PROVO — The long-accepted belief that teens need lots of sleep to be at their best may not be accurate, according to research from BYU just published in the Eastern Economic Journal.

While federal guidelines say teens need nine hours of shut-eye a night, the Brigham Young University researchers found that teens 16-18 do their best work on standardized tests when they get seven hours of sleep.

"It's a different approach empirically than studies by medical researchers," said Mark Showalter, BYU economics professor and co-author of the study with colleague Eric Eide. "It was designed to see optimum sleep associated with test scores ... If it was always better with more sleep, it would have shown that."

Because national numbers have long said youths need around 9.25 hours sleep a night, the researchers were surprised by the shorter sleep number they found. But when they tried to determine where the original 9.25 hours came from, they were nearly stymied, he said.

"The best we can determine, studies in the 1970s over a period of years took students into a sleep lab to see how much sleep they gravitated toward. It was nine hours." What those studies showed, he said, is how much sleep they'd like to get, not how much sleep teens actually need to do their best academically.

Nine hours is "fine, but it's not realistic. Maybe, if you have nothing else to do with your time, it's reasonable. But if you want time to study, to do other things, it's not at all clear that's the best use of time.

"Nine hours it not something the top-scoring kids on anything were doing on a regular basis."

As for more or less, a little time — say an hour either direction — didn't make much difference. Their findings formed an inverted U shape. The further away from optimal sleep time one gets, the more dramatic the difference in performance. A teen sleeping fewer than five hours or more than 10 on a regular basis saw substantial declines in the standardized test scores.

As for the federal guideline based on how much sleep teens gravitate to, Showalter likened it to deciding how much a person should eat by putting them in a well-stocked pantry to see what they did eat. "Somehow, that doesn't seem right."

The study included 1,724 students ages 10-18 from across the country who were given four basic test like simple reading comprehension and basic math skills. It showed that 10-year olds need 9-9.5 hours, while 12-year olds need an hour less. At 16, the need has dropped to seven hours. The effect of optimal sleep duration on the test scores varied, but a "90-minute shift toward the optimum is comparable to the child's parents completing about one more year of schooling," a release accompanying the study said.

EMAIL:, Twitter: Loisco