Reliability and validity of Insomnia Severity Index in clinical insomnia patients

Objective To test the reliability and validity of the Chinese version of Insomnia Severity Index(ISI-C) in patients with insomnia. Methods One hundred and twenty patients with insomnia were selected from Zhongshan Hospital Affiliated to Dalian University. The subjects had completed the ISI-C scale and Pittsburgh Sleep quality Index(PSQI) scale, Epworth Sleepiness Scale(ESS) at the same time. The reliability and validity of the scale were tested by Cronbach α coefficient, item correlation analysis, exploratory factor analysis and ROC curve test. Results The Cronbach α coefficient of the ISI-C was 0.804,the test-retest reliability was 0.887 (P<0.01). The items of ISI-C scale were correlated with the corresponding items of PSQI (r=0.831, P<0.01), ESS(r=0.218, P<0.05). Two common factors were extracted by factor analysis including the severity of insomnia and the influence of insomnia, and the cumulative contribution rate was 63.117%(P<0.01).When the cutting point was 10.5 points, the sensitivity and specificity were 84.0% and 92.3%, respectively (P<0.01). Conclusions ISI-C scale is a reliable and valid instrument. It can be used to measure the insomnia of patients in hospitals. Key words: Insomnia; Reliability; Validity