Depression is the most commonly occurring psychological problem in the United States, with several estimates putting the number of depressed people at roughly twenty percent of the US population. While this percentage may not seem extraordinarily large on its face, as a number it may add up to sixty million people, or one in every five US citizens. Common though it may be, depression often goes undiagnosed and many depressed people may not actually be aware of their condition, while other people may suspect that they're depressed but may not be entirely certain.

Though it's reasonable and even wise to get diagnosed for depression by a mental health professional, other means for determining depression exist that can be carried out completely on one's own, outside of any type of clinical environment. These methods specifically take the form of personally assessing depression by participating in a self-assessment test. Self-assessment tests for depression are quite common, and in fact are often used in professional settings during efforts to make a mood disorder diagnosis. Studies have found that people are typically quite honest in answering questions about their mood, and this may be especially true when answering questions in written form.

Depression self-assessment tests aren't some arbitrary question and answer form: they are typically simple to perform, but have been designed to be exceptionally accurate in testing for depression and are based upon established psychological principles. In addition to asking particular questions about a person's state, symptom intensity and duration will also be measured by credible depression self-assessment tests. This type of inquiry can often distinguish between genuine depression and other, temporary mood disturbances.

Arguably the most popular of the depression self-assessment tests is the Beck Depression Inventory, or the BDI. Aaron Beck, a psychiatrist and an advocate for cognitive therapy, developed the BDI. The BDI came into use in the early 1960's and in the time since has been put under copyright and used on a large clinical scale. There are twenty-one questions on the Beck Depression Inventory, with each question response given a zero to three score for a total of four potential responses. The BDI is completed entirely by the individual being assessed for depression, even when the BDI is performed in a clinical setting.

The Beck Depression Inventory isn't the sole depression self-assessment test, and many psychological resources have developed depression self-assessment tests of their own. Because of the tendency for depression to be expressed in emotional and physical terms, many if not all depression self-assessment tests are broken into assessment for psychological and physical symptoms. The results of the physical and psychological symptoms profile are used in conjunction to form as accurate of a diagnosis of depression as is possible.