Why you're probably getting more sleep than you think

If you ask anyone how much sleep they typically get, you'll more than likely hear a relatively low number - something like, "four or five hours."

But that number may not be an honest representation of how many hours they actually snooze each night, writes Laura Vanderkam in her new book "I Know How She Does It."

"If you talk to any group of busy people, they will tell you in great detail how little sleep they think they are getting, on some nights at least, and they will mean it," she writes.

Many sleep studies that ask these kinds of questions, however, may produce an inaccurate account of people's sleep habits for three important reasons.

1. Sleep surveys ask about sleep.

"People are primed to think about sleep as they answer the questions, and since negative experiences stand out in the mind more than good ones, the tendency is to call the bad nights to mind first," Vanderkam explains.

Survey respondents are also more likely to give answers that reflect the common narrative that our consistent lack of sleep is a badge of honor when they're primed to think about sleep, she says.

"Getting adequate sleep is a sign that the world doesn't need your attention for seven to nine hours each day," she writes. "It keeps spinning as usual in its orbit. Who wants to admit that?"

2. Surveys sometimes ask how much people sleep "per night."

This means that people are less likely to mention unplanned, non-nightly sleep.

More reputable surveys like those from The National Sleep Foundation do ask about naps and find that they happen with some regularity - and numerous studies indicate that naps can relieve sleep deprivation and boost productivity. But naps often don't register as real sleep to people, especially when the norm is to only consider nightly snoozes.

3. Surveys often ask people how much sleep they get on a "typical" night.

The biggest problem, Vanderkam says, is the idea that there is such a thing as a "typical" night. "The truth is that for many people, typical nights don't exist," she writes.

Sleep deprivation is viewed as a sign of importance these days, Vanderkam says, and so we're often tempted to view the shortest nights as the norm, while we ignore the much longer nights of sleep we get. Weekends, for example, make up 29% of our days, even though we rarely view them as "typical."

"In a world where we complain about how busy we are, we're not going to mention that five out of seven nights per week we sleep just fine," she writes. "It's the nights that a kid woke up at 2 a.m. and you had to catch a seven a.m. flight that you talk about at parties or mention in your departure memo.

"It's not that the horrible night didn't happen. It's just that it's no more emblematic of life than any other night. It must be taken in context."

In researching her book, Vanderkam studied the weekly time logs of 142 women who make at least $100,000 a year. In analyzing these women's sleep habits, she immediately saw that sleep times varied widely throughout the week, making it impossible to identify a "typical night."

The best way to get an accurate view of your sleeping habits, Vanderkam says, is to keep your own weekly time log. "Record all your sleep, even if it didn't happen at 'typical' times, and whether it fits with your mental picture or not."