Psychometric properties of the Insomnia Severity Index in cancer survivors

Insomnia is commonly associated with cancer treatment. Cancer treatments increase risk for numerous psychological and medical late effects, thus making cancer survivors psychologically and medically vulnerable. Prior research examined psychometric properties of the Insomnia Severity Index (ISI) with various populations, including the French version of the ISI, with participants undergoing active cancer treatment. However, no prior studies examined insomnia exclusively with cancer survivors, using the English version of the ISI.

This study examined internal consistency and factor structure of an English version of the ISI in 100 cancer survivors (M_age  = 51.1; SD = 14.92). This final analytic sample was composed of participants from three different insomnia interventions. Survivors ranged from less than 1 year off treatment (17%) to 21+ years off treatment (6%), with most participants off treatment for 1 to 2 years (24%).

The mean ISI score for the total sample was 16.69 (SD = 4.47), indicating clinical insomnia, with moderate severity. Principal Components Analysis (PCA) indicated two factors (five items loading on Factor I and two items loading on Factor II) and acceptable reliability (α = .73). Item-total correlations ranged from .15 to .63.

Findings support the reliability of the ISI in cancer survivors. However, its factor structure warrants additional research with larger samples of cancer survivors. Results suggest inconsistency across participant responses and that ISI items may be functioning differently with this unique population of cancer survivors. Findings indicate that sleep maintenance problems are central to the experience of insomnia in our survivor sample.