Insomnia Severity Index (ISI)
Also known as: ISI
The ISI is a 7-item self-report questionnaire designed to assess the severity of insomnia in adolescents and adults. Developed by Morin and colleagues and validated in 2001, it measures difficulty falling asleep, difficulty staying asleep, early morning awakening, and daytime functional impairment due to sleep problems. The ISI is brief (2–3 minutes), psychometrically sound, and widely adopted in sleep research, primary care, and behavioral sleep medicine clinics for screening, baseline assessment, and treatment monitoring.
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When to use it
The ISI is indicated for screening suspected insomnia in primary care, psychiatry, and sleep medicine settings. Use it at baseline to establish insomnia severity and eligibility for intervention, at weekly or monthly intervals during CBT-I or medication trials to monitor treatment response, and at endpoint to quantify improvement. The ISI is NOT a diagnostic tool (diagnostic interviews or sleep medicine evaluation required) but rather a severity measure. It is useful across age groups (adolescents, adults, older adults) and in diverse settings (primary care, specialty sleep clinics, research studies). It is less useful in patients with severe cognitive impairment or illiteracy; consider administering verbally or by telephone interview in such cases.
Strengths & limitations
- Brevity and feasibility: 7 items taking 2–3 minutes to complete, facilitating repeated administration in time-constrained clinical settings or research protocols.
- Strong psychometric properties: excellent internal consistency (Cronbach's α ≥0.90), test-retest reliability (r ≥0.80), and discriminant validity against insomnia diagnostic criteria (AUC ≥0.85).
- Validated across diverse populations: adults, older adults, psychiatric patients, cancer patients, chronic pain populations; 20+ language translations available.
- Sensitive to both pharmacological and non-pharmacological interventions; published MCID ≥7 points and clear cutoff-based remission criteria enable clinically meaningful outcome assessment.
- Endorsed by major sleep medicine and psychiatry societies (American Academy of Sleep Medicine, American Psychiatric Association) as a standard insomnia severity measure.
- Self-report bias: subjective sleep perception may not correlate perfectly with objective sleep duration (polysomnography) or actigraphy; some patients underestimate sleep due to poor sleep quality perception.
- Does not differentiate insomnia subtypes (sleep onset vs. sleep maintenance vs. early morning awakening) separately; subscale analysis not validated, limiting detailed phenotyping.
- Limited assessment of daytime impact: only 2 of 7 items address daytime functional consequences; supplementary functional measures recommended for comprehensive outcome assessment.
- Does not assess sleep-related comorbidities (sleep apnea, restless legs, circadian disorders) that may require differential treatment; diagnostic evaluation necessary.
- Modest ceiling effects in severe insomnia samples; score ranges 0–28, so extremely severe cases cluster at high end, reducing sensitivity to incremental improvement.
Frequently asked
What is the difference between the ISI and the Athens Insomnia Scale (AIS), and which should I use?
The ISI (7 items, 0–4 per item, total 0–28) and AIS (8 items, 0–3 per item, total 0–24) are both brief, validated insomnia severity scales. ISI is more widely used in North America and research; AIS is more common in Europe and primary care. Both have ≥8 cutoff for probable insomnia. ISI is slightly shorter and assesses past 2 weeks; AIS assesses past month. Choose based on availability and clinician familiarity; they are not interchangeable (different score ranges) but both are valid. For research, choose one a priori and stick with it.
Can I use the ISI to screen for sleep apnea or other sleep-related breathing disorders?
No. The ISI measures insomnia (difficulty sleeping, non-restorative sleep) but does not assess sleep apnea symptoms (witnessed apneas, gasping, loud snoring, daytime somnolence, nocturia). Sleep apnea requires formal sleep study (polysomnography or home sleep apnea test). If ISI reveals insomnia symptoms but the patient also reports snoring, witnessed pauses in breathing, or unrefreshing sleep despite adequate sleep duration, refer for sleep apnea screening before starting CBT-I alone.
What change on the ISI indicates successful treatment?
A reduction of ≥7–8 points from baseline or a change from above-threshold (≥8) to subclinical (<8) indicates treatment response. For example, a patient with baseline ISI = 18 (moderate) improving to ISI = 8–10 (subthreshold) shows clinically meaningful improvement. Ideally, aim for ISI <8 (no clinically significant insomnia). Symptom resolution lags behind ISI score change; continue treatment for 4–8 weeks to consolidate gains.
Should I use ISI in children or adolescents with insomnia?
The ISI has been used in adolescents (age 12+) with reasonable validity, but it was developed in adults. For children <12, use age-appropriate sleep quality/insomnia measures (e.g., the Sleep Disturbance Scale for Children, SDSC). Adolescents (13–17) may complete ISI independently; younger children require parental report or clinician assessment.
How do I interpret a low ISI score in a patient who still complains of poor sleep?
ISI reflects subjective sleep complaint intensity and daytime impairment. A low score (≤7) suggests the patient perceives insomnia as mild or not impairing daily function, yet they may still report sleep dissatisfaction. Assess: (1) objective sleep duration via actigraphy or sleep diary (is sleep actually short?), (2) sleep quality perception (feel rested despite sleeping?), (3) daytime function (actually impaired or anxious about sleep?), and (4) comorbidities (depression, anxiety, pain) elevating distress without high ISI. A sleep diary or actigraphy plus qualitative discussion often clarifies the discrepancy.
Can the ISI be used alongside other insomnia measures, like the Pittsburgh Sleep Quality Index (PSQI)?
Yes, but with caveats. ISI measures insomnia severity over the past 2 weeks; PSQI measures sleep quality and dysfunction over 1 month with more items on sleep latency, efficiency, and disturbances. In research, either may be used; for comprehensive sleep assessment, both add value. They are not interchangeable (different timeframes, dimensions), so report both if using both. For clinical practice, ISI is more efficient and preferred for monitoring change.
Sources
- Morin, C. M., Belleville, G., Bélanger, L., & Ivers, H. (2011). The Insomnia Severity Index: Psychometric indicators to detect insomnia cases and evaluate treatment response. Sleep, 34(5), 601–608. DOI: 10.1093/sleep/34.5.601 ↗
- Bastien, C. H., Vallières, A., & Morin, C. M. (2001). Validation of the Insomnia Severity Index as an outcome measure for insomnia research. Sleep Medicine Reviews, 5(5), 377–383. DOI: 10.1016/s1389-9457(00)00065-4 ↗
- Morin, C. M. (2006). Insomnia: Psychological assessment and management. New York: Guilford Press. link ↗
How to cite this page
ScholarGate. (2026, June 3). Insomnia Severity Index (ISI). ScholarGate. https://scholargate.app/en/psychiatry/insomnia-severity-index
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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