PHQ-9 calculator (depression severity score)

How this PHQ-9 calculator works

This PHQ-9 calculator adds the nine answers of the Patient Health Questionnaire-9, each scored from 0 to 3, to give a total from 0 to 27. The PHQ-9 is the depression module of the Patient Health Questionnaire, a self-administered version of the PRIME-MD instrument, and its nine items follow the nine DSM-IV criteria for major depression. Each item asks how often, over the last 2 weeks, the patient has been bothered by a problem: not at all (0), several days (1), more than half the days (2) or nearly every day (3). Kroenke, Spitzer and Williams validated it as a severity measure in the Journal of General Internal Medicine in 2001, in 6,000 patients from 8 primary care and 7 obstetrics-gynecology clinics, with an independent mental health professional interview in 580 of them. Internal consistency was high, with a Cronbach's alpha of 0.89 in primary care and 0.86 in obstetrics-gynecology, and test-retest correlation was 0.84.

The PHQ also has a separate diagnostic algorithm. It suggests major depressive syndrome when five or more items are answered at least "more than half the days" and one of them is item 1 or item 2, and other depressive syndrome with two to four such items; item 9 counts if present at all. Before a diagnosis, Kroenke 2001 expects the clinician to rule out physical causes of depression, normal bereavement and a history of a manic episode. This calculator reports the severity total only. A tenth question asks how difficult the problems have made work, home life or getting along with other people; the PHQ manual says it is not used in calculating any PHQ score but reflects the patient's overall sense of impairment.

Worked example from the PHQ instruction manual: a 43-year-old woman who looks sad and has had fatigue for a month answers 3, 1, 2, 3, 1, 2, 3, 0 and 1 to items 1 to 9. Three items at 1, two at 2 and three at 3 give a total of 16, moderately severe. These are the answers loaded in the calculator above. Her item 9 answer of 1 is flagged; in the manual, the physician's questioning found no significant suicidal potential.

PHQ-9 score interpretation

PHQ-9 score interpretation uses the five severity bands from Kroenke 2001: 0–4 minimal, 5–9 mild, 10–14 moderate, 15–19 moderately severe and 20–27 severe. In that study, as the PHQ-9 total rose, functional status fell on all six scales of the SF-20 health survey, while symptom-related difficulty, sick days and health care use rose. Against the mental health professional interview, a total of 10 or more had a sensitivity of 88% and a specificity of 88% for major depression, and the area under the ROC curve was 0.95. Of the 41 interviewed patients with major depression, 88% scored 10 or more, while 93% of those with no depressive disorder scored below 10. The PHQ instruction manual calls a score of 10 a yellow flag, drawing attention to a possible clinically significant condition, and 15 a red flag, where active treatment is probably warranted. The band describes symptom severity and is not a diagnosis on its own.

How the cut-offs performed for major depression:

PHQ-9 item 9: thoughts of self-harm

Item 9 of the PHQ-9 asks how often the patient has been bothered by "thoughts that you would be better off dead or of hurting yourself in some way". Any answer above 0 needs a prompt clinical assessment of self-harm risk, whatever the total score, and this calculator shows a separate note whenever that happens. The PHQ instruction manual says that a final decision about the actual risk of self-harm requires a clinical interview, and it points to a four-item screener, the P4 by Dube and colleagues, for following up a positive answer. The diagnostic algorithm in Kroenke 2001 also treats item 9 differently from the other eight items: it counts if present at all, regardless of duration. A low total can therefore sit alongside a positive item 9, for example a total of 3 with item 9 answered "several days". Simon and colleagues, writing in Psychiatric Services in 2013, showed that the item 9 answer carries risk information of its own.

In 84,418 outpatients aged 13 or over who completed 207,265 questionnaires in one integrated health system, the cumulative 1-year risk of a suicide attempt rose from 0.4% in those answering "not at all" to 4% in those answering "nearly every day", and the risk of suicide death rose from 0.03% to 0.3%. Item 9 remained a strong predictor of suicide attempt after adjusting for age, sex, treatment history and overall depression severity. Risk was not zero with an answer of 0, so a 0 on item 9 does not rule out risk either.

When the PHQ-9 is less reliable

The PHQ-9 is a self-report questionnaire, so the total depends on how the patient reads and answers nine items about the last 2 weeks, and it does not replace a clinical assessment. Kroenke 2001 notes that before a diagnosis the clinician is expected to rule out physical causes of depression, normal bereavement and a history of a manic episode, none of which a score can do. Accuracy also depends on the reference standard: in the Levis 2019 individual participant data meta-analysis of 58 studies and 17,357 participants, sensitivity across cut-offs of 5 to 15 was 5% to 22% higher against semistructured interviews than against fully structured ones. The PHQ-9 seemed similarly sensitive but possibly less specific in younger than in older patients, although the authors concluded that a cut-off of 10 or above can be used regardless of age. Kroenke 2001 was carried out in US primary care and obstetrics-gynecology clinics, where 7% of the interviewed sample had major depression.

The PHQ manual adds that many translations are linguistically validated, but few have been checked against an independent structured psychiatric interview. A total also hides which symptoms drive it, so read the individual answers as well as the sum.