Psychometric Evaluation of the Insomnia Severity Index in Nurses.

OBJECTIVES

Examine psychometric properties of the Insomnia Severity Index (ISI) in a sample of nurses.

METHOD

In a sample of day shift nurses ( = 289), a confirmatory factor analysis (CFA), convergent and discriminant validity analyses, and a test-retest reliability analysis were performed.

RESULTS

CFA showed that a two-factor model provided the best fit. The ISI had moderate to poor convergent validity with sleep diary parameters, and moderate convergent validity with the Sleep Condition Indicator ( = -.66), Pittsburgh Sleep Quality Index ( = .66), and PROMIS Sleep-Related Impairment measure ( = .67). The ISI demonstrated good discriminant validity with the measures Composite Scale of Morningness ( = -.27), Nightmares Disorder Index ( = .25), PTSD Checklist for DSM-5 (sleep items removed;  = .32), and Perceived Stress Scale ( = .43). The ISI had weaker discriminant validity with the PHQ-9 ( = .69) and Generalized Anxiety Disorder Screener ( = .51). The ISI demonstrated a good test-retest reliability (ICCs = .74-.88).

CONCLUSIONS

The ISI is a psychometrically strong measure for the assessment of insomnia severity in day shift nurses. Overlap with psychological symptoms, primarily anxiety and depression, suggests caution while interpreting these constructs.