Lifetime prevalence (LTP) is a statistic that describes the number of people within a population who can be expected to develop a disorder at some point in their lives. For Major Depression, estimates of the LTP in diverse community studies vary between 10% to 25% in women and 5% to 12% in men. These figures suggest that Major Depression is very common. Approximately 1 in 5 women, and up to 1 in 10 men may become depressed at some point in their lives!

Major depression can occur during a wide range of ages. However, the average age of onset for depression is the mid-20s. Developing MDD does not seem to be related to someone's level of education, income, or marital status. Although both men and women can experience depression, it is more common in women, probably because hormones associated with the menstrual cycle and the postpartum period can wreak havoc on mood (See information below on PMDD and the postpartum specifier).

For some people, depressive symptoms become so severe and intense that they attempt or actually commit suicide. Research has shown that more than 90% of people who kill themselves have depression or another diagnosable mental illness or substance abuse disorder. However, statistics summarizing completed suicides fail to capture the true scope of this problem; for every suicide death there are estimated to be between 8 and 25 attempted suicides. Obviously, suicide risk is heightened during Major Depression. We will discuss more about suicide at the end of this paper.