SAN ANTONIO — Three commercially-available sleep tracking devices provide a "reasonable" estimate of total sleep time (TST) in adults, although they tend to slightly underestimate TST compared to self-report, according to a comparative analysis.
The study compared the Fitbit Charge HR (worn on the wrist), the Beddit 2 (placed under the bedsheet), and the ResMed S+ (placed on the nightstand) for accuracy in estimating TST against the clinically-validated actigraphy (Philips Actiwatch-L).
"The devices did fairly well in estimating total sleep time when compared to actigraphy but they did worse when compared to sleep diaries — but nobody should rely just on sleep diaries anymore," lead investigator Thomas Rieck, of the Mayo Clinic Healthy Living Program in Rochester, Minnesota, told Medscape Medical News.
The findings were presented here at SLEEP 2019: 33rd Annual Meeting of the Associated Professional Sleep Societies.
Exponential Rise in Wearables
Use of wearable devices that measure activity and sleep have increased exponentially in popularity in recent years. Actigraphy coupled with a sleep diary have historically been considered a reliable and valid tool for home assessment of sleep, Rieck noted.
In the comparative analysis, 48 adults (mean age 35 years; 73% women) used the three tracking devices for 7 consecutive nights. All of them were good sleepers, as defined by the Pittsburgh Sleep Quality Index (PSQI) of < 5.
During the 7-day study, participants completed the American Academy of Sleep Medicine (AASM) sleep diary. Estimated TST logged by each of the trackers was compared with sleep diaries and actigraphy.
The results showed significant differences in estimated TST between the three devices and the sleep diary, with the devices underestimating TST by 25 to 49 minutes on average.
Table. Estimated TST for Device vs Sleep Diary
| Comparison |
Mean TST (hrs) |
Mean absolute |
P value |
Median Diff |
| Fitbit Charge HR |
7.2 |
-25.0 |
0.5 |
-3.3% |
| Beddit 2 |
7.0 |
-34.4 |
< .001 |
-6.4% |
| Actiwatch-L |
6.9 |
-37.0 |
< .001 |
-9.7% |
| ResMed S+ |
6.7 |
-49.5 |
< .001 |
-9.8% |
When compared against actigraphy, average TST estimated by the Fitbit Charge HR and the Beddit 2 did not differ significantly from actigraphy, while the ResMed S+ estimated mean TST was slightly lower than actigraphy (by 12.8 minutes).
Table. Estimated TST for Device vs Actigraphy
| Comparison |
Mean TST (hrs) |
Mean absolute |
P value |
Median Diff |
| Fitbit Charge HR |
7.2 |
11.8 |
0.12 |
6.5% |
| Beddit 2 |
7.0 |
-5.0 |
0.59 |
3.1% |
| ResMed S+ |
6.7 |
-13.6 |
0.045 |
1% |
"These types of devices will get better over time as we get different and better sensors," Rieck told Medscape Medical News. "It's important to get people to think about their sleep and these devices are a reasonable option for people looking to estimate TST on more than one night," he added. None of the devices seemed to disrupt sleep.
Jesse Cook, a graduate student in the clinical psychology program at the University of Wisconsin-Madison, has also studied wearable sleep trackers.
"First and foremost, anytime people take interest in their sleep is really important, so I think there is a lot of benefit from these consumer sleep trackers and providing real-time feedback," he noted in an interview with Medscape Medical News.
"The design of this study was well done," said Cook. "Most of these devices are reasonable estimations of total sleep time and they provide a lens into circadian sleep-wake patterns. That's useful. However, they cannot be used for diagnosing any kind of sleep disorder, as the AASM recently said in a position statement, and people should not change their behavior just from what one of these devices tells you," said Cook.
The AASM position statement encourages clinicians to become familiar with the technology and outputs of these devices and use them to enhance the clinician–patient relationship.
"The problem is there is an overwhelming number of models," said Cook.
The study was supported by the Mayo Clinic Healthy Living Program. Rieck and Cook have disclosed no relevant financial relationships.
SLEEP 2019: 33rd Annual Meeting of the Associated Professional Sleep Societies: Abstract 1005. Presented June 9, 2018.
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Cite this: Commercial Trackers a Good Gauge of Total Sleep Time - Medscape - Jun 10, 2019.
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