Depression scale: PHQ-9 and DASS-21 depression subscale

Depression is a state of prolonged sadness and loss of interest, with changes in sleep, appetite, energy and negative thoughts about oneself. The PHQ-9 follows the 9 DSM-IV diagnostic criteria for depression, while the DASS-21 depression subscale measures hopelessness, lack of motivation and low self-evaluation. Common topics in Vietnam: depression among students, older adults and health workers, and links with phone addiction, social media and social support.

Comparing the scales

Items of each scale

Original English wording from the published source. Replace placeholders such as [system] or [brand] with what your study is about, and pilot the questionnaire with 20 to 30 respondents first.

Depression Severity (PHQ) · PHQ-9 depression scale

Code	Item
PHQ1	Little interest or pleasure in doing things
PHQ2	Feeling down, depressed, or hopeless
PHQ3	Trouble falling or staying asleep, or sleeping too much
PHQ4	Feeling tired or having little energy
PHQ5	Poor appetite or overeating
PHQ6	Feeling bad about yourself—or that you are a failure or have let yourself or your family down
PHQ7	Trouble concentrating on things, such as reading the newspaper or watching television
PHQ8	Moving or speaking so slowly that other people could have noticed? Or the opposite—being so fidgety or restless that you have been moving around a lot more than usual
PHQ9	Thoughts that you would be better off dead or of hurting yourself in some way

Source: Kroenke, Spitzer & Williams (2001). Response scale, licence and APA reference: PHQ-9 depression scale.

Use in the survey kit

Depression (D) · DASS-21 scale

Code	Item
D3	I couldn't seem to experience any positive feeling at all
D5	I found it difficult to work up the initiative to do things
D10	I felt that I had nothing to look forward to
D13	I felt down-hearted and blue
D16	I was unable to become enthusiastic about anything
D17	I felt I wasn't worth much as a person
D21	I felt that life was meaningless

Source: Lovibond & Lovibond (1995). Response scale, licence and APA reference: DASS-21 scale.

Use in the survey kit

Tips

• PHQ-9 is scored 0 to 3 per item, total 0 to 27. Cutoffs 5, 10, 15, 20 correspond to mild, moderate, moderately severe, severe.
• Item PHQ9 asks about thoughts of self-harm. Provide support contacts in the questionnaire; for anonymous online surveys, consider the PHQ-8 (item 9 dropped) as the authors advise.
• The DASS-21 depression subscale score must be multiplied by 2 before comparing with the classification cutoffs.
• Depression surveys usually need prior approval from an ethics board or your supervisor. Check your university's rules.

Once you have a scale, put the concept in the research model drawer to state your hypotheses, work out the minimum sample size, and after data collection check reliability with the Cronbach's alpha calculator.

Frequently asked questions

Can the PHQ-9 be used for Vietnamese students?

Yes, but re-check the structure. Vu et al. (2022) used the PHQ-9 on 899 residents of a suburban area in Vietnam and found a 2-factor structure. Run EFA or CFA and report the structure you find rather than assuming 1 factor.

Can the PHQ-9 diagnose depression?

No. The PHQ-9 is a screening tool. Results only indicate symptom severity; diagnosis needs a doctor or psychologist.

Should depression be reported as a total score or by severity level?

Both. Use the total score for regression or SEM, and report the proportion by severity level in the descriptive statistics.