Validation of the Insomnia Severity Index (ISI) for identifying insomnia in young adult cancer survivors: comparison with a structured clinical diagnostic interview of the DSM-5 (SCID-5)

Objectives: Insomnia is a common problem affecting young adult cancer survivors (YACS) even years after treatment, yet it often goes unidentified and untreated. The Insomnia Severity Index is a widely-used insomnia measure, but has not been studied as an insomnia screener for YACS. The goal of this study was to validate the ISI in YACS by determining its utility in identifying YACS with insomnia disorder diagnosed with the Structured Clinical Interview for the DSM-5 (SCID-5).

Methods: 250 YACS completed the ISI and SCID-5 Insomnia Module. Area under the curve (AUC) was calculated to reflect the ISI's discrimination between YACS with and without SCID-5 insomnia disorder. An ISI cut-off score with sensitivity ≥0.85 and specificity ≥0.75 was deemed acceptable.

Results: Of 250 participants, 52 met criteria for SCID-5 insomnia disorder diagnosis. The ISI had excellent discrimination, with an AUC = 0.91. A cut-off score ≥8 met study clinical screening criteria with sensitivity of 0.85 and specificity of 0.77. A cut-off score ≥7 with a higher sensitivity (0.96) but lower specificity (0.70) was noted as a potential alternative. Cut-off scores ≥12 and ≥ 14 were recommended for applications prioritizing overall accuracy.

Conclusions: Results support validity of the ISI for identifying YACS with insomnia disorder. For clinical screening, data support the use of an ISI cut-off score ≥8 in YACS, and additional cut-off scores were found for research purposes or higher sensitivity. Results of this study and prior studies of the ISI offer important reminders that cut-off scores derived from different populations are not generalizable.