Hi Annie - thank you for the great overview. What a blessing that the study cohort came from the Framington Heart Study. I have been using a fitness tracker for several years and now use a Garmin. I think it pretty accurately tracks sleep stages. I've found that two things will influence the amount of deep sleep I get - and if I lack them I can have very little deep sleep. 1) adequate exercise/workouts; 2) medical cannabis - only a small amt needed.