2.6. Definition of depression

There exist different forms of depression and depression can manifest itself in different grades of severity. In general, depressive feeling is an emotion that is universally experienced by virtually everyone at some time in life. Depressive feeling can be a normal emotional reaction e.g., in different normative crises during an individual’s life-cycle (Isometsä 1999, Stahl 2001). Depressive feeling can also manifest itself as a special symptom in different mental or somatic disorders (Aalto-Setälä 2002). As an illness, depression is a socially debilitating syndrome including clusters of symptoms (i.e., vegetative, cognitive, behavioural, and physical features as well as impairment of impulse control in behaviour), only one symptom of which is abnormality of mood (Stahl 2001). In depressive disorders, one has lost the sense of control of one’s mood and affects: Patients suffering from depressive disorders might experience loss of energy and interest, they have feelings of guilt/worthlessness, and difficulties in concentrating. They also might have loss of appetite, insomnia or hypersomnia, and frequently experience thoughts of death or suicide/suicidal behaviour. In the most severe form of depression, i.e., major depression with psychotic features, patients also have delusions or hallucinations (Kaplan et al. 1994).

Throughout the history of psychiatry, there have existed a number of different classifications of depression (Tamminen 1993). With regard to diagnosing depression, contemporary epidemiological surveys nowadays usually conceptualize depression as a diagnosis, based on the criteria of diagnostic systems such as DSM-IV (the fourth edition of Diagnostic and Statistical Manual of Mental Disorders) diagnostic classification (American Psychiatric Association 1994) or ICD-10 (International Classification of Disorders) (World Health Organization 1992) as reviewed by Aalto-Setälä (2002). In the DSM-IV, for example, the following depression diagnoses are given: Major depressive disorder, dysthymia, adjustment disorder with depressed mood and depressive disorder not otherwise specified (American Psychiatric Association 1994). In addition to structured or semi-structured diagnostic instruments, there are several rating scales designed to ascertain depressive symptoms, the value of which is well established in obtaining estimates of symptom prevalence in the population and for screening purposes (Aalto-Setälä 2002).