Pittsburgh Sleep Quality Index (PSQI)

The Pittsburgh Sleep Quality Index is a nineteen item questionnaire that scores self reported sleep over the previous month. It produces seven component scores covering subjective quality, latency, duration, efficiency, disturbances, medication use and daytime dysfunction, summed into a global score from 0 to 21.

A widely used cut off is a global score above 5, which distinguishes poor sleepers from good sleepers with reasonable sensitivity. It has been in use since 1989 and is one of the most cited instruments in sleep research.

It matters because it captures something objective measures miss. Polysomnography records what the brain did; the PSQI records what the person experienced, and those diverge routinely, particularly in insomnia, where the felt experience of sleep is the actual complaint.

Its limitations follow from the same feature. It is self reported and retrospective over a month, so it is subject to recall bias, and it correlates only moderately with objective sleep measures. It is a screening and research tool rather than a diagnosis.

It is also the reason many sleep studies report improvements that a wearable would not see. An intervention can improve perceived sleep quality substantially without changing total sleep time, which is a genuine result rather than a placebo dismissal.

That gap between measured and experienced sleep is worth remembering when reading any sleep claim, including tracker marketing, which reports the measurable and ignores the experienced.

In practice, if your sleep feels poor over weeks, that experience is data rather than an impression, and it is worth taking to a GP whether or not a device agrees.