Epidemiologic data from large community surveys in the United States on the incidence of MDD among children and adolescents are sparse. This is in part due to the long-held view that MDD was rare before adulthood or was a self-limiting and normal part of growing up. In

addition, there has been controversy over the means of assessing young people and over who is the best informant, the child or the parent. A few surveys of adolescents have used self-report depression symptom scales assessing 1 week to 6 months prevalence. Rates based on established adult cutoff scores for clinically significant current depression range between 20% and 30% (Offord et al., 1987; Reinherz, Giaconia, Hauf, Wasserman, & Silverman, 1999; Wickstrom, 1999). However, self-reported symptom scales do not differentiate between mild and severe mood disorders, type of mood disorder, or other psychiatric disorders. Prevalence rates with self-report scales are generally considerably higher than those found in studies using diagnostic assessments.

Published epidemiologic studies of adolescents have been limited to school districts and high schools in one community (Lewinsohn, Hops, Roberts, Seeley, & Andrews, 1993; Whittaker et al., 1990) or limited geographic areas (Cohen et al., 1993; Costello et al., 1996), or have been conducted outside the United States in Canada (Flemming, Offord, & Boyle, 1989) or New Zealand (Fergusson & Woodward, 2002). With few exceptions (Flemming et al., 1989; Lewinsohn, Hops, et al., 1993); the samples of adolescents have usually been too small, under 1,000 and usually under 500, to be reliable estimates. The diagnostic methods and age groups of the adolescents vary widely among studies. The current lifetime prevalence rates of MDD from these studies have been estimated to be about 5%. The similarity between lifetime rates in adolescents and adults suggests that a large percentage of those with major depression have onset while young.

The most comprehensive epidemiologic data in adults come from the National Comorbidity Survey (NCS; Kessler & Walters 1998), a nationally representative sample of over 8,000 persons from U.S. households ages 15 to 54 (Kessler & Walters, 1998). Although only 600 persons under age 18 were included in this sample, the rates from this U.S. population are consistent with published rates on adolescents. The lifetime prevalence for 15-to 18-year-olds was about 14% and an additional 11% were estimated to have a lifetime history of minor depression, with higher rates among females than among males. While the NCS did not sample persons under age 15, the sample was young enough so that reasonably good information from retrospective reports of age of first onset of MDD in childhood or adolescence could be obtained. Kaplan-Meier age-at-onset curves for major and minor depression in the NCS are presented in Figures 1.1 (major depression) and 1.2 (minor depression). Both curves show that meaningful risk begins in the early teens and continues to rise in a roughly linear fashion within groups of cohorts through the mid-20s (Kessler, Avenevoli, & Merikangas, 2001). The general shape of these curves is very similar to that of the onset curves reported in other epidemiologic studies of adolescent depression (e.g., Lewinsohn et al., 1998). The peak rise in rates in the late teens and early 20s is also consistent with the mean age of onset reported in the cross-national studies of adults (Weissman et al., 1996). Both curves show evidence of substantial prevalence increases in cohorts born af

ter the mid-1960s. A cohort effect (that is, secular changes in rates) has also been shown in cross-national epidemiologic studies of adults, spanning a considerable older age range (Cross-National Collaborative Group, 1992; Klerman & Weissman, 1989). These statistics need to be reconciled with data derived from clinical samples documenting that more than 30% of children referred to clinical centers suffer from major depression and that in many of these cases, the disorder starts in the preschool years. Moreover, recent reports from student health services on college campuses note a marked increase in requests for counseling for depression over the last decade and list suicide as the second leading cause of death among students (Voelker, 2003). In summary, there is good evidence that the first onset of MDD is frequently in adolescence and not uncommonly in childhood, and that the rates of MDD, especially in the young, have been increasing.