What is "sleep efficiency?"

My sleep study notes a "sleep efficiency" of 87.5% - with norms of 85-99.
What does this mean? I certainly don't feel that I sleep efficiently!!

Percent of time asleep compared to time in bed, I believe. So in other words, you don't lie awake at night for hours before falling asleep, or wake up in the middle of the night unable to fall back to sleep, etc.

Sleep efficiency is part of proper "sleep hygiene." It's the amount of time you spent asleep in minutes divided by the amount of time you were in bed (multiplied by 100 to convert the decimal into a percentage). I've heard from more than one source that over 80% is normal.

Every morning I write down those numbers and calculate them. I keep mine at 85-90%, with or without the CPAP. Now granted, this is far from exact, since I base it purely on what I'm remembering. It's still a good estimation, though. The way to increase effiiciency is:

• If at all possible go to bed and set your alarm for the same time every day.
  
  Look at your stats and set your alarm for the amount of time you're typically asleep during the night. (Guess if you have to!) Then once your efficiency is over 85%, if you need to increase the amount of time you're in bed by fifteen minutes every couple of days, as long as your efficiency stays up.

FWIW, to track my sleep hygiene, I write down the following each morning in a grid. I do it because it tracks what's important to me that can affect my sleep patterns. You may want to customize it for yourself:
Sleep aids
1. How long did you you nap yesterday?
2. Did you take medications for sleep last night?
3. Did you use the CPAP machine (yes/no and all night/partly)
Planning
4. What was your planned bed time?
5. What was your planned wake-up time?
Actuals
6. What time did you turn off the lights to go to sleep?
7. How long did it take you to fall asleep? (in minutes)
8. How much time were you awake during the night? (in minutes)
9. What was your final awakening?
10. What time did you get out of bed?
11. How much time elapsed from the time you turned off the lights to time you got out of bed in minutes? (6 to 10)
12. How much sleep did you get in minutes? (6 to 9) - (7+8)
13. Compute your sleep efficiency (12/11)
14. Did you do hypnosis?
15. Rate how sleepy you felt yesterday? (1=not at all, 10=extremely sleepy)
16. Comments (exercise, "midnight" snacks, caffeine, time of day of naps, etc.):

Doug.