How people rate their sleep, not their brain waves, was linked with underestimating it
Researchers compared how long 225 adults thought they had slept with how long a sleep-lab recording said they slept. How people rated their sleep quality was more closely linked with underestimating their sleep than anything in their brain-wave recordings.
At a glance
- Many people who have an overnight sleep test think they slept less than the recording shows.
- The people who underestimated their sleep didn't actually sleep less than the others, but they rated their sleep quality differently.
- None of 600 brain-wave measures reliably picked out who would underestimate their sleep.
- Study type
- Look-back study of sleep-lab records from one hospital
- Who took part
- 225 adults in China who had an overnight sleep study for medical reasons
- Published
- Sleep Medicine, 2026
- Strength of evidence
- Early evidence A look-back study at one hospital, with 225 people who were tested for medical reasons. Most of the measures tested showed no clear difference.
What the researchers did
The researchers looked back at the records of 225 adults who had an overnight sleep study in a hospital lab. Each person also said how long they thought they had slept.
They compared each person's own estimate with the time the recording measured, then split people into two groups: those who underestimated their sleep the most, and the rest.
They then checked more than 700 measures to see which ones differed between the groups. These included questionnaires, sleep stages and 600 detailed brain-wave features.
What they found
The two groups slept for about the same time, according to the recordings. What differed was how they rated the quality of their sleep.
None of the brain-wave features clearly separated the groups. Adding them didn't help predict who would underestimate their sleep, compared with a simple model using sleep-quality rating, daytime sleepiness and age.
Even that simple model was only moderately good at telling the groups apart. Sleep apnoea was no more common in one group than the other.
The caveats
- Everyone came from one hospital and was tested for a medical reason, so they may not represent other adults.
- With 225 people, the study may have been too small to spot small differences in brain waves.
- Splitting people into just two groups is a simple approach that can hide differences within each group.
- The study looked back at existing records, so it can't explain why some people underestimate their sleep.
What this could mean for you
It's common to feel you slept less than you did. In this study, that gap was tied to how people judged their sleep, not to anything unusual in their brain waves.
How you feel about your sleep still matters, even if a sleep test looks normal. If you feel you sleep badly, tell your doctor how it feels as well as what any test showed.
The study
Long C, Chen J, Xu X et al. Sleep underestimation and subjective sleep appraisal: Limited value of routine polysomnographic and electroencephalographic features. Sleep Medicine, 2026; 149:109321.
Read the paper (DOI 10.1016/j.sleep.2026.109321) · PubMed
Declared interests: The authors declared no conflicts. Part of the funding came from a research laboratory hosted by Simcere Pharmaceutical Group, which the authors say had no role in the study.