Pittsburgh Sleep Quality Index (PSQI)
A widely used questionnaire that scores self-reported sleep quality over the past month, where higher scores mean worse sleep.
The Pittsburgh Sleep Quality Index, usually shortened to PSQI, is a self-report questionnaire that asks people about their sleep over the previous month. It produces a single global score summarising overall sleep quality, with higher scores indicating worse sleep.
Beyond the global score, the PSQI breaks sleep down into components — including how long it takes to fall asleep (sleep latency), total sleep duration, habitual sleep efficiency (the proportion of time in bed actually spent asleep) and sleep disturbances. This lets researchers see not just whether sleep improved, but which aspects of it changed.
Because it is quick, cheap and well validated, the PSQI is one of the most common outcome measures in sleep research, from exercise trials to studies of shift work. Its main limitation is that it is subjective: it captures how people feel they slept, which does not always match what devices or laboratory measures record.