Table 3 Description of sleep duration at age 50, 60, and 70 by groups of trajectories of sleep duration.

From: Association of sleep duration in middle and old age with incidence of dementia

  N Sleep duration, mean (standard deviation) (h)
Age 50 Age 60 Age 70
Persistent short 1358 6.0 (0.0) 6.0 (0.0) 6.0 (0.0)
Persistent normal 2520 7.2 (0.4) 7.0 (0.5) 6.8 (0.5)
Persistent long 461 8.0 (0.0) 8.0 (0.0) 7.8 (0.4)
Change from short to normal 1086 6.0 (0.0) 6.7 (0.6) 6.9 (0.6)
Change from normal to long 946 6.9 (0.5) 7.5 (0.6) 8.0 (0.0)
Change from normal to short 504 7.1 (0.3) 6.0 (0.1) 6.0 (0.0)