ref, www/www/www/Articles/Depression-Dx_conversion_Bipolar-AJP-2001.pdf">ref, www/www/www/Articles/Depression-Dx_conversion_Bipolar-Angst-2005.pdf">ref, Manic, Hypomanic, Mixed Episode, Bipolar I, II Disorder, antidepressant, Bipolar Disorder, Major Depression, here, prev"/> Course and Prevalence of Depression | PsychVisit
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Course and Prevalence of Depression

Prevalence of Depressive Disorders

According to American data, Over 20% of all women and over 10% of all men will experience a Major Depressive Episode at least once in their lives [ref]. These rates rise to 25% of all women and 15% of all men when considering any type of Depressive Disorder [ref].  About 8% of women and 5% of men will experience Dysthymia in their lifetimes [ref].  In any one year about 13% of all women and over 7% of all men in the USA are suffering from Depression [ref].   These rates are similar in other Western industrialized nations [ref].

It seems that over the past few decades, the rates of Depression have been steadily on the rise, and Depressive Disorders have been starting-up at progressively younger ages, though the reasons for this remain unknown [ref].  The industrialized and developed nations of the world have the highest rates of Depression [ref].

Course of Depressive Disorders

A Depressive Disorder can first appear at any time in a person's life, whether in childhood or old age.  On average, Depression most commonly starts in the early 20's or 30's [ref].   Once a person has their first Major Depressive Episode, there is a 60% chance that he or she will have another episode within 5 years, and an 85% chance of having another episode in 15 years [ref].  The more episodes that a person experiences, the greater are the chances that he or she will have still more episodes in the future.  On average, people with Major Depressive Disorder have a Major Depressive Episode once every five years [ref].

Usually, Depression is a disorder that is episodic, meaning that once a Depressive episode resolves, the person returns to their usual state of health.  Left untreated, a Major Depressive Episode will normally last about a year, but with treatment about half of all individuals will recover completely within 3 months, and another 15% will improve substantially during this time with a reduction in their symptoms of at least 50% [ref].

However, there is a large proportion of individuals with Depression who remain chronically ill.  About 12% of all individuals with a Depressive episode will not recover from their episode even 5 years after it began [ref]. On average, all people with Major Depressive Disorder will experience lingering depressive symptoms (called sub-syndromal symptoms) about 60% of the time, even when they are not in the midst of a full-blown Depressive Episode [ref].

Impact of Depression on Quality of Life

Depression is one of the world's leading causes of disability [ref], and because it impairs people's ability to concentrate and apply themselves to their regular tasks, it is a major cause of absenteeism and lost productivity at work that tends to exceed most physical illnesses [ref]. Depression also causes a severe impairment in people's overall quality of life and in their ability to remain invested in their family and social roles [ref].

Rates of Diagnostic Change to Bipolar Disorder

Anywhere from 10% [ref] to over 40% [ref, ref] of people originally diagnosed with Major Depressive Disorder will eventually experience a Manic, Hypomanic or Mixed Episode, thus changing their diagnosis to Bipolar I or II Disorder.  If any of these episodes were triggered by the use of an antidepressant, then technically a diagnosis of Bipolar Disorder cannot be made, though the suspicion remains high for this diagnosis. There are certain characteristics that predict which individuals with Major Depression may eventually be found to have an underlying Bipolar Disorder (see here for details).


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Medical Causes

Predictors of Course