Severity of depression

The severity of depression can vary from person to person. Severity is generally divided as follows:

Severe depression - you would normally have most or all of the nine symptoms listed above. 
Also, symptoms markedly interfere with your normal functioning.
Moderate depression - you would normally have more than the five symptoms that are needed to make the diagnosis of depression.
 Also, symptoms will usually include both core symptoms. 
Also, the severity of symptoms or impairment of your functioning is between mild and severe.
Mild depression - you would normally have five of the symptoms listed above that are required to make the diagnosis of depression.
 However, you are not likely to have more than five or six of the symptoms.
 Also, your normal functioning is only mildly impaired.
Subthreshold depression - this is where you have less than the five symptoms needed to make a diagnosis of depression. 
So, it is not classed as depression.
 But, the symptoms you do have are troublesome and cause distress.

 If this situation persists for more than two years it is sometimes called dysthymia.