Zung Self-Rating Depression Scale SDS
Zung Self-Rating Depression Scale SDS overview
Creator and Context
The Zung Self-Rating Depression Scale (SDS) is a 20 item self report measure of depression, published by William Zung in 1965.
It is one of the earliest self report depression scales and remains in wide use. Its defining characteristic, and its defining hazard, is that it uses two different scores: a raw score and a converted index score.
Presenting Conditions
The 20 items cover the affective, cognitive and physiological symptoms of depression. Ten items are negatively worded and ten are positively worded and reverse scored.
There are no formal subscales.
Administration
Self administered in five to ten minutes. Each item is rated from None, or a little of the time (1) to Most, or all of the time (4), in relation to the past week.
Desired Audience
Adults. It is used both to screen for depression and to grade its severity.
The Zung SDS has sixty years of use behind it and a large comparative literature, which is why services with long running datasets still rely on it. Where you need continuity with historic data, that matters.
Considerations
The raw versus index confusion is the defining hazard of this instrument. A review of papers published between 2010 and 2015 found that in up to 51 percent of studies using a cut off, index score criteria were incorrectly applied to raw scores. Any implementation must be unambiguous about which score is displayed and which bands apply.
Zung's original cut off has poor specificity by modern standards. At the original raw cut off of 40, specificity was only 57 percent.
The 1965 norms are dated.
Copyright status is not clearly documented. It is widely reproduced, but no authoritative rights statement was located. Confirm before commercial deployment.
It is a screening instrument, not a diagnosis.
How to score the Zung Self-Rating Depression Scale SDS
Conducting the assessment
The person rates 20 items from 1 to 4 for the past week. Ten positively worded items are reverse scored.
Interpretation
Items are summed to give a raw score from 20 to 80. Zung's method then converts this to an index score by multiplying the raw score by 1.25, giving a range of 25 to 100.
Zung's severity bands apply to the index score:
Below 50 normal
50 to 59 mild depression
60 to 69 moderate to marked
70 or above severe to extreme
Zung's positive screen threshold was an index of 50, which is a raw score of 40. Contemporary evidence (Dunstan and Scott, 2019) concludes that this is too low, and recommends a raw score of 50 as the threshold for clinical significance.
Clinical Considerations
Be explicit about which score you are looking at. Applying the index bands to a raw score will under identify depression substantially.
Consider the contemporary evidence when choosing a threshold. The original cut off produces a great many false positives.
Use it as a screen, and follow a positive result with assessment.
Zung Self-Rating Depression Scale SDS use cases
Screening for depression in adults
Grading depression severity
Continuity with services and datasets that have used it historically
Research
Category
Depression
Research Summary
Zung, W. W. K. (1965). A Self-Rating Depression Scale. Archives of General Psychiatry, 12(1), 63 to 70.
Dunstan, D. A., & Scott, N. (2019). Clarification of the cut off score for Zung's Self-rating Depression Scale. BMC Psychiatry, 19, 177.
Dunstan, D. A., & Scott, N. (2018). Assigning clinical significance and symptom severity using the Zung scales: Levels of misclassification arising from confusion between index and raw scores. Depression Research and Treatment, 2018, 9250972.
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Note on Assessment licensing
Some assessments are copyright protected and require a licence or the copyright holder's permission for clinical, commercial or digital use. Where that applies, obtaining and maintaining that permission is the responsibility of the practice or organisation using the assessment. Tacklit provides the digital administration, scoring and reporting. We do not grant, transfer or supply rights to the underlying instrument.
