Several comparisons are notable. First, diagnosed cases of DSM-III-R MDD from our epidemiological survey are phenomenologically very similar to clinical cases of MDD in treatment settings. With two exceptions, prevalence rates of DSM-III-R symptoms in the OADP sample fall within the range of the six patient samples. The exceptions are weight/appetite disturbance and sleep difficulties, which were more often reported by the OADP participants. Another trend was for community subjects to report fewer thoughts of death and/or suicidal tendencies than their clinical counterparts, albeit the 55% prevalence rate is well within the range of 49% to 92% in the clinical samples.
Age Differences in Symptom Presentation
Given that the community cases of MDD appeared comparable to clinic cases, we examined whether the phenomenology of MDD changes during childhood and adolescence. To accomplish this, symptom prevalence values were compared in MDD episodes that occurred before age 14 (n = 100) with episodes that occurred after age 14 (n = 292). None of the differences in symptom prevalence for the two age groups were significant.
A more important test of the age question would be to compare the symptom prevalence rates for MDD in adult samples. The pattern of symptoms in our depressed adolescents is generally similar to results from depressed adults identified in the Epidemiologic Catchment Area study. Depressed adolescents were more likely to report worthlessness/guilt than depressed adults and were less likely to report weight/appetite changes and thoughts of death or suicide. Overall, these findings suggest that there are relatively few differences in the MDD phenomenology for adults and younger and older adolescents.
Gender Differences in Symptom Presentation
The next question we addressed was whether patterns of MDD symptoms in girls and boys differ. Among OADP participants with MDD (269 girls and 123 boys), prevalence rates of two of the nine symptoms were significantly different. Compared to depressed boys, depressed girls more often reported weight/appetite disturbance (77.0% vs. 58.5%) and worthlessness/guilt (82.5% vs. 67.5%). These differences may indicate a slightly different focus for treatment of depressed adolescent girls versus boys. Among the non-cases, MDD symptom rates in girls were consistently higher than for boys, but the two patterns are quite similar and none of the gender differences were statistically significant.
Epidemiology of depression
Data from the OADP provide estimates of the basic parameters of MDD epidemiology including point prevalence (i.e., percentage in an episode of MDD at a given point in time), lifetime prevalence (i.e., percentage who have experienced an MDD episode during their lifetime), and incidence (i.e., percentage who are not depressed at the beginning of an observation period who develop an MDD episode during a specified period of time; in our case, 1 year). Incidence rates are customarily divided into first incidence (i.e., percentage who develop an MDD episode for the first time during the incidence interval) and recurrence (i.e., percentage with a previous episode of MDD who developed another episode during the interval). From a public health perspective, the total incidence rate is important for planning the delivery of mental health services in that it indicates how many individuals in the population will become depressed during a certain time period. Epidemiologic data from the OADP are shown in Table 3.