguous United States born during the years 1931–1941 who reside in households. HRS was subsequently augmented with additional cohorts in 1993 and 1998 to represent the entire population 51 and older in 1998 (b. 1947 and earlier). Since then, the steady-state design calls for refreshment every six years with a new six-year birth cohort of 51–56 year olds. This was done in 2004 with the Early Baby Boomers (EBB) (b. 1948-53) and in 2010 with the Mid Boomers (MBB) (b. 1954–59).

This data release includes respondents who consented to the saliva collection in 2006 (‘Phase 1’), 2008 (‘Phase 2’), 2010 (‘Phase 3’), and 2012 (‘Phase 4’).  Thus, Phases 1 and 2 include samples from HRS panel respondents (largely b. < 1954)  while Phases 3 and 4 include samples from the MBB cohort, an additional minority oversample enrolled in HRS in 2010, and panel non-responders/consenters from 2006 and 2008.