STUDY OBJECTIVE

Cognitive Behavioral Insomnia Therapy (CBT-I) is the gold standard insomnia treatment and the Insomnia Severity Index (ISI) is a frequently used treatment outcome measure. The ISI has strong psychometric properties and is purported to measure perceived insomnia symptom severity. However, little is known about the factors that drive insomnia severity perception and the psychometric properties of the ISI post-CBT-I.

METHODS

Participants were treatment-seeking adults meeting DSM-5 Insomnia Disorder criteria (n = 203, ages 18-77, M = 45.95 years). Participants completed sleep and mood questionnaires, including the ISI, pre- and post-CBT-I. They completed daily Consensus Sleep Diaries each morning throughout two pre-treatment weeks, eight weeks of treatment and two weeks post-treatment. A hierarchical regression analysis examined what predicted post-CBT-I ISI scores and Cronbach's alpha was computed to examine post-treatment reliability of the ISI.

RESULTS

The regression analysis revealed that lower post-treatment ISI scores were associated with lower pre-treatment ISI, and greater decreases in fatigue and generalized anxiety symptoms. The model did not significantly improve when pre-treatment sleep effort or changes in sleep diary indices were added. The post-treatment ISI Cronbach's alpha was .88.

CONCLUSIONS

Although the ISI has been shown to have sound psychometric properties, clinicians should consider that post CBT-I ISI scores are not related to their sleep improvements. Instead, they seem to be related to whether patients perceive themselves as poor sleepers pre-treatment and whether they felt less tired and anxious after CBT-I. Researchers should consider the impact of factors other than sleep when using the ISI at post-treatment. Patients are telling us that CBT-I should focus on addressing symptoms of fatigue and general anxiety; perhaps CBT-I could be improved further to address these concerns more effectively.

SUMMARY

This investigation shows that when individuals are rating their symptom severity after CBT-I, they are also integrating how they felt before treatment and whether they experienced a change in their fatigue or anxiety.