Some struggle with medical issues - like insomnia - that make sleep hard. But for many of us, the quantity and quality of sleep come down to a matter of choice. Still, only a few enterprising economists have looked closely at this, and generally, those have assumed that we choose our hours of sleep optimally.

Web searching and cellphone use both flourish in the wee hours. Before the dawn of the web, I would stay up watching television. But there is something soporific about television: I would often nod off. Not so when I'm online. As technologies expand, these problems may only worsen.

Eat better or work out more, and you'll see the benefits weeks, months or years down the road. Sleep more, and you'll see the benefits tomorrow.

Sendhil Mullainathan Quotes