If you are experiencing a number of symptoms yourself, or perhaps you recognise some of the signs in a family member or a friend, online self-assessment tests for depression may be helpful in evaluating its severity.
The NHS has an excellent, easy to use, mood assessment questionnaire, which screens for symptoms of both depression and anxiety. It can be found here.
The CESD-R measures symptoms of depression as defined by the American Psychiatric Association’s Diagnostic and Statistical Manual (DSM-IV). An online version is available here.