I am wondering if the specific questions asked by the Insomnia Severity Index (ISI) can be analyzed individually. Is anyone aware of articles that do this? Or, using principle components analysis?
I haven't seen the ISI items used individually, but that's not to say it can't be done. The items on the ISI ask about difficulty falling asleep, difficulty staying asleep, difficulty waking too early, satisfaction with sleep, how noticeable one's sleep disturbance is, distress re: sleep disturbance, and interference from sleep disturbance. Many of those items would probably be better measured by the subscales of the Pittsburgh Sleep Quality Index (http://www.sleep.pitt.edu/content.asp?id=1484&subid=2316). It has subscales for duration of sleep, sleep disturbance, sleep latency, daytime dysfunction from sleep problems, and overall sleep quality. I haven't checked the literature, but I bet those subscales have better validity and reliability than the individual items of the ISI.
Brian
Hello,
Insomnia represents something of a challenge to measure because there is no generally accepted reference or gold standard. One approach would be to use a carefully constructed questionnaire which incorporates items relevant to the construct of insomnia, where each component score measure a particular aspect of the same construct of insomnia.The developers of the instrument reported that all seven component scores of the ISI showed satisfactory internal consistency, as indicated by a Cronbach’s alpha.
Principal components analysis of your data can help you factors explaining the most variance in the dataset, the cumulative percentage of explained variance after each factor, and decide how many factors are relevant in your population.
Best regards,
Tatyana
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