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.