Pittsburgh Sleep Quality Index

The Pittsburgh Sleep Quality Index (PSQI) is a self-report questionnaire that assesses sleep quality over a 1-month time interval. It consists of 19 individual items generating seven “component” scores: subjective sleep quality, sleep latency (i.e., how long it takes to fall asleep), sleep duration, habitual sleep efficiency (i.e., the percentage of time in bed that one is asleep), sleep disturbances, use of sleeping medication, and daytime dysfunction. The questionnaire has been used in many settings, including research and clinical activities, and has been used in the diagnosis of sleep disorders. Developed by researchers in the University of Pittsburgh, the PSQI is intended to be a standardized sleep questionnaire for clinicians and researchers to use with ease. The survey contains 19 questions, each weighted on a 0-3 interval scale. A global PSQI score is taken from the survey, with lower scores correlating to better sleep quality. Clinical studies have found the PSQI to be reliable and valid in the assessment of sleep problems to some degree, but more so with self-reported sleep problems and depression-related symptoms than actigraphic measures.

Development and history

In 1988, the PSQI was developed to create a standardized measure designed to gather consistent information about people's sleep. It gained popularity as a measure that could be used in research with people who had sleep disorders, and also to look at how sleep might be associated with depression and bipolar disorder. The PSQI is currently available in 56 languages and because the measure is short and available for free, it has gained popularity as a tool for both research and clinical use. Due to the subjective nature of sleep quality, the PSQI was developed to try and standardize scores across groups for clinicians and patients to more easily interpret. This instrument has been deemed both reliable and valid in determining "good" and "poor" sleep quality.

Scoring and interpretation

The items measure several different aspects of sleep, offering seven component scores. Traditionally, the items from the PSQI have been summed to create a total score to measure overall sleep quality. However, a three factor scoring structure has also been proposed. These factors include Sleep Efficiency (using Sleep Duration and Sleep Efficiency variables), Perceived Sleep Quality (using Subjective Sleep Quality, Sleep Latency, and Sleep Medication variables), and Daily Disturbances (using Sleep Disturbances and Daytime Dysfunctions variables).

Impact

The PSQI now is used by researchers working with people from adolescence (ref) to late life (ref). The PSQI is recommended in independent reviews (ref) because it has accumulated a substantial amount of research evidence (pubmed search), is translated into more than 50 languages (Pitt site) and is available at no charge.

Limitations

The PSQI suffers from the same problems as other self-report inventories in that scores can be easily exaggerated or minimized by the person completing them. Like all questionnaires, the way the instrument is administered can have an effect on the final score.