> I learned the opposite, that the term spectrum is used when it is not same problem to different degrees. That's how the autism spectrum was explained to me, because the problem differs over the spectrum.
The autism spectrum, in specific, was unified from what had been listed as separate disorders. That was done because the view was reached that these disorders reflected different degrees of the same underlying problem.
> That was done because the view was reached that these disorders reflected different degrees of the same underlying problem.
No, precisely the opposite. They weren't different degrees of the same underlying problem, they were a few different combinations of symptoms from a few different symptom categories: social, communication, and repetitive behaviors.
Something being a spectrum is not just a matter of intensity on a single axis ("more or less autistic"). Imagine a graph of the visible light spectrum, wavelengths map to symptoms and their intensities map to symptom severities.
ASD is a spectrum because different individuals have different levels of impairment in each area.
Consider this: Why is ASD a spectrum disorder and social anxiety isn't? Surely you don't believe that anxiety only comes in a single level of severity.
The autism spectrum, in specific, was unified from what had been listed as separate disorders. That was done because the view was reached that these disorders reflected different degrees of the same underlying problem.