A Major Depressive Episode (MDE) is defined as a period of at least 2 weeks when a person experiences a depressed mood or loss of interest or pleasure in daily activities, plus at least four additional symptoms of depression (such as problems with sleep, eating, energy, concentration, and feelings of self-worth) (American Psychiatric Association 1994). In 2009, about 14 percent of 14- to 25-year-olds reported having had an MDE in their lifetime, which was not measurably different from the percentage in 2006. From 2006 to 2009, the percentages of males and females who had experienced an MDE did not measurably change; nor were there differences from 2006 to 2009 among 14- to 17-year-olds and 18- to 20-year-olds. However, among all 21- to 25-year-olds, the percentage who reported having an MDE in their lifetime decreased from 16 to 14 percent, and the percentage among females in this age group decreased from 20 to 18 percent. In contrast, the percentage of male 14- to 17-year-olds reporting an MDE increased from 8 percent in 2006 to 10 percent in 2009. Among 14- to 25-year-olds, higher percentages of females than males reported having experienced an MDE in their lifetime in each year from 2006 through 2009; in 2009, the reported incidence of lifetime MDEs was about twice as high for females as for males (19 vs. 10 percent). Differences also emerged when examining reports of lifetime MDEs by age group. The percentage of reported lifetime MDEs in 2009 for 14- to 17-year-olds (15 percent) was higher than the percentage for 18- to 20-year-olds (13 percent).
In 2009, higher percentages of 14- to 17-year-olds (10 percent) reported having an MDE in the past year than did 18- to 20-year-olds and 21- to 25-year-olds (8 percent each). Across all three age groups, higher percentages of females than males reported having an MDE in the past year. For example, 11 percent of female 18- to 20-year-olds reported having an MDE in the past year, compared with 5 percent of male 18- to 20-year-olds.