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The flowchart of the study design. (A) The study design and concept map. (B) The participants selection. HRS, the US Health and Retirement Study; ELSA, the English Longitudinal Study on Ageing; SHARE, the Survey of Health, Ageing and Retirement in Europe; CHARLS, the China Health and Retirement Longitudinal Study; KLoSA, the Korean Longitudinal Study of Aging.
