Zung SDS: Self-Rating Depression Scale

The Zung SDS is a 20-item validated self-report measure of depression covering affective, somatic, psychomotor, and psychological symptoms. Scores expressed as an SDS Index (25–100). One of the most widely used depression scales in clinical research since 1965.

What the Zung SDS measures

The Zung Self-Rating Depression Scale (SDS) was developed by William W. K. Zung at Duke University Medical Center in 1965, making it one of the earliest validated self-report measures of depression. Zung designed it to quantify depression based on a dimensional model, covering affective, physiological, psychomotor, and psychological symptoms across 20 items.

Each item is rated on a 4-point frequency scale (1–4). Ten items are negatively worded and scored directly; ten are positively worded and reverse-scored. The raw total (20–80) is converted to an SDS Index by multiplying by 100/80. An SDS Index of 50 or above indicates the presence of depression. The scale covers 20 characteristic signs and symptoms of depression, including sad affect, crying, sleep disturbance, appetite change, and hopelessness.

Check the copyright holder's terms before clinical or commercial use. The Zung SDS has been translated into over 30 languages. While the PHQ-9 is now more commonly used in primary care settings, the Zung SDS remains a reference standard in longitudinal research and is useful where a classic scale is required for comparison with historical data.

How to administer the Zung SDS

The Zung SDS is a self-report questionnaire that respondents complete independently, without clinician administration, which makes it practical for screening in primary care and research. Each of the 20 statements is rated on a 4-point frequency scale from 1 (a little of the time) to 4 (most of the time). A clinician should review the results before any diagnostic conclusion.

Rate how each statement applies to you right now or over the past several days.

Educational reference only. Cannot diagnose or replace clinical evaluation.

Zung SDS scoring and interpretation

Zung (1965). SDS Index = (raw score / 80) × 100. Raw scores range from 20 to 80. Use the score interpreter above to look up an Index: below 50 is the normal range, 50–59 mild, 60–69 moderate to marked and 70 or above severe. These ranges are a commonly used clinical convention.

Psychometric properties

• Validity (Biggs et al., 1978): In 26 depressed outpatients treated with a tricyclic antidepressant, the Zung SDS correlated 0.69 with the treating physician's global rating; in 41 patients it correlated highly with the Hamilton Rating Scale, and it distinguished four severity groups.
• Spanish version (Ruiz-Grosso et al., 2012): In 194 patients in Lima, Peru, Cronbach's alpha was 0.89 and the area under the ROC curve was 0.84 for separating major depression from other psychiatric disorders and 0.96 for separating it from no psychiatric disorder (optimal cut-offs, as reported in that study, of ≥47 and ≥45).
• Older adults (Jokelainen et al., 2019): In 520 community-dwelling adults aged 72–73 in Finland, the area under the curve was 0.85; the optimal cut-off point of 39 gave a sensitivity of 79.2% and specificity of 72.2%, with a positive predictive value of 12.5% and a negative predictive value of 98.6%.

Limitations

• Screening, not diagnosis. The Zung SDS quantifies depressive symptoms; a diagnosis needs a clinical evaluation.
• Cutoffs vary. Optimal cut-offs differ across languages, ages and settings, and the Index bands are a convention.
• Low positive predictive value in community samples. In older community adults, most positive screens were false positives (PPV 12.5%).
• Self-report. Results depend on the respondent's recall and candour.

Measuring depression in HiBoop

HiBoop does not offer the Zung SDS; this page is reference material. For depression, HiBoop offers the PHQ-9 and PHQ-8, with automated scoring and tracking over time.