Exclusive: What Fitbit’s 6 billion nights of sleep data reveals about us

How we sleep is unbelievably important. Getting too little sleep not only makes you feel lousy and cranky, but it’s also linked to obesity, diabetes, hypertension, and even early death. (No pressure.)

But it’s amazingly hard to measure our sleep, as a population. Sure, one person at a time can stay overnight at a sleep lab, hooked up to scalp electrodes — but try sleeping normally that way, away from home and wired to strange equipment. Other sleep studies use self-reporting, where you write down each morning how you slept, but that data is famously unreliable.