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Abstract
Background: Insomnia is a prevalent health complaint that is often difficult to evaluate
reliably. There is an important need for brief and valid assessment tools to assist
practitioners in the clinical evaluation of insomnia complaints.Objective: This paper
reports on the clinical validation of the Insomnia Severity Index (ISI) as a brief
screening measure of insomnia and as an outcome measure in treatment research. The
psychometric properties (internal consistency, concurrent validity, factor structure)
of the ISI were evaluated in two samples of insomnia patients.Methods: The first study
examined the internal consistency and concurrent validity of the ISI in 145 patients
evaluated for insomnia at a sleep disorders clinic. Data from the ISI were compared
to those of a sleep diary measure. In the second study, the concurrent validity of
the ISI was evaluated in a sample of 78 older patients who participated in a randomized-controlled
trial of behavioral and pharmacological therapies for insomnia. Change scores on the
ISI over time were compared with those obtained from sleep diaries and polysomnography.
Comparisons were also made between ISI scores obtained from patients, significant
others, and clinicians.Results: The results of Study 1 showed that the ISI has adequate
internal consistency and is a reliable self-report measure to evaluate perceived sleep
difficulties. The results from Study 2 also indicated that the ISI is a valid and
sensitive measure to detect changes in perceived sleep difficulties with treatment.
In addition, there is a close convergence between scores obtained from the ISI patient's
version and those from the clinician's and significant other's versions.Conclusions:
The present findings indicate that the ISI is a reliable and valid instrument to quantify
perceived insomnia severity. The ISI is likely to be a clinically useful tool as a
screening device or as an outcome measure in insomnia treatment research.