The Glasgow Sleep Impact Index (GSII): a novel patient-centred measure for assessing sleep-related quality of life impairment in Insomnia Disorder.

OBJECTIVES: Daytime dysfunction and quality of life impairment are important and salient consequences of poor sleep in those with insomnia. Existing measurement approaches to functional impact tend to rely on non-specific generic tools, non-validated scales, or ad hoc single scale items. Here we report the development and validation of the Glasgow Sleep Impact Index (GSII), a novel self-report measure which asks patients to generate, and assess, three domains of impairment unique to their own individual context. These three patient-generated areas of impairment are ranked in order of concern (1-3; i.e. 1=the most concerning impairment), and then rated on a visual analogue scale with respect to impact in the past two weeks. Patients re-rate these specified areas of impairment, post-intervention, permitting both individual and group-level analyses. METHODS: One-hundred and eight patients (71% female; Mean age=45 yrs) meeting Research Diagnostic Criteria for Insomnia Disorder completed the GSII, resulting in the generation of 324 areas (ranks) of sleep-related daytime and quality of life impairment. Fifty-five patients also completed the GSII pre- and post-sleep restriction therapy. The following psychometric properties were assessed: content validity of generated domains; relationship between ranks of impairment; and sensitivity to change post-behavioural intervention. RESULTS: Content analysis of generated domains support recent DSM-5 proposals for specification of daytime consequences of insomnia; with the most commonly cited areas reflecting impairments in energy/motivation, work performance, cognitive functioning, emotional regulation, health/well-being, social functioning and relationship/family functioning. Preliminary results with 108 patients indicate the GSII to have excellent face and construct validity. The GSII was found to be sensitive to change, post-behavioural treatment (p<0.001; Cohen's d≥0.85 for all three ranks of impairment), and improvements were associated with reductions in insomnia severity in both correlational (range of r=0.28-0.56) and responder versus non-responder analyses (all p<0.05). CONCLUSIONS: The development of the GSII represents a novel attempt to capture and measure sleep-related quality of life impairment in a valid and meaningful way. Further psychometric and clinical evaluation is suggested.