Zung Self-Rating Depression Scale Calculator

How does this Zung Self-rating Depression Scale (SDS) calculator work?

This health tool assesses depression in young and adult patients with depressive disorder. It consists of a twenty item self assessment questionnaire based on a Likert scale of answers.

Some of the questions are formulated in a positive manner and the scale is weighted in one direction while other questions are formulated negatively with the scale being weighted in the other direction.

Items 1, 3, 4, 7, 8, 9, 10, 13, 15, 19 are scored:

1. A little of the time;
2. Some of the time;
3. Good part of the time;
4. Most of the time.

For items 2, 5, 6, 11, 12, 14, 16, 17, 18, 20 the scale is reversed, as follows:

1. Most of the time;
2. Good part of the time;
3. Some of the time;
4. A little of the time.

The items in the Zung Self-rating Depression Scale (SDS) calculator cover most of the relevant depression symptoms in the four areas: the pervasive effect, the physiological equivalents, psychomotor activities and other disturbances:

■ Depressed mood;

■ Morning symptoms;

■ Crying;

■ Insomnia;

■ Diminished appetite;

■ Weight loss;

■ Sexual interest;

■ Constipation;

■ Palpitations;

■ Fatigue;

■ Clouded reasoning;

■ Difficulty with completing tasks;

■ Difficult decision making;

■ Restlessness;

■ Lack of hope;

■ Irritability;

■ Diminished self esteem;

■ Life satisfaction;

■ Suicidal ideation;

■ Anhedonia.

As a test for depression, the Zung SDS has been through several validations and its discriminatory power is reflected in comparison with normal controls, i.e. subjects achieving significantly higher results are often diagnosed with clinical depression. However, the scale should only have indicative and clinical monitoring purposes, for diagnosis other investigations are required.

SDS score interpretation

As explained above, each of the 20 items indicates the patients assessment of their current depression related experiences and the answers are weighted from 1 to 4. The overall score ranges from 20 to 80 and is often transformed in a SDS Index score of 25 to 100.

The conversion to the SDS Index (towards a 100 point scale) is preformed by using the following formula:

SDS Index = Raw score x 1.25

The consensus for both systems is that the higher the score, the more severe the depression symptoms, as exemplified in the table below:

Other depression tests to use

There are several types of online tests addressing depressive disorder and its multiple facets. The following three are a selection of what you can find readily available:

■ The Major depression index (MDI) calculator – screens for presence and severity of disorder by taking into account day to day activities, feelings and most common symptoms. The assessment is based on frequency and the subject needs to recall the past two weeks.

■ The Depression test by TheCalculator.co – is organized in four sections, each addressing different depression symptoms and signs. The result is a likeliness percentage of suffering from a mental disorder.

■ The Geriatric depression scale (GDS) test – is one of the most reputable and well established methods of evaluation depressive symptoms in elderly patients. There are two versions available, one complete: comprising of 15 questions and one simplified: comprising of 4 direct questions.

References

1) Zung WW. (1965) A Self-Rating Depression Scale. Arch Gen Psychiatry; 12:63-70.

2) Zung WW, Richards CB, Short MJ. (1965) Self-rating depression scale in an outpatient clinic. Further validation of the SDS. Arch Gen Psychiatry; 13(6):508-15.

3) Biggs JT, Wylie LT, Ziegler VE. (1978) Validity of the Zung Self-rating Depression Scale. Br J Psychiatry; 132:381-5.

4) Carroll BJ, Fielding JM, Blashki TG. (1973) Depression rating scales. A critical review. Arch Gen Psychiatry; 28(3):361-6.