If you're having trouble sleeping, finding out what the problem is can be hard. Sleep trackers can help. To really get a fix on what's keeping you tired, focus on your sleep efficiency number (and, specifically, how it changes).
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As news site the Vox explains, your sleep efficiency number is how much time you spend actually sleeping, versus simply being in bed rolling around. Sleep trackers like Fitbit or even smartphone apps can help you measure this. Don't worry about what the ideal is though, because there isn't one. The important detail is whether it changes:
Rachel Salas, a neurologist who focuses on sleep at Johns Hopkins, puts it this way, "I wouldn't necessarily seek help if you're looking at sleep efficiency based on a device and see no other signs [of a problem]." Those signs could be things like excessive, unexplained sleepiness during the day or trouble falling or staying asleep at night.
So why even measure sleep efficiency? In part, because people could find it helpful to track sleep efficiency over time -- and see how it differs in response to changes in their own lives: "The value of that number is in whether it changes," says Michael Twery, director of the National Center on Sleep Disorders Research at the National Institutes of Health. (And also, who wants to waste time in bed not sleeping?)
This can help you identify habits you have during the waking hours that can result in lost sleep. If you find that you're sleeping less after screen reading for example (spoiler: you are), you know to cut that out.