(Note: This post summarizes content found in my new book Child Temperament: New Thinking About the Boundary Between Traits and Disorders. If you like what you read, I urge you to find out more)
Blood pressure is not a disease. All of us have one and the numbers, if measured across a large sample of people, fall into one of those classic bell-shaped curves. At a pressure above 140/90, however, that characteristic becomes an illness and worthy of treatment with remedies ranging from a low-salt diet to prescription medications.
Modern psychiatry, however, has resisted such a conceptualization of its conditions, opting instead for more of an all-or-none model in which a person either does or does not have a psychiatric illness. Our temperament or personality traits, it follows, don’t have much to do with these disorders. Happy people can get depressed, and fearless people can develop anxiety disorders.
Certainly there are many cases where such presentations are true, but are the worlds of personality and psychopathology really that distinct? Accumulating research studies are consistently saying that they are not, and that many if not most disorders exist not in a binary yes-no form but as more of a spectrum or continuum, not unlike blood pressure. The relation between a child’s activity level or attentional abilities and the diagnosis ADHD is likely one of the best examples of this phenomenon. Moreover, there is good reason to suspect that the “speed limit” between what is considered a normal and abnormal level of behavior has been dropping over the past several decades from everything from ADHD to autism to bipolar disorder. This shift is likely responsible for at least some of the “epidemic” rates of psychiatric disorders observed today, despite other evidence that the overall level of problem behavior in children has remained fairly constant.