Individuals with<unk>  meet the DSM-5 classification criteria for both MDD and PDD. Goldney and Fisher (2004) determined that, in a sample of 3,010 individuals from southern portions of Australia calculated a prevalence rate of<unk>  of 2.2%. Jonas et al. (2003) reported a prevalence rate of<unk>  in the United States of 3.4%—based upon an assessment of 7,667 Americans. The prevalence rate of<unk>  can be compared to rates of PDD at 6.2%, major depressive episode (MDE) at 8.6%, and major depressive episode with severity (MDE-s) at 7.7%. Keller and Shapiro (1982) found that 26% of patients within a sample of 101 met the criteria for both MDD and PDD; however, the aforementioned sample is much smaller—and much more inclined to inaccuracies—than the samples (3,010 and 7,667) described above. Thus,<unk>  is less common than other forms of depression, but it is still a form of depression that warrants medical attention in the form of behavioral therapies; pharmaceutical treatments; or, both (Miller, Norman, and Keitner, 1999). The characteristics of those with<unk>  tend to be more severe in nature than those associated with those who have either MDD or PDD. Levitt, Joffe, and MacDonald (1991) found that those with<unk>  experience fluctuations in mood at an earlier point in life, a more substantial number of depressive episodes, as well as co-morbid disorders of anxieties more often than their MDD-alone counterparts. Goldney and Fisher (2004) reported that individuals with<unk>  seek medical attention more often than those with either MDD or PDD alone. Leader and Klein (1996) found that individuals with<unk>  experience a more substantial level of social impairment, which includes factors such as leisure pursuits and relationship characteristics, than those with either MDD or PDD. Dixon and Thyer (1998) concluded that individuals with<unk>  experiences recoveries on a more frequent basis than their counterparts who have MDD alone (88% to 69%); however, individuals with<unk>  experience the most substantial rates of relapse of all of those who suffer from chronic depression. In addition, remission from MDD tends to happen faster than remission from PDD (Dixon & Thyer, 1998). Miller, Norman, and Dow (1986) reported that individuals with<unk>  endure a more severe path of illness, but experience few differences with respect to social impairment compared to their MDD-alone counterparts. In addition, McCullough et al. (2000) found that, with the exception that patients with<unk>  tended to experience of more severe illness, few differences were apparent. Therefore, the conclusions drawn in previous research that are associated with the nature of the clinical presentation of<unk>  are mixed. Multiple scientists emphasize the need for additional research to determine adequate treatments for those with<unk> , as depression is a disease that places a considerable burden upon communities and societies; furthermore, those researchers predict depression will be, in an economic sense, the second-most burdensome disease on societies come 2020.
Double depression
Long-term depression
Retarded depression
Outline of bipolar disorder
Treatment-resistant depression
Depression 
Late life depression
Recurrent brief depression