Is the PHQ-9 accurate enough to track depression?

In the original validation by Kroenke and colleagues (2001), a PHQ-9 score of 10 or more identified major depression with about 88% sensitivity and 88% specificity. It is a severity measure rather than a diagnosis, but it is accurate enough to follow change over time.

How often should a clinic collect these scores?

A 2017 review by Fortney and colleagues found that tracking helped only when scores were frequent, timely, and reviewed with the patient during the visit. One-time screening and scores that arrived late did not change outcomes.

If tracking helps, why do so few clinics do it?

A 2019 review by Lewis and colleagues found fewer than 20% of behavioral health practitioners track routinely. The barriers sit at the patient, practitioner, organization, and system levels, and so do the fixes, like building the measure into the workflow.

Maintenance

What tools do clinics use to track depression over time?

Last updated October 29, 2026

Short answer

Mostly brief, validated symptom questionnaires that patients complete again and again. The most common for depression is the PHQ-9, and others include the CUDOS. Used within measurement-based care, the same short scale is repeated each visit, so a clinic can watch the trend over time, not just a single snapshot.

The research

Zimmerman, M., Chelminski, I., McGlinchey, J. B., & Posternak, M. A. (2008). A clinically useful depression outcome scale. Comprehensive Psychiatry, volume 49, pages 131 to 140.

Sample More than 1,400 psychiatric outpatients completed the scale at intake, with a separate acceptability study of 100 depressed patients. It validates one measure in United States outpatient clinics, not a trial comparing treatments.

Published 2008

Journal Comprehensive Psychiatry

Mark Zimmerman and colleagues at Rhode Island Hospital built and tested the Clinically Useful Depression Outcome Scale, or CUDOS, a short questionnaire a patient fills in themselves to rate how their depression has been over the past week. It has 18 items and was designed to be quick enough to use at every visit. The team tested it in more than 1,400 psychiatric outpatients who completed it at intake, and ran a separate study of 100 depressed patients to check whether it was practical and acceptable in everyday care. The scale held together well. Repeated testing in 176 patients gave a test-retest reliability of 0.92, where 1.0 would be perfect agreement, and its internal consistency was high. It also measured the right thing. CUDOS scores lined up more closely with another self-report measure of depression than with measures of anxiety, substance use, eating problems, or physical symptoms, and they tracked closely with a clinician's interview rating of how severe the depression was. The authors' point was practical. A measure only gets used if it is short, and a short measure that still agrees with the longer clinician interview gives a clinic a realistic way to score depression again and again over time.

Read the paper

What does this mean for your clinic?

The honest first thing to say is that there is no single official tool. Clinics track depression with brief, validated, patient-completed symptom scales, repeated on a schedule. The PHQ-9 is the most widely used, because it is free, short, and maps onto the recognized criteria for depression. The CUDOS studied here is one well-validated alternative, built for the same job: a quick score the patient can give at each visit.

What the research underneath these tools shares is a simple finding. A short self-report scale can agree closely with a much longer clinician interview. That is what makes routine tracking realistic for a busy clinic. You do not need a trained rater and a long sitting at every appointment. A patient can complete a validated scale in a few minutes, and the score is close enough to the formal rating to guide the conversation that follows.

The tool matters less than the habit. A scale used once at intake tells you where someone started. The same scale repeated every few weeks tells you the direction they are moving, which is the thing you actually want to know. Whichever instrument your clinic picks, the value comes from using one consistently and reviewing the trend with the patient, not from the particular form.

Two limits are worth stating plainly. This was a validation of one measure, mostly in United States outpatient clinics, so the exact figures travel better than they prove. And a symptom score is a severity measure, not a diagnosis. It informs a clinical judgment, it does not replace one. This is also where the gap between visits matters. A score captured only in the appointment shows one day every few weeks. The same validated scale, collected between visits and waiting for your team, is how the trend stays current without taking minutes from the room.

The takeaway

Pick one validated depression scale, such as the PHQ-9 or the CUDOS, and use the same one at every visit. Consistency is what makes a trend readable.
Score on a schedule, not just at intake. One measurement is a starting point, a repeated one shows direction.
Review the trend with the patient in the room, where it can shape the next decision rather than sit in a file.

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Between-session support Mental readiness

This is the work Asendar™ was built for: collecting the same validated scores between visits and keeping the trend in front of your team, so a clinic can watch depression change over time without waiting for the next appointment to take a reading.

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