The lay summary:
Public policy toward autistic people is driven by data. Most autism data to date have been derived from and about children, because autism tends to be identified and supported in the public school system. This has created a public perception of autism as a childhood problem. In fact, autism is a lifelong difference or disability, and recent studies suggest serious overlooked concerns for autistic adults. This commentary discusses how we have evaluated adult autism so far, limitations of our knowledge, and how we might evaluate adult needs going forward. The commentary makes a case for specific new adult prevalence and outcome studies to inform public policy.From the article:
When discussing autism in public policy our first question might be how many adults are actually at risk? The fact is, we do not know the size of our adult autistic population, and we do not know if the outcome data we have is broadly applicable, or only applies to the subset profiled by the studies. The arguments that it does not apply are just as strong as those that it does.
Amazingly, there is only one large‐scale study measuring adult prevalence. In 2011, Terry Brugha of the University of Leicester evaluated autism prevalence in a British community [Brugha et al., 2011]. That project was based on a survey of 7461 adults and looked at rates of autism and social attainment. Perhaps the most significant finding was that the rate of autism was not age‐dependent, but the rate of existing diagnosis was. Brugha et al.  found a fairly constant prevalence independent of year of birth. The older the study participant, the less likely they were to have been previously diagnosed with autism.
The finding that most older adults were not originally diagnosed with autism is consistent with anecdotal accounts of older autistic people ...If those and the Brugha et al.  data are a guide, there are many older autistic adults who are unaware they would be on the autism spectrum if evaluated today. Brugha et al.  found very high rates of autism among older adults previously diagnosed with learning disabilities, and they found a large number of autistic people living in group or institutional settings. Neither of those findings are surprising.
According to Brugha et al. , with our current best estimates of prevalence, roughly one in 50 men, or one in 75 people of all ages are on the autism spectrum.
Adult outcomes range from institutionalization to invisibly blending into the community, yielding a colossal range of implications for supports and services. If we are to have an informed autism policy, we need accurate data characterizing autistic adults. What studies like Croen et al.  show is that the diagnosed (and therefore identifiable) older adult autistic population has an alarming set of problems, but Brugha and other findings suggest they are only a small percentage of the actual adult population. We do not know anything of the health of the rest. To accurately survey the medical issues of all autistic adults, we must identify a broad enough swath to describe the population. That probably means conducting a larger scale study like Brugha et al.  in the U.S.
- Brugha, T. S., McManus, S., Bankart, J., Scott, F., Purdon, S., Smith, J., … Meltzer, H. ( 2011).Epidemiology of autism spectrum disorders in adults in the community of England. JAMA Psychiatry, 68( 5), 459– 465. https://doi-org.ccl.idm.oclc.org/10.1001/archgenpsychiatry. Google ScholarFull Text
- Croen, L. A., Zerbo, O., Qian, Y., Massolo, M. L., Rich, S., Sidney, S., & Kripke, C. ( 2015). The health status of adults on the autism spectrum. Autism, 19( 7), 814– 823. https://doi-org.ccl.idm.oclc.org/10.1177/1362361315577517.CrossrefPubMedWeb of Science®Google ScholarFull Text