Ferris Jabr writes at Scientific American:
What is in question is how many of the DSM-5 criteria a patient must meet to receive a diagnosis—too many and the manual excludes autistic people with fewer or milder symptoms; too few and it assigns autism to people who don't have it. Since the 1980s the prevalence of autism has dramatically increased worldwide, especially in the U.S. where the Centers for Disease Control and Prevention estimates that nine per 1,000 children have been diagnosed with ASD. Many psychiatrists agree that the increase is at least partially explained by loose criteria in DSM-IV.
"If the DSM-IV criteria are taken too literally, anybody in the world could qualify for Asperger's or PDD-NOS," says Catherine Lord, one of the members of the APA's DSM-5 Development Neurodevelopmental Disorders Work Group. "The specificity is terrible. We need to make sure the criteria are not pulling in kids who do not have these disorders."
Three studies published between last summer and this month conclude that the DSM-5 criteria for ASD are too strict, but that a few small changes would make them appropriately inclusive. One might think that the APA would conduct such research themselves, but studies that explicitly compare DSM-IV and DSM-5 criteria are not an official part of the revision process. Rather, researchers who are not helping revamp the DSM, but were interested in how the new edition will change psychiatric diagnosis, decided to find out for themselves.In a sidebar, Jabr runs the numbers:
[W]e asked astronomer and Hubble Fellow Joshua Peek of Columbia University to code a computer program that would calculate the total possible ways to get a diagnosis of autistic disorder in DSM-IV and the total possible ways to get a diagnosis of autism spectrum disorder in DSM-5. You can do the math by hand too, if you like: It all comes down to factorials. The DSM-IV criteria are a set of 12 items in three groups from which you must choose 6, with at least two items from group one and at least one item each from groups two and three. The DSM-5 criteria are a set of 7 items in two groups from which you must choose 5, including all three items in group one and at least two of the four items in group two. Peek's program crunched the numbers: there are 2027 different ways to be diagnosed with autism in DSM-IV and 11 ways to be diagnosed with autism in DSM-5.
One might think that those statistics make it absurdly easy to qualify for a diagnosis of autism in DSM-IV and incredibly difficult to meet the criteria for autism in DSM-5, but those numbers alone don't tell you anything unless you understand how common each symptom of autism is in the general population. Symptoms of autism are not randomly distributed throughout the population and the symptoms do not cluster together in random combinations. Research in the past decade has shown that some symptoms appear together much more often than others. In fact, that is one of the main reasons that the APA has consolidated the DSM-IV criteria for autism into fewer, denser and more accurate criteria in the DSM-5. The idea is that the DSM-IV criteria allowed for too many possible combinations, many of which rarely occur; the DSM-5 criteria, in contrast, better reflect the most common combinations of symptoms.