Everyone agrees there has been a remarkable increase in autism diagnosis across the world. There is, however, considerable debate about the reasons for this. Three very different kinds of explanation exist.
- Explanation #1 maintains that something in our modern environment has come along to increase the risk of autism. There are numerous candidates, as indicated in this blogpost by Emily Willingham.
- Explanation #2 sees the risks as largely biological or genetic, with changing patterns of reproduction altering prevalence rates, either because of assortative mating (not much evidence, in my view) or because of an increase in older parents (more plausible).
- Explanation #3 is very different: it says the increase is not a real increase – it’s just a change in what we count as autism. This has been termed ‘diagnostic substitution’ – the basic idea is that
children who would previously have received another diagnosis or no diagnosis are now being identified with autism spectrum disorder (ASD). This could be in part because of new conceptualisations of autism, but may also be fuelled by strategic considerations: resources for children with ASD tend to be much better than those for children with other related conditions, such as language impairment or intellectual handicaps, so this diagnosis may be preferred.