Trinity Kubassek/Pexels
Source: Trinity Kubassek/Pexels

Childhood mental illness is far from rare, as we noted in a previous post. In fact, most children—three in five—will have been diagnosed with a mental disorder by the time they reach adulthood. Paradoxically, while most children experience mental illness at some point in development, relatively few are ill at any given moment.  Something common can thus appear to be rare, and that misperception contributes to the stigma surrounding mental illness.

Even this picture is incomplete, however.

Most studies that count children with mental illness focus on those who meet full criteria for a psychiatric disorder. On first glance, this approach seems to make sense. Yet by excluding those who fall just below a somewhat arbitrary diagnostic cutoff, such tallies may omit many children with emotional or behavioral problems that impair their ability make friends or to be successful at home and school.

Let me give you an example. To meet full diagnostic criteria for attention-deficit/hyperactivity disorder, a child must display at least six of nine inattention symptoms or six of nine hyperactive-impulsive symptoms. This seems straightforward enough. However, it is possible for a child to have four or five symptoms of inattention and four or five symptoms of hyperactivity/impulsivity (or eight to 10 symptoms in total) and still not meet criteria for ADHD. In fact an undiagnosed child may have more symptoms than another child who is diagnosed with a mental disorder.

It is reasonable to wonder whether this make sense. Certainly, our goal is not to diagnose all children with mild symptoms. Yet children who don’t meet standard diagnostic cutoffs may be just as impaired or in just as much distress as children who do. In his paper Impaired but Undiagnosed, Dr. Adrian Angold showed that children with subclinical but impairing problems are at risk to meet full criteria for a disorder in the future. Regardless of how want to classify them, many children in this sub-threshold category require help and intervention.

This is not a trivial concern. Studies suggest that between 10 and 15 percent of children are impaired but undiagnosed, meaning that for every child with a mental disorder, another child goes undiagnosed but struggles with emotional or behavioral problems all the same (Angold, Costello, Farmer, Burns, & Erkanli, 1999; Lewinsohn, Shankman, Gau, & Klein, 2004; Roberts, Fisher, Turner, & Tang, 2015).

We noted that approximately three in five children will have met full criteria for a psychiatric disorder by adulthood. If we include undiagnosed but impaired children, that number grows significantly: When both groups are counted, well over 80 percent of children experience some sort of impairing psychiatric problem by adulthood (Copeland, Shanahan, Costello, & Angold, 2011). This suggests that the experience of psychiatric illness in childhood is not only common, but nearly universal. In other words, children who meet full criteria for a psychiatric disorder represent the mere tip of the iceberg that is childhood mental illness.

Could it actually be the case the almost all children experience mental illness? This concept may not be as radical as it initially sounds. First of all, the umbrella of mental illness includes rare conditions such as bipolar disorder, but also common conditions, such as substance abuse or depression.

It’s also useful to compare childhood experiences of mental and physical illness. Indisputably, all children experience physical illness many times by the time they reach adulthood. Not all of those physical illnesses are chronic and severe. Rather, physical illness exists on continuum, with a limited number of life-threatening conditions on one end and a large number of less severe, albeit impairing, conditions on the other.  Because they are so common, these less severe conditions typically account for the greatest costs to society in terms of sick days, productivity losses and impairment in daily living.

The data strongly suggests that mental illness is no different: It is a nearly universal experience marked by different grades of severity and impairment. If this was better understood, then perhaps popular notions of mental illness might begin to shift as well. Perhaps the stigma that shrouds mental illness would be replaced with a broad acceptance that mental illness, like physical illness, is simply part of the human experience.

Once one recognizes the wide reach of childhood mental illness, another question quickly suggests itself: Who gets help? We’ll take a look at that issue in an upcoming post.


Angold, A., Costello, E. J., Farmer, E. M. Z., Burns, B. J., & Erkanli, A. (1999). Impaired but undiagnosed. Journal of the American Academy of Child and Adolescent Psychiatry, 38, 129-137.

Copeland, W., Shanahan, L., Costello, E. J., & Angold, A. (2011). Cumulative Prevalence of Psychiatric Disorders by Young Adulthood: A Prospective Cohort Analysis From the Great Smoky Mountains Study. Journal of the American Academy of Child & Adolescent Psychiatry, 50(3), 252-261. doi: DOI: 10.1016/j.jaac.2010.12.014

Lewinsohn, P. M., Shankman, S. A., Gau, J. M., & Klein, D. N. (2004). The prevalence of comorbidity of subthreshold psychiatric conditions. Psychological Medicine, 34, 613-622. 

About the Author

E. Jane Costello, Ph.D. and William E. Copeland, Ph.D.

E. Jane Costello and William Copeland work in the Department of Psychiatry and Behavioral Sciences at Duke University.

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