Measurement of non-restorative sleep in insomnia: A review of the literature.

OBJECTIVE Non-restorative sleep (NRS) is a core symptom of insomnia, typically defined as a subjective feeling of being unrefreshed upon awakening. NRS symptoms have been less consistently studied than other symptoms of insomnia, and there is no consensus regarding measurement of NRS. Given its subjective nature, patient-reported outcome (PRO) instruments are important for evaluating NRS symptom severity and treatment-related changes. The objective of this literature review was to identify PROs used in insomnia populations that purport to measure NRS, and to evaluate their psychometric characteristics. METHODS A comprehensive review of PRO instruments used in insomnia was conducted; instruments were reviewed for NRS content by two independent reviewers; a total of 26 instruments identified to contain NRS content were retained for further review. RESULTS Of the 26 instruments reviewed, 23 contained at least one item evaluating subjective nighttime aspects of NRS; 17 contained at least one item evaluating daytime aspects of NRS. Only the Sleep Assessment Questionnaire contained a specific NRS domain score. However, little published evidence was available regarding measurement properties of the NRS domain in insomnia populations. CONCLUSIONS There is currently no reliable and well-validated PRO instrument available for specifically evaluating NRS symptom severity and response to interventions in insomnia populations. Reliable and valid measurement tools are needed to measure the symptom of NRS in insomnia.