Assessment of sleep problems with the Insomnia Severity Index (ISI) and the sleep item of the Patient Health Questionnaire (PHQ-9) in cancer patients

OBJECTIVE: The objectives of this study were to examine sleep problems in cancer patients, to test the psychometric properties of the Insomnia Sleep Index (ISI) in comparison with the sleep item of the Patient Health Questionnaire-9 (PHQ-9), and to analyze disrupting factors which might cause the sleep problems. METHODS: A sample of 1026 mixed-site cancer patients in treatment at a German oncological rehabilitation clinic was examined. RESULTS: The reliability of the ISI was very good (Cronbach’s alpha = 0.92), and the results of the confirmatory factor analysis were acceptable. Females reported worse sleep quality (ISI mean: 13.7 ± 6.6) than males (10.7 ± 6.4). Sleep problems as measured with the PHQ-9 sleep item were markedly higher than those in the general population (effect size d = 1.15). Patients reported that, of the factors that disrupted their sleep, psychological factors (brooding, worries) were more relevant than symptom factors (pain, nocturnal urination, or restless legs). CONCLUSIONS: The ISI is effective in detecting sleep problems in cancer patients. Normative studies with the ISI would be helpful for assessing ISI mean scores. Sex differences should be taken into account when groups of patients are compared. The sleep item of the PHQ-9 can be used in epidemiological studies.