What Are the PSQI and ISI? Two Sleep Assessments Explained in Plain English
If you've ever sat in a therapist's office or filled out intake paperwork and been handed a questionnaire about your sleep, then there's a good chance it was one of two things: the Pittsburgh Sleep Quality Index or the Insomnia Severity Index.
These are the two most widely used sleep assessment tools in clinical practice. And while they're both asking about your sleep, they're actually measuring different things and used for different purposes.
Whether you're a client who just got a score and wants to understand what it means, or a clinician brushing up on behavioral sleep medicine tools, here's a plain-language breakdown of both.
The Pittsburgh Sleep Quality Index (PSQI)
What is it?
The Pittsburgh Sleep Quality Index or PSQI was developed in 1989 by researchers at the University of Pittsburgh and has since become one of the most widely used sleep quality measures in the world. It’s a 19-item self-report questionnaire that takes about 5-10 minutes to complete.
The PSQI is designed to assess overall sleep quality over the past month. It’s not just looking at whether you have insomnia, but taking a broader look at how well you’re sleeping across multiple dimensions.
What does it measure?
The PSQI scores seven different components of sleep:
Subjective sleep quality — how would you rate your sleep overall?
Sleep latency — how long does it take you to fall asleep?
Sleep duration — how many hours are you actually sleeping?
Sleep efficiency — what percentage of your time in bed are you actually asleep?
Sleep disturbances — how often are you waking up, too hot, in pain, nightmares, etc.?
Use of sleep medication — are you relying on anything to sleep?
Daytime dysfunction — how is poor sleep affecting your ability to function during the day?
How is it scored?
Each of the seven components is scored from 0-3, giving a total score range of 0-21. The lower the score, the better the sleep quality.
PSQI Scoring:
0-5: good sleep quality
6-10: poor sleep quality, worth addressing
11-21: significant sleep disturbance, clinical attention recommended
A score above 5 is the clinical cutoff for poor sleep quality. If you scored above that and have been brushing it off as “just how I sleep” your body has been telling you something worth listening too. Now, some folks will just always be over 5 and still have good sleep due to clinical comorbidities, but best to discuss your score with a qualified professional.
How is it used clinically?
The PSQI is commonly used as a baseline screening tool and it gives a broad snapshot of sleep health and helps clinicians identify which dimensions of sleep are most disrupted. It’s used in research, clinical intakes, and to track change over time during treatment. Because it covers a full month of sleep and multiple components, its useful for understanding the bigger picture before diving into a targeted intervention like CBT-I.
The Insomnia Severity Index (ISI)
What is it?
The Insomnia Severity Index was developed by Dr. Charles Morin and is a 7-item questionnaire that typically takes under 5 minutes. Where the PSQI gives a broad overview of sleep quality, the ISI is more focused. It’s designed to detect and measure the severity of insomnia.
It’s also one of the primary tools used to track progress during CBT-I treatment, making this relevant if you’re working with a sleep therapist.
What does it measure?
The ISI looks at seven areas:
Difficulty falling asleep
Difficulty staying asleep
Problems waking too early
Satisfaction with current sleep patterns
How noticeable sleep problems are to others
How worried or distressed you are about sleep
How much sleep problems interfere with daily functioning
How it is scored?
Each item is rated on a 0-4 scale, with a total score range of 0-28.
ISI Scoring:
0-7: no clinically significant insomnia
8-14: subthreshold insomnia (mild but worth monitoring)
15-21: moderate insomnia (clinical intervention recommended)
22-28: severe insomnia (treatment strongly recommended)
A score of 15 or above is the threshold for moderate to severe clinical insomnia. A score of 8-14 lands in a “subthreshold” zone. It may not meet full clinical criteria for insomnia disorder, but it’s a sign that sleep quality is being meaningfully affected and is worth taking seriously.
How is it used clinically?
The ISI is used in three main ways in clinical practice:
Screening: identifying whether someone meets criteria for insomnia disorder
Treatment planning: understanding which specific aspects of insomnia are most severe and need to be targeted
Progress monitoring: administering it at regular intervals during CBT-I to track whether the interventions are working
For therapists specifically: the ISI is one of the most efficient and well-validated tools for demonstrating treatment outcomes in CBT-I. If you’re integrating sleep work into your practice, administering the ISI at intake and at the close of treatment gives you clear, quantifiable evidence of client’s progress.
PSQI vs ISI - What’s the Difference and When is Each Used?
The simplest way to think about it:
PSQI gives you a broad picture of sleep quality across multiple dimensions over the past month. It’s the wide-angle lens.
ISI zooms in specifically on insomnia, how severe it is, how distressing it is, and how much it’s impacting your life. It’s a precision tool.
In practice, clinicians use both. They complement each other well and together give a much fuller picture than either tool alone.
How These Tools Connect to CBT-I Treatment?
If you’re starting CBT-I, or considering it, you’ll likely encounter both of these assessments. Here’s how they fit into the process:
At intake, both tools help establish a baseline, giving your therapist a clear, quantified picture of what’s happening with your sleep before treatment begins.
During treatment. Seeing a score drop from a 20 to a 9 over six weeks is genuinely motivating and it gives both the client and therapist objective evidence that the work is working.
At completion, both tools are used to document treatment outcomes, which matters both for the client’s confidence in their progress and for clinicians who need to demonstrate effectiveness.
Your Score is a Starting Point, Not a Verdict
If you’ve taken one of these assessments and your score is high, that’s not a life sentence. It’s information. It tells you and a trained clinician where to focus, what’s most disrupted and what kind of support is going to be most useful.
Insomnia is one of the most treatable sleep conditions we have, especially with CBT-I. A number on a questionnaire is just the beginning of the conversation.
What to Talk Through What Your Score Means?
Whether you’ve just scored high on one of these assessments, you’re a therapist looking to integrate sleep measurement into your practice, or you’re simply ready to address your sleep with someone who knows CBT-I inside and out, I can help.
I offer virtual CBT-I therapy for Illinois and Texas residents. I also provide CBT-I consulting for therapists. Contact me today and let’s figure out what your sleep actually needs.
