Research method
Patient Health Questionnaire (PHQ-9)
The PHQ-9 is a nine-item self-report instrument for depressive-symptom severity, not a treatment. Papers in this set use it as an eligibility threshold (often PHQ-9 ≥10), as a primary outcome (mean change, response, remission, reliable improvement), and as a reference scale against which a new mood measure is correlated. GAD-7 often travels with it; a PHQ-9 benefit without a GAD-7 benefit — or the reverse — is a result, not a rounding error.
Anxiety- and depression-treatment studies need a shared severity language. PHQ-9 answers 'how do these symptoms score on a standard questionnaire at this week?' Its main limitation is that a falling score is not a mechanism, a single-arm drop to PHQ-9 <5 is not a randomised effect, and a 2.5-point mean difference can coexist with a non-significant remission contrast.
Evidence
What the evidence shows
Drawn from 6 studies in this library. Each finding starts with a plain-language takeaway, then the denser detail. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope with a short note on each study’s contribution. Challenged positions are labeled — they are not findings.
As a reference instrument, PHQ-9 correlated with a brief mobile Immediate Mood Scaler at r=.59 (GAD-7 r=.57) among 110 clinical and community adults. That cross-sectional correlation supports complementary in-the-moment monitoring; it does not show that IMS improves treatment outcomes, and the mixed epilepsy/community sample is not routine outpatient anxiety care.
Randomised PHQ-9 contrasts in this set are modest-to-moderate and endpoint-specific. Kokoro-app adjunctive CBT in 164 participants with antidepressant-refractory major depression scored about 2.5 PHQ-9 points lower at week 9 (SMD 0.40) with more response but not significantly more remission. Internet CBT for depression in diabetes (91 with baseline data after screening 106) produced Hedges g=0.78 on PHQ-9 and g=0.72 on GAD-7; 66% completed all six lessons, and 51% of iCBT completers with data showed reliable PHQ-9 improvement versus 18% of treatment-as-usual.
Study Role Design N Population Outcome Can a CBT phone app help stubborn depression? Supports RCTKokoro-app smartphone CBT plus antidepressant switch vs medication change alone N=164 · ITT; primary outcome at week 9 in 163/164 (99.4%) Adults in Japan with antidepressant-refractory major depression PHQ-9 at week 9 iCBT for depression in diabetes Supports RCT6-lesson internet CBT vs treatment-as-usual wait for depression in diabetes N=106 · 49 iCBT, 57 TAU; 91 with baseline data for ITT analyses Adults with diabetes and depression PHQ-9 (and GAD-7 / diabetes distress) at posttreatment IntelliCare used PHQ-9 both to enter and to judge outcome. A single-arm field trial of 105 adults (PHQ-9 ≥10 and/or GAD-7 ≥8) found significant paired-score improvement, with 37% reaching PHQ-9 <5 and 42% GAD-7 <5 by end of treatment. A later 2×2 factorial RCT found PHQ-9 and GAD-7 fell across arms; coaching produced larger GAD-7 reductions than self-guided care, while weekly recommendations strengthened PHQ-9 gains and raised median sessions (median 216; last use day 56). Coaching did not clearly beat self-guidance on depression.
Study Role Design N Population Outcome IntelliCare app suite field trial Supports Human experimentSingle-arm 8-week field trial of IntelliCare Android suite with low-intensity coaching N=105 · PHQ-9 ≥10 and/or GAD-7 ≥8 at enrollment Adults with elevated depression and/or anxiety symptoms PHQ-9 and GAD-7 change over 8 weeks Coaching vs recommendations in IntelliCare Supports RCT2×2 factorial: coaching vs self-guided × weekly app recommendations vs none N=301 · Adults with elevated PHQ-9 or GAD-7 using IntelliCare suite Adults with elevated depression or anxiety symptoms using IntelliCare Android apps PHQ-9/GAD-7 change and app engagement over ~8 weeks PHQ-9 can stay flat. New dementia carers on Talking Point showed no PHQ-9 or GAD-7 change at 12 weeks (61 provided outcomes); 17 of 58 never visited the forum. Among users, more time correlated with greater PHQ reduction, but most individuals showed no reliable symptom change. No control group and low engagement limit any claim that forums treat carer depression.
Open questions
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes — limits on how far one study travels — not a forced fight between papers.
Mean PHQ-9 change, response, remission and 'score <5' are different claims. Kokoro-app's 2.5-point ITT advantage came without a significant remission difference. IntelliCare's uncontrolled 37% below 5 is a threshold count, not a randomised remission rate. iCBT's 51% versus 18% is reliable improvement among completers with data, not the same as g=0.78 on the full ITT sample. Treating those percentages as one 'PHQ-9 worked' statistic collapses the disagreements the papers actually report.
- Can a CBT phone app help stubborn depression?
- IntelliCare app suite field trial
- iCBT for depression in diabetes
Study Role Design N Population Outcome Can a CBT phone app help stubborn depression? Supports RCTKokoro-app smartphone CBT plus antidepressant switch vs medication change alone N=164 · ITT; primary outcome at week 9 in 163/164 (99.4%) Adults in Japan with antidepressant-refractory major depression PHQ-9 at week 9 IntelliCare app suite field trial Supports Human experimentSingle-arm 8-week field trial of IntelliCare Android suite with low-intensity coaching N=105 · PHQ-9 ≥10 and/or GAD-7 ≥8 at enrollment Adults with elevated depression and/or anxiety symptoms PHQ-9 and GAD-7 change over 8 weeks iCBT for depression in diabetes Supports RCT6-lesson internet CBT vs treatment-as-usual wait for depression in diabetes N=106 · 49 iCBT, 57 TAU; 91 with baseline data for ITT analyses Adults with diabetes and depression PHQ-9 (and GAD-7 / diabetes distress) at posttreatment PHQ-9 and GAD-7 do not always move as a pair, and not every digital support changes either. IntelliCare coaching favoured GAD-7 more than PHQ-9; iCBT moved both (g=0.78 and 0.72); the carer forum moved neither overall. Using PHQ-9 as the sole outcome would have missed the factorial trial's clearest coaching signal.
- Coaching vs recommendations in IntelliCare
- iCBT for depression in diabetes
- Dementia-carer internet support forum
Study Role Design N Population Outcome Coaching vs recommendations in IntelliCare Supports RCT2×2 factorial: coaching vs self-guided × weekly app recommendations vs none N=301 · Adults with elevated PHQ-9 or GAD-7 using IntelliCare suite Adults with elevated depression or anxiety symptoms using IntelliCare Android apps PHQ-9/GAD-7 change and app engagement over ~8 weeks iCBT for depression in diabetes Supports RCT6-lesson internet CBT vs treatment-as-usual wait for depression in diabetes N=106 · 49 iCBT, 57 TAU; 91 with baseline data for ITT analyses Adults with diabetes and depression PHQ-9 (and GAD-7 / diabetes distress) at posttreatment Dementia-carer internet support forum Supports OtherObservational pre–post study of new Talking Point dementia-carer forum joiners (not randomised) N=61 · 128 completed baseline; 61 provided 12-week outcomes (primary analytic sample) New informal dementia carers joining an internet support forum PHQ-9, GAD-7, and SQCRC change over 12 weeks
Common misconceptions
PHQ-9 is a treatment for depression or anxiety.
It is a questionnaire. Kokoro-app, iCBT, IntelliCare and Talking Point are interventions; PHQ-9 is how several of them scored symptoms. IMS even uses PHQ-9 as a reference, not as care.
If 37% of users reach PHQ-9 <5, the app remitted depression in 37% of patients.
That figure is from a single-arm IntelliCare field trial with coaching and no control. Expectancy and concurrent care remain alternative explanations. Kokoro-app's randomised 2.5-point gap did not even carry a significant remission contrast.
A significant mean PHQ-9 difference is the same as clinical recovery, and PHQ-9 always tracks anxiety.
Kokoro-app separated response from remission. iCBT's reliable-improvement gap (51% vs 18%) is a completer statistic alongside g=0.78. Coaching in the factorial trial moved GAD-7 more clearly than PHQ-9, so depression-scale success is not automatic anxiety-scale success.
Exam-style questions
Short-answer questions that ask you to explain or compare, not recall.
A methods section says 'the primary outcome was PHQ-9.' Using Kokoro-app and the diabetes iCBT trial, list two different success definitions that sentence could hide.
Mean-score difference (about 2.5 points, SMD 0.40; or Hedges g=0.78) versus binary response/remission or reliable improvement (Kokoro-app response without significant remission; iCBT 51% vs 18% reliable improvement among completers with data). Eligibility can also use PHQ-9 ≥10 without that being the estimand.
Why is IMS r=.59 with PHQ-9 not evidence that replacing clinic PHQ-9 with a momentary scale will improve anxiety treatment?
It is a cross-sectional correlation in 110 mixed clinical/community adults (GAD-7 r=.57). Correlation with a reference questionnaire validates tracking, not a treatment effect. The sample is not a trial of swapping instruments in routine outpatient care.
IntelliCare coaching reduced GAD-7 more than self-guided care but did not clearly beat self-guidance on PHQ-9. What exam mistake does that prevent?
Treating PHQ-9 as a sufficient summary of 'mental health benefit.' In that factorial trial, recommendations helped PHQ-9 and session counts (median 216), while coaching's cleaner signal was anxiety (GAD-7). Pick the scale that matches the claim.
Talking Point did not change PHQ-9 or GAD-7 at 12 weeks, yet more forum time correlated with greater PHQ reduction among users. How can both be true without proving forums treat carer depression?
The overall paired change in 61 completers was null, and 17 of 58 never visited. The time–PHQ correlation is among users, without a control group, so people who feel better may use the forum more (or vice versa). Most individuals had no reliable symptom change.
The studies
6 studies in this library bear on Patient Health Questionnaire (PHQ-9), ordered by citations.
- IntelliCare app suite field trial
Eight weeks of IntelliCare apps plus light coaching produced large pre–post drops in depression and anxiety symptoms.
- Can a CBT phone app help stubborn depression?
Adding a smartphone CBT program to a medication switch improved depressive symptoms more than switching antidepressants alone.
- Coaching vs recommendations in IntelliCare
In a factorial RCT, coaching lowered anxiety more than self-guided use, while weekly app recommendations boosted depression improvement and app sessions.
- iCBT for depression in diabetes
Unmodified clinician-supported iCBT beat treatment-as-usual on depression, anxiety, distress, and diabetes-specific distress in adults with diabetes.
- Dementia-carer internet support forum
Over 12 weeks on Alzheimer’s Society’s Talking Point forum, caregiving relationship quality improved but anxiety and depression scores did not.
- Mobile Immediate Mood Scaler validation
A 22-item mobile Immediate Mood Scaler correlated strongly with standard PHQ-9 and GAD-7 scores in 110 participants.
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