The authors have declared no competing interest. The Health and Retirement Study is supported by the National Institute on Aging (U01 AG009740). This analysis was supported by the National Institute on Aging (R01 AG055406, R01 AG067592, P30 AG072931, R01 AG075719, R01AG070953). I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.