ISI: Insomnia Severity Index

What this assessment is

The Insomnia Severity Index, or ISI, is a seven-item measure of perceived insomnia symptoms and their effect on daily life.

It covers difficulty falling asleep, difficulty staying asleep, waking too early, satisfaction with sleep, daytime interference, how noticeable the problem is, and distress about sleep.

Charles Morin developed the ISI in the 1980s. The original validation study evaluated it as a brief way to measure perceived insomnia severity.

The ISI measures symptoms. It does not diagnose an insomnia disorder by itself.

Who it was designed for

The standard patient form was developed for adults. It has been studied in community, primary-care, and sleep-clinic samples, including people receiving insomnia treatment.

Other respondent forms and translated versions exist. Evidence from one form should not be assumed to apply unchanged to another.

Some later studies include adolescents and specific medical groups. Population, language, setting, and reason for assessment can affect which score boundary performs best.

Confirm the exact form before comparing scores.

How it is administered

The patient version is self-completed. Each of the seven items has five response levels scored from 0 to 4.

The standard recommended recall period is the past month. An official two-week version also exists. Use the same timeframe when comparing repeated results.

Do not silently change the recall period.

The current instrument record distinguishes the patient, clinician, and significant-other forms and records both the one-month and two-week recall versions.

That form label belongs with the score.

What it measures

The ISI combines nighttime sleep difficulty with the person's view of its daytime effect and emotional impact.

It is narrower than a broad sleep-quality measure. The PSQI covers several parts of sleep over the past month, including duration, efficiency, disturbances, medicine use, and daytime dysfunction.

The ISI asks how severe and disruptive insomnia feels.

It does not measure breathing pauses, restless legs, circadian timing, or every possible cause of poor sleep. It also does not replace a sleep history.

One total summarizes all seven areas.

How scoring works

Score each response from 0 to 4. Add all seven values.

The total runs from 0 to 28. Higher totals indicate greater perceived insomnia severity and impact.

There are no reverse-scored items and no separate subscale totals in the standard scoring method.

Complete all seven items when possible. The reviewed sources do not establish one universal rule for replacing a missing answer. Do not treat a blank response as zero.

Use the same version and recall period when tracking change.

How to interpret an ISI score

The common interpretation ranges are:

• 0 to 7: no clinically significant insomnia
• 8 to 14: subthreshold insomnia
• 15 to 21: moderate clinical insomnia
• 22 to 28: severe clinical insomnia

These are descriptive ranges. They do not confirm or exclude a diagnosis.

A 2011 community study found that a score of 10 or more worked well for detecting possible insomnia cases in that sample. That research boundary serves a different purpose from the four descriptive ranges.

Do not mix the two systems.

Review the score with sleep opportunity, duration of the problem, daytime impairment, and the person's health and circumstances.

What the score cannot tell you

The ISI cannot show why sleep is difficult. It cannot separate chronic insomnia from short-term stress, pain, medication effects, depression, sleep apnea, restless legs, circadian problems, or an unsuitable sleep schedule.

It also cannot confirm the frequency and duration requirements used in a clinical diagnosis.

A low score does not rule out another sleep disorder. A high score does not identify one cause or one treatment.

Do not diagnose from the total alone.

Evidence and limitations

The original study found good reliability and expected relationships with sleep diaries and other clinical measures. Later work supported the ISI for case detection and tracking change.

A systematic review of sleep questionnaires found substantial evidence for the ISI while also showing that study methods and populations vary.

The score is subjective. It records the person's experience rather than a laboratory measurement of sleep.

That experience is clinically useful, but it is not the whole assessment.

Version, recall period, language, setting, and missing responses must remain visible when results are compared.