Olga Khazan explains:

Though Americans across the economic spectrum are sleeping less these days, people in the lowest income quintile, and people who never finished high school, are far more likely to get less than seven hours of shut-eye per night. About half of people in households making less than $30,000 sleep six or fewer hours per night, while only a third of those making $75,000 or more do.

Unsurprisingly, shift workers face the greatest risk of sleep deprivation; they get two to four hours less sleep than average. The consequences can be dire:

Exposure to bright light when it’s time to sleep makes it harder for the body to produce melatonin, a sleep hormone. Over time, this sleep deprivation translates to an increased risk for heart disease, gastrointestinal problems, and reproductive issues. … For some, a sleep shortfall can lead to narcolepsy-like symptoms. One study found that 53 percent of night-shift workers report falling asleep accidentally on the job.