You will find the complete explanation below about epidemiology of mood disorders (mania and major depression) in various factor:
   

Sex
An almost universal observation, independent of country or culture, is the two fold greater prevalence of major depressive disorder in women than in men. The reasons for the difference are hypothesized to involve hormonal differences, the effects of childbirth, differing psychosocial stressors for women and for men, and behavioral models of learned helplessness. In contrast to major depressive disorder, bipolar 1 disorder has an equal prevalence among men and women. Manic episodes are more common in men, and depressive episodes are more common in women. When manic episodes occur in women, they are more likely than men to present a mixed picture (e.g., mania and depression). Women also have a higher rate of being rapid cyclers, defined as having four or more manic episodes in a 1-year period.

Age
The onset of bipolar I disorder is earlier than that of major depressive disorder. The age of onset for bipolar I disorder ranges from childhood (as early as age 5 or 6) to 50 years or even older in rare cases, with a mean age of 30. The mean age of onset for major depressive disorder is about 40 years, with 50 percent of all patients having an onset between the ages of 20 and 50. Major depressive disorder can also begin in childhood or in old age. Recent epidemiological data suggest that the incidence of major depressive disorder may be increasing among people younger than 20 years of age. This may be related to the increased use of alcohol and drugs of abuse in this age group.

Marital Status
Major depressive disorder occurs most often in persons without close interpersonal relationships or in those who are divorced or separated. Bipolar I disorder is more common in divorced and single persons than among married persons, but this difference may reflect the early onset and the resulting marital discord characteristic of the disorder.

Socio economic and Cultural Factors
No correlation has been found between socioeconomic status and major depressive disorder. A higher than average incidence of bipolar I disorder is found among the upper socioeconomic groups. Bipolar 1 disorder is more common in persons who did not graduate from college than in college graduates, however, which may also reflect the relatively early age of onset for the disorder. Depression is more common in rural areas than in urban areas. The prevalence of mood disorder does not differ among races. A tendency exists, however, for examiners to under diagnose mood disorder and over diagnose schizophrenia in patients whose racial or cultural background differs from theirs.

Morbidity
Individuals with major mood disorders are at an increased risk of having one or more additional morbid Axis I disorders. The most frequent disorders are alcohol abuse or dependence, panic disorder, obsessive compulsive disorder (OCD), and social anxiety disorder. Conversely, individuals with substance use disorders and anxiety disorders also have an elevated risk of lifetime or current morbid mood disorder. In both unipolar and bipolar disorder, men more frequently present with substance use disorders, whereas women more frequently present with morbid anxiety and eating disorders. In general, patients who are bipolar more frequently show morbidity of substance use and anxiety disorders than do patients with unipolar major depression. In the Epidemiological Catchment Area (ECA) study, the lifetime history of substance use disorders, panic disorder, and OCD was approximately twice as high among patients with bipolar I disorder (61 percent, 21 percent, and 21 percent, respectively) than in patients with unipolar major depression (27 percent, 10 percent, and 12 percent, respectively). Morbid substance use disorders and anxiety disorders worsen the prognosis of the illness and markedly increase the risk of suicide among patients who are unipolar major depressive and bipolar.