mation from several informants: mothers, fathers, teachers, and children themselves. Each informant brings a unique view of the child, so the number and nature of informants affect the prevalence estimate.
Missing from both Table 2-2 and Figure 2-1 are some rare but often severe disorders; for example, schizophrenia, bipolar disorder, and pervasive developmental disorders. The reason is that studies to date have not been large or numerous enough to capture these rare disorders with any hope of accuracy. For example, the two studies that included schizophrenia had rates of 6 per 1,000 and 7 per 1,000, respectively (Wittchen, Essau, et al., 1992; Costello, Angold, et al., 1996). The three available estimates for adolescent bipolar disorder (two from the same study) fell between 1 and 3 per 1,000 (Lewinsohn, Rohde, et al., 1998; Costello, Angold, et al., 1996), although prevalence increases in young adulthood (Wittchen, Nelson, and Lachner, 1998). No population-based estimates are available for prepubertal bipolar disorder.
Despite the variability across studies, it is possible to draw some general observations about prevalence. The mean (17 percent) and median (17.5 percent) estimates for one or more MEB disorders were very close, with 50 percent of studies producing estimates between 12 and 22 percent, suggesting that this estimate is fairly reliable. The rank ordering of prevalence estimates for the different disorders was remarkably consistent across the individual studies. Of the diagnoses included in Figure 2-1, the lowest prevalence rates came from studies of younger children, especially those from Scandinavia, while the highest rates were reported from studies of young adults (ages 19-24). However, from the point of view of prevention, it should be noted that a review of studies of preschool children concluded that almost 20 percent of 2- to 5-year-olds had at least one DSM-IV disorder in the past three months (Egger and Angold, 2006), the same rate as seen in older children, adolescents, and young adults.
Within studies, after controlling for risk exposures that are often confounded with race/ethnicity, such as poverty (Costello, Compton, et al., 2003), parental incarceration (Phillips, Erkanli, et al., 2006), or migrant status (Bengi-Arslan, Verhulst, et al., 1997), similarities across different racial/ethnic groups are much more noticeable than are differences (Costello, Keeler, and Angold, 2001; Loeber, Farrington, et al., 2003). Disruptive behavior disorders (conduct disorder, oppositional defiant disorder), ADHD (Rutter, Caspi, and Moffitt, 2003), and substance use disorders (Wittchen, Nelson, and Lachner, 1998) tend to be more common in boys than girls, while the opposite is true of emotional disorders (depression, anxiety disorders). About half of the children with a diagnosis have a disorder that causes significant functional impairment—that is, a disorder that impedes their ability to function and develop appropriately in human