The American Psychiatric Association have just published the latest update of the draft DSM-5 psychiatric diagnosis manual, which is due to be completed in 2013. The changes have provoked much comment, criticism, and heated debate, and many have used the opportunity to attack psychiatric diagnosis and the perceived failure to find “biological tests” to replace descriptions of mental phenomena. But to understand the strengths and weaknesses of psychiatric diagnosis, it’s important to know where the challenges lie.
Think of classifying mental illness like classifying literature. For the purposes of research and for the purposes of helping people with their reading, I want to be able to say whether a book falls within a certain genre—perhaps supernatural horror, romantic fiction, or historical biography. The problem is similar because both mental disorder and literature are largely defined at the level of meaning, which inevitably involves our subjective perceptions. For example, there is no objective way of defining whether a book is a love story or whether a person has a low mood. This fact is used by some to suggest that the diagnosis of mental illness is just “made up” or “purely subjective,” but this is clearly rubbish. Although the experience is partly subjective, we can often agree on classifications.
Speaking the same language
How well people can agree on a classification is known as inter-rater reliability and to have a diagnosis accepted, you should ideally demonstrate that different people can use the same definition to classify different cases in the same way. In other words, we want to be sure that we’re all speaking the same language—when one doctor says a patient has “depression,” another should agree. To do this, it’s important to have definitions that are easy to interpret and apply, and that rely on widely recognised features.
To return to our literature example, it’s possible to define romantic fiction in different ways, but if I want to make sure that other people can use my definition it’s important to choose criteria that are clear, concise, and easily applicable. It’s easier to decide whether the book has “a romantic relationship between two of the main characters” than whether the book involves “an exploration of love, loss and the yearning of the heart.” Similarly, “low mood” is easier to detect than a “melancholic temperament.”