University of Michigan Health and Retirement Study (HRS)According to the website, the University of Michigan Health and Retirement Study (HRS) is a longitudinal panel study that surveys a representative sample of more than 26,000 Americans over the age of 50 every two years. Beginning in 1992, the study has collected information regarding income, work, assets, pension plans, health insurance, disability, physical health and functioning, cognitive functioning, and health care expenditures.