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Stanford University School of Medicine

Sleep deprived suffer performance loss, according to new study

More bad news for insomniacs and those of us who struggle to get enough sleep at night. Lack of sleep definitely affects your performance the next day, and probably for a longer period of time than you might expect, according to a new study.

Among the findings: Two consecutive nights of less than six hours could leave you sluggish for the following six days. (Surprised? You aren't alone: This stat sparked a gasp of dismay at my office staff meeting.) Researchers also found that staying up an extra hour, even if followed by a full night’s sleep, is correlated with slower performance the next day. But going to bed an hour earlier than normal has a negligible effect.

The study appeared today on — an online repository for scientific papers in the fields of math and science.

"The data set is pretty amazing," says Jamie Zeitzer, PhD, a co-author of the study and a Stanford assistant professor of psychiatry and behavioral sciences. "We looked at more than 30,000 people over 18 months, which came out to more than 3 million nights of sleep analyzed."

The study — led by Tim Althoff, a Stanford PhD student in computer science, during a summer 2016 internship with Microsoft Research in Redmond, Washington — is thought to be the largest to date to measure the effect of "real-world sleep on performance."

To measure cognitive performance, researchers examined the subjects’ keystroke speed on a computer and their click interactions on a web search engine. Those results were correlated with sleep data collected from wearable fitness devices.

As Zeitzer explains in a blog post about the study by Microsoft’s research group:

Searching the web requires your brain to do a few complex tasks: Figure out what terms to search on, type the query and then process the results to decide which one to click. Even small differences in the amount of time it would take you to click on the result are indicative of how rapidly you are processing that information. The idea is people have slower processing speeds as they get more tired.

Results showed that over the first 24 hours, having one insufficient night of sleep is associated with 1.2 percent slower performance on average keystroke timing. Two insufficient nights of sleep are 4.8 percent slower compared to two nights with longer than six hours of sleep each (2.7 percent and 7.3 percent increases for click times respectively.) The study adds: "These effect estimates took into account any real-world behavioral compensation such as increased caffeine intake that would help improve performance after sleep loss."

The research is another example of the use of mobile technology allowing researchers to collect much larger data sets in real-world time than through traditional studies. More from Zeitzer:

The web-scale study provides insight into the impact of sleep deprivation in the real world, where people compensate for lost sleep with extra coffee and naps, and otherwise adapt to life circumstances that limit pillow time. The findings largely overlap with results from small and controlled lab-scale studies, where participants are systematically sleep deprived and assessed on standardized tests.

Previously: New research uncovers secrets in the brains of sleeping seniors, How to tell if you're sleep deprived and Researchers exploring the effect of sleep loss on health
Photo by Varvara

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