Depression is a leading worldwide cause of illness burden affecting more than 300 million people and is the 4th leading cause of disability of all ages according to the World Health Organization, while projected estimates suggest that by 2020 depression will be the 2nd leading cause of disability worldwide (World Health Organization [WHO], 2001). Year prevalence in U.S. is approximately 7% (DSM-5; American Psychiatric Association, 2013; Kessler, Wai, Demler & Walters, 2005) and in Europe approximately 4% (Alonso, 2004).
Prevalence varies across countries, however, a recent meta-analytic study, which included cross-sectional studies from all five continents, reports that on average the prevalence of Major Depression Disorder (MDD) or subthreshold depression symptoms is approximately 27% (Wang et al., 2017). MDD occurs significantly more among women than among men, whereas significantly higher at risk of depression are the age groups 30-40, elderly population and people who suffer from chronic physical illnesses. Although occurrence of depression and subthreshold depressive symptomatology in younger population (<30 years old) is found to be the lowest, prevalence is still as high as 20% (Wang et al. 2017).
The symptoms of depression differ from usual sadness or mood changes that people experience in their everyday lives. People with Major Depression Disorder experience depressed mood for almost all day or all day and everyday or almost everyday, or experience severely diminished interest/pleasure in all or almost all activities, as well as a series of other symptoms, such as fatigue, psychomotor retardation, agitation, inability to concentrate, inappropriate guilt, feelings of worthlessness. Symptoms of depression may also include anhedonia (inability to feel pleasure), avolition (diminished volition), alogia (diminished speech) and flattened affect. In addition, Major Depression may be presented with psychotic features (DSM-5). The assessment of symptoms and diagnosis of depression require mental health clinical expertise. Depending on the severity of depression, treatment may involve from psychoeducational interventions to low or high intensity psychological intervention, medication and combined therapy for patients with chronic physical illnesses.
Alonso, J. et al. (2004). Prevalence of mental disorders in Europe: results from the European Study of the Epidemiology of Mental Disorders (ESEMeD) project. Acta Psychiatrica Scandinavica, 109 (Suppl. 420), pp. 21–27. doi: 10.1111/j.1600-0047.2004.00327.x
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.) Washington, DC; London, England: American Psychiatric Publishing.
Kessler, R. C., Chiu, W. T., Demler, O. & Walters, E. E., (2005). Prevalence, Severity, and Comorbidity of 12-Month DSM-IV Disorders in the National Comorbidity Survey Replication. Archives of General Psychiatry, 6, pp. 617-627. doi: 10.1001/archpsyc.62.6.617
Wang, J. (2017). Prevalence of depression and depressive symptoms among outpatients: a systematic review and meta-analysis. British Medical Journal, 7(8). doi:10.1136/bmjopen-2017-017173
World Health Organization. (2001). The world health report 2001. Mental Health. New Understanding. New Hope. Geneva WHO. Retrieved from http://www.who.int/whr/2001/en