Zung Self-Rating Depression Scale

The Zung Self-Rating Depression Scale (SDS) is a 20-item self-report measure designed to assess depressive symptoms in people aged 16 years and over. It assesses the frequency with which the respondent has experienced the depressive symptoms most commonly seen in clinical practice and used in diagnostic criteria for depressive disorders.

Example Zung SDS Items

The Zung SDS assesses four key, clinically relevant depressive symptom domains, as identified by factor analyses (e.g., Romera et al., 2008):

• Core Depressive, which primarily reflects emotional or affective symptoms of depression. This subscale includes items measuring depressed affect, crying spells, decreased libido, hopelessness, personal devaluation, emptiness, suicidal rumination, and dissatisfaction.
• Cognitive, which reflects altered cognitive function including decreased concentration and speed of response. This subscale includes items assessing confusion, psychomotor slowing, indecisiveness, and fatigue.
• Anxiety, which captures symptoms commonly associated with anxiety disorders that frequently co-occur with depression. This subscale includes items measuring sleep disturbances, psychomotor agitation, and irritability.
• Somatic, which addresses physical manifestations of depression. This subscale includes items assessing decreased appetite, weight loss, and tachycardia (fast heart rate).

This multidimensional structure reflects the multifaceted nature of depression and aligns with clinical observations that depression manifests through affective, cognitive, anxious, and somatic symptoms. The inclusion of anxiety-related symptoms is particularly relevant in clinical settings, where co-occurring depression and anxiety is common among clients.

The Zung SDS provides clinicians with valuable information about a client’s overall depressive symptoms as well as their specific symptom profile, which can help inform case formulation and guide treatment planning and targeted interventions. It is also useful for tracking changes in depressive symptoms over time and monitoring response to treatment.

The Zung Self-Rating Depression Scale (SDS) provides a Total Score reflecting the overall frequency with which the respondent has experienced depressive symptoms in the past “several days,” with higher scores indicating higher frequency.

The respondent’s Total Score is expressed as a Community Percentile based on normative data for people aged 16 years and over in the general population (Knight et al., 1983), contextualising their score relative to the typical scores of people aged 16 years and over overall. For example, the 50th percentile represents the typical/“Normal” level of depressive symptoms among people aged 16 years and over, while scores on the 90th percentile fall within the top 10% when compared to people aged 16 years and over and are indicative of “Mild to Moderate” depressive symptoms.

Scores are also provided for the four factors (subscales) identified by Romera and colleagues (2008):

• Core Depressive (Items 1, 3, 6, 14, 17, 18, 19, and 20), which primarily reflects emotional or affective symptoms of depression.
• Cognitive (Items 10, 11, 12, and 16), which reflects altered cognitive function including decreased concentration and speed of response.
• Anxiety (Items 4, 13, and 15), which captures symptoms commonly associated with anxiety disorders that frequently co-occur with depression.
• Somatic (Items 5, 7, and 9), which addresses physical manifestations of depression.

The scoring approach uses qualitative descriptors to categorise the Total Score and subscale scores. Each descriptor corresponds to a specific range of Index Scores (Zung, 1973). An Index Score is calculated by dividing the Raw Score by the maximum possible Raw Score on the scale/subscale, and multiplying by 100. This standardises the scores and enables direct comparisons between subscales. The descriptors and corresponding Index Score ranges are as follows.

• “Normal” – Index Score between 25 and 49
• “Mild to Moderate” – Index Score between 50 and 59
• “Moderate to Severe” – Index Score between 60 and 69
• “Severe” – Index Score between 70 and 100

On first administration, a graph is presented showing the respondent’s Total Index Score and Index Score for each subscale.

If administered more than once, longitudinal graphs are presented for the respondent’s Total and subscale Index Scores, which is useful for monitoring any changes in depressive symptoms over time and treatment progress and outcomes.

A graph is also presented comparing the respondent’s Total Index Score to the normative distribution of Zung SDS scores among 1,125 people aged 16 years and over in the general population and 1,049 clients of a psychiatric outpatient clinic, with shaded areas corresponding to scores between the 25th and 75th percentile (Holmes et al., 1988; Knight et al., 1983). This graph contextualises the respondent’s score relative to the typical level of depressive symptoms among people aged 16 years and over overall and those presenting for treatment in mental health clinics.

The Zung Self-Rating Depression Scale (SDS) has demonstrated sound psychometric properties across numerous studies, including good reliability, good convergent and discriminant validity, and a clinically meaningful, multidimensional factor structure.

Reliability – Knight and colleagues (1983) reported a Cronbach’s alpha of 0.79 in a sample of 1,125 people aged 16 years and over from the general population, indicating good internal consistency and supporting the scale’s reliability for assessing depression.

Validity – The Zung SDS has demonstrated good convergent validity with other established measures of depression; for example, Zung (1965) found a correlation of 0.65 between the Zung SDS and the Minnesota Multiphasic Personality Inventory (MMPI) Depression scale. In terms of discriminant validity, Zung (1965) reported that people with depressive disorders had significantly higher scores compared to non-depressed controls, demonstrating that the Zung SDS can effectively differentiate between these groups.

Factor Structure – Romera and colleagues (2008) conducted a factor analysis on the Zung SDS in a sample of 1,049 primary care patients diagnosed with major depressive disorder (MDD) and found a clinically meaningful four-factor solution: (i) core depressive, (ii) cognitive, (iii) anxiety, and (iv) somatic.

The ability of the Zung SDS to capture the multifaceted nature of depression makes it a valuable tool for comprehensive assessment of depressive symptoms in clinical settings.

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