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Keysor JJ, Jette AM.Keysor JJ, et al. Among authors: jette am.J Gerontol A Biol Sci Med Sci. 2001 Jul;56(7):M412-23. doi: 10.1093/gerona/56.7.m412.J Gerontol A Biol Sci Med Sci. 2001.PMID: 11445600Review.