Iowa Sleep Blog

How Accurately Do Personal Fitness Monitors Measure Sleep?

Monday, June 02, 2014
The proliferation of personal fitness monitors used to measure sleep has prompted researchers to study the accuracy of these devices.

Dr. Montgomery Downs, a sleep researcher at West Virginia University, conducted a study designed to evaluate the reliability and validity of the Fitbit when compared with the polysomnography and standard actigraphy tests used by sleep doctors for diagnosis of most sleep disorders.

Her study involved 24 health adults who wore both Fitbits and actigraphs during standard overnight polysomnography at the West Virginia University’s sleep research laboratory. Both the Fitbits and actigraphs measure sleep by tracking movement.

The study’s primary finding was that both Fitbit and the actigraph overestimated overnight sleep time when compared with results of the lab test. Fitbit exceeded the results of the lab test by 67 minutes and the actigraph by 43 minutes. “These devices say you are asleep more often than you accurately are,” Dr. Downs concluded.

Another study, presented at a sleep researcher’s meeting in November 2013, found the opposite effect in children. The tracker underestimated how long the children were asleep by 109 minutes.

It should come as no surprise that many sleep specialists feel uncomfortable giving someone a clean bill of “sleep health” based solely on data from these devices. These specialists also advise consumers to avoid putting too much trust in the devices to accurately monitor sleep, especially consumers who have sleep disorders.

Learn more at free webinar
Find out more about the pluses and minuses of personal fitness monitors during a free webinar conducted by Dr. Stephen Grant of Iowa Sleep. The webinar will take place from 12-12:30 p.m. on Thursday, June 5. Register at