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What the PHQ-9 actually is

The Patient Health Questionnaire-9 (PHQ-9) is a nine-item self-report tool designed to assess the presence and severity of depressive symptoms over the preceding two weeks. It was developed by Kroenke, Spitzer and Williams and first published in 2001. [1] Each item maps onto one of the nine diagnostic criteria for major depressive disorder in the DSM, and each is scored on a four-point frequency scale: not at all (0), several days (1), more than half the days (2), or nearly every day (3). Total scores therefore range from 0 to 27.

The authors proposed severity bands that have since become widely adopted in primary care: scores of 1–4 indicate minimal symptoms, 5–9 mild, 10–14 moderate, 15–19 moderately severe, and 20–27 severe. [1] A cut-off of 10 or above is commonly used as a threshold for considering further evaluation for major depression in clinical settings. [2]

The PHQ-9 is one of the most widely used screening instruments in the world. The NHS recommends it as a routine outcome measure in IAPT (Improving Access to Psychological Therapies) services. [3] Its brevity, free availability and established psychometric properties have made it a reference point far beyond primary care — including, increasingly, in digital mental health.

What the PHQ-9 is not

This point matters, and it is worth being direct about it: the PHQ-9 is a screening and severity-monitoring instrument, not a diagnostic tool. A clinician diagnoses depression through a full clinical assessment that takes into account the questionnaire score alongside history, context, differential diagnoses and professional judgement. A number on a scale cannot do that work.

Screening tools exist to flag who might benefit from further attention. A high score means “this person warrants a closer look”, not “this person has major depressive disorder”. A low score does not rule out depression, particularly in people who minimise their symptoms or who are having a relatively better fortnight. Kroenke and Spitzer themselves were clear that a positive screen should prompt “further evaluation” rather than automatic treatment decisions. [1]

Apps that present PHQ-9 scores as diagnoses — or even imply it — are misrepresenting the tool. The same applies to apps that use PHQ-style items without being transparent about what the scoring means and what it does not.

Why apps are drawn to PHQ-style questionnaires

Digital mental health apps face a genuine tension. Users often want to understand how they are doing in terms that feel meaningful, not just a colour-coded mood wheel. Structured questionnaires offer a way to track something more specific than a daily emoji rating — they surface patterns in cognitive and somatic symptoms that a simple mood slider would miss.

There is also growing evidence that ecological momentary assessment — capturing self-reported data repeatedly and in context — can surface clinically relevant patterns that retrospective questionnaires miss. [4] Apps are, in principle, well-suited to repeated, low-burden measurement over time. That is genuinely useful.

The PHQ-9 and its shorter derivative, the PHQ-2, are attractive reference points because their psychometric properties are well-documented and their item wording is familiar to clinicians. If a user exports their data or shares it with a GP, a PHQ-9-referenced score is legible in a way that a proprietary seven-point mood scale is not.

What a responsible app can do with PHQ-style data

Keeping the limitations above clearly in mind, here is what a mobile app can do responsibly:

• Track severity over time. Repeated scores give the user — and potentially their clinician — a longitudinal picture. A rising score over several weeks is a more meaningful signal than a single snapshot.
• Prompt a conversation. An app can encourage a user whose scores are elevated to speak to a GP, therapist or trusted person. That is not diagnosis; it is appropriate signposting.
• Surface patterns for clinical sharing. If a user is already in therapy or working with a GP, having structured data to share can make those conversations more productive. [5]
• Signpost crisis support. This is not optional — it is an ethical obligation, addressed in the next section.

What a responsible app cannot do: diagnose, prescribe, promise that scores will change, or substitute for professional care when a user is in distress.

The safety obligation around item 9

Item 9 of the PHQ-9 asks how often, over the past two weeks, the respondent has been bothered by “thoughts that you would be better off dead or of hurting yourself in some way.” [1] Any non-zero response to this item in a clinical setting triggers immediate further assessment. In a digital context, it requires at minimum an immediate, clear and localised route to crisis support.

The Samaritans in the UK, the Crisis Text Line, and equivalent services in other countries exist precisely for this moment. An app that surfaces PHQ-style item 9 content and then does nothing — or routes generically to a help page — is failing the user at the most critical point. Localised crisis routing (showing relevant numbers based on the user’s country) is the minimum responsible standard.

This is not a fringe edge case. Research consistently shows that thoughts of self-harm are more common in the populations most likely to use mental health apps. [6] Building crisis safety into the questionnaire flow is not optional engineering; it is a core product obligation.

The clinical handoff problem

There is a broader structural limitation that apps cannot engineer their way around: the gap between identifying that someone may need help and that person actually receiving it. An app can flag elevated scores and signpost services. It cannot book a GP appointment, guarantee a referral, or provide the therapeutic relationship that underpins effective treatment for depression. [7]

Being honest about this gap is part of responsible app design. The goal of a PHQ-9-informed feature in an app should be to make the path to care clearer and less daunting — not to position the app as a substitute for that care. Apps that blur this line do users a disservice, particularly those whose scores suggest they genuinely need professional support.

Transparency about what is and is not the PHQ-9

Some apps use the PHQ-9 verbatim and present scores using the validated severity bands. Others create questionnaires inspired by the PHQ-9 — drawing on its item structure and theoretical basis without using the exact validated instrument. Both approaches can be legitimate, but they require different levels of transparency with the user.

If an app uses the PHQ-9 verbatim, it should make clear that the resulting score is a screening indicator, not a diagnosis, and that users should discuss scores with a clinician. If an app uses a questionnaire inspired by the PHQ-9, it should be honest that the tool is not the validated instrument itself and that scores are not directly comparable to clinical PHQ-9 data. Conflating the two — or presenting a proprietary tool as if it were the validated measure — is misleading.

MoodFire’s Wellbeing Reviews in context

MoodFire’s optional Wellbeing Reviews are questionnaires inspired by recognised measures such as the GAD-7 and PHQ-9. They are not the validated instruments themselves, and MoodFire does not claim to administer or be validated on the PHQ-9. The feature exists to give users a periodic, structured look at how they have been feeling — a complement to daily mood check-ins rather than a clinical assessment.

Where responses indicate elevated distress, the app routes to localised crisis signposting rather than leaving the user with a number and no context. Wellbeing Review results feed into the Insights view alongside mood trends, so users can see how their structured scores sit alongside their day-to-day patterns. There is also a clinician-friendly PDF export that allows users to share recent patterns with a therapist or GP if they choose to do so.

MoodFire is a CBT self-help app. It is not therapy, not a diagnostic tool and not a substitute for professional care. The Wellbeing Reviews are one tool among several — designed to structure self-awareness, not to replace a clinical conversation.