The LifeAfter90 study measured 4-metre walk speed in 502 ethnoracially diverse adults aged 90 and over (mean age 92.9) and followed them for an average of 3.6 years, during which 259 died. Each standard deviation (0.21 m/s) of faster gait speed carried a 20% lower mortality risk after adjustment for demographics. The association was confined to those aged 90-94 (HR 0.70, 95% CI 0.60-0.82); at 95 and over it was absent (HR 1.02, 95% CI 0.77-1.30), with no differences by sex, race/ethnicity or assistive device use.
Why it is interesting: A function measure that discriminates mortality risk well in the young-old loses its signal at the very ages where selection and measurement limits bite hardest.