The PHQ-9 measures depression symptoms over two weeks and reports one 0-to-27 total. The DASS-21 measures depression, anxiety, and stress over one week and reports three separate 0-to-42 scores. Use the questionnaire that matches the clinical question. Do not convert scores between them.
Neither questionnaire diagnoses a condition or chooses treatment.
The distinction matters.
Side-by-side comparison
| Feature | PHQ-9 | DASS-21 |
|---|---|---|
| Main focus | Depression symptoms | Depression, anxiety, and stress domains |
| Scored items | 9 | 21, with 7 in each domain |
| Timeframe | Past 2 weeks | Past week |
| Survey Doctor output | One 0-to-27 total | Three separate 0-to-42 scores |
| Score calculation | Add the 9 item values | Add each domain, then multiply it by 2 |
| Direct safety item | Yes, item 9 | No |
The original PHQ-9 study supports its 0-to-27 total and five symptom bands. The official DASS scoring guidance explains the three domains and the DASS-21 multiplier.
What the PHQ-9 adds
The PHQ-9 asks how often nine depression symptoms occurred during the past two weeks. It gives one total. That total has five descriptive bands, from minimal through severe.
One score.
Item 9 asks about thoughts of death or self-harm. Any answer above zero needs direct follow-up, regardless of the total. The PHQ-9 is not a complete suicide risk assessment, so the score cannot replace a safety conversation.
If you need help now. In the US, Call 988 or text 988. Call 911 if you are in immediate danger. Outside the US, contact your local emergency number or find support in your country.
Survey Doctor also offers an optional functional-difficulty question after any scored PHQ-9 symptom is endorsed. The answer is stored separately and never changes the 0-to-27 total.
What the DASS-21 adds
The DASS-21 asks how much 21 statements applied during the past week. It gives three scores:
- Depression, including low positive emotion and motivation
- Anxiety, with more emphasis on physical arousal and panic-like experiences
- Stress, including tension, irritability, and trouble relaxing
Three domains.
The official DASS overview describes these as related but distinct dimensions. The anxiety domain is not a general worry score, and the stress domain describes tension rather than stressful events themselves.
Each domain begins as a 0-to-21 raw sum. The official DASS-21 method doubles that value to place it on a 0-to-42 scale. Survey Doctor already performs the multiplication for a native result.
Do not double it again.
The DASS-21 has no direct suicide or self-harm item. A separate safety process is still needed.
Safety still matters.
Why the scores cannot be converted
The questionnaires differ in symptoms, timeframe, structure, and score range. They overlap on some experiences, but the numbers do not share a unit.
No conversion exists.
A DASS-21 depression score cannot be turned into a PHQ-9 total. A PHQ-9 result also cannot fill in the DASS-21 anxiety or stress domains. Keep each questionnaire name with every result, and never place the two scores on one trend line.
Keep them separate.
The score guides explain the conventions in more detail: read the DASS-21 guide or read the PHQ-9 guide.
Check the scoring convention first
A native Survey Doctor DASS-21 result requires all 21 answers and displays all three doubled domain scores. Manual entry requires all three whole-number, already-doubled values. An outside worksheet may instead show undoubled 0-to-21 sums, so confirm the convention before comparing results.
Check first.
Use one convention.
Survey Doctor does not report a DASS-21 grand total. The official FAQ describes a composite method for some professional uses, but that method is not part of this product's result. Do not create a plain sum of the three displayed domains and treat it as a supported Survey Doctor output.
A manually entered PHQ-9 total preserves only the number. It cannot confirm the nine answers, completion, item 9 status, or functional response. Native item-level results provide more context.
How to choose
Purpose comes first.
Choose the PHQ-9 when depression symptoms are the focused question and a direct safety item belongs in the workflow. Choose the DASS-21 when three separate distress domains are useful and the setting already has an independent safety process.
Then plan the review. Consider the answers, daily functioning, safety, history, medical factors, and the person's concerns. A band is a description, not an instruction to start, stop, or change care.
The bottom line
The PHQ-9 gives one focused depression total over two weeks. The DASS-21 gives three already-doubled distress scores over one week. Pick the structure that answers the question, keep the score systems separate, and add clinical and safety context before acting on either result.