Zung SDS: Self-Rating Depression Scale

What this assessment is

The Zung Self-Rating Depression Scale, or Zung SDS, is a 20-item self-report measure of depressive symptoms. William W. K. Zung introduced it in 1965.

The original publication describes a brief rating scale for the affective, psychological, and physical features associated with depression. The result reflects symptom burden. It is not a diagnosis.

Who it was designed for

The SDS was developed for adults. It has been used in clinical screening and research, including studies of people receiving care and community samples.

Its age matters. The scale predates current diagnostic systems and many newer depression measures. A result should therefore be interpreted with evidence from the relevant population, not as a universal rule.

How it is administered

The SDS is completed by the respondent. The standard form asks about experiences over the past several days and uses four response levels for each of 20 items.

Ten items are phrased in one scoring direction and ten in the opposite direction. This balance is part of the original form. A translated, shortened, or altered version may not produce a comparable score.

The AHRQ instrument summary describes the standard self-administered format and its four broad symptom areas.

What it measures

The SDS combines several kinds of depressive symptoms into one total. The AHRQ summary groups them into pervasive emotional effects, physical equivalents, other disturbances, and psychomotor activity.

One total can be useful for screening or tracking. It does not show which symptom group drove the result, and it does not explain the cause.

How scoring works

Each response contributes 1 to 4 points. Ten items are reverse scored before all 20 values are added.

This produces a raw score from 20 to 80. The raw total can then be converted to an index from 25 to 100 by multiplying it by 1.25.

The two systems are easy to confuse. An index score of 50 equals a raw score of 40. A scoring review found that studies have sometimes applied the index cutoff to the raw total by mistake.

Raw is not index.

Always label the result as raw or index. A number without that label cannot be interpreted safely.

The sources reviewed for this page do not establish one universal rule for missing responses. Complete data are preferable. If a study or service uses a missing-item method, it should state that method with the result.

How to interpret a Zung SDS score

A common reporting convention uses the 25-to-100 index:

• 25 to 49: below the original screening boundary
• 50 to 59: mild range
• 60 to 69: moderate range
• 70 to 100: severe range

These are descriptive index bands reported in the AHRQ scale summary. They are not raw-score bands, and they do not confirm a depressive disorder.

The boundary is not universal. A later cutoff study found that the original raw-score boundary performed poorly in its samples. It also describes higher values proposed in Chinese and Australian research.

Context controls the cutoff.

Use the scoring convention and cutoff validated for the population and purpose. Do not switch between raw and index values or treat one boundary as suitable for every setting.

A score does not replace a safety check

The SDS includes a death-related item. A total score must never override concern about that response or a person's immediate safety.

Safety comes first.

Review the response directly and consider the person's current thoughts, intent, plan, means, protective factors, and support. A low total does not make a concerning response unimportant.

What the score cannot tell you

The SDS cannot diagnose depression or determine its cause. It cannot distinguish a depressive disorder from grief, physical illness, medication effects, sleep problems, or another mental health condition.

It also cannot select a treatment. Diagnosis and care decisions require a clinical assessment that considers symptoms, functioning, history, safety, and the person's priorities.

Evidence and limitations

The 1965 development paper established the original scale. Later studies have tested it in different languages, ages, and settings, but their preferred cutoffs have not been consistent.

That disagreement is clinically important. It shows why a score needs its version, scoring system, population, and purpose attached. The SDS can support screening and symptom tracking, but it should not carry the full weight of a diagnostic decision.