Psychometric properties of the Insomnia Severity Index for people with chronic obstructive pulmonary disease

Insomnia is one of the most commonly reported symptoms among people with chronic obstructive pulmonary disease (COPD). Prior research evaluated the psychometric properties of the Insomnia Severity Index (ISI) with various populations, but no studies have examined the measurement properties of the instrument in the COPD population. This study aimed to determine the reliability and validity of the ISI for the COPD population.

This study included 96 people with COPD and insomnia. As psychometric properties, the ISI's internal consistency, factor structure, and criterion validity were examined with this sample. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were used to evaluate construct validity. Correlations between scores for the ISI and for measures of depression, anxiety, fatigue, and dyspnea were examined to determine criterion validity.

The Cronbach's alpha value for the ISI was 0.79, indicating good internal consistency. In the EFA, a single ISI factor with an eigenvalue of 3.19 accounted for 45.6% of the variance. CFA indicated adequate construct validity, and interference of sleep problems with daytime functioning and level of distress caused by sleep difficulties showed the highest factor loadings (both 0.78). Criterion validity was supported by significant, weak to moderate correlations between scores for the ISI and for measures of depression, anxiety, fatigue, and dyspnea.

The results provide evidence that the ISI has good reliability and validity for measuring insomnia severity in the COPD population.