|Old man @ Wikipedia|
In these days of calls for ever earlier identification, diagnosis and intervention where autism is concerned, it is still a stark reality for many that autism [in childhood] is diagnosed at a much later point from where initial concerns were raised/detected. Of course, one has to take into account issues around the plurality of autism (see here) and that there may be stability issues with the early days of some autism presentation (see here). But still diagnosis can be a long and drawn out process; sometimes even adversely influenced by the views and opinions of clinicians themselves (see here) despite there being some [very] NICE guidance available, at least for parts of the UK.
During the early years of my research career I remember my go-to study on the topic of age at autism diagnosis was the report by Howlin & Asgharian  and their findings: "In the 'autism group' the average age when diagnosis was confirmed was around 5.5 years; in the 'Asperger group' it was 11 years" based on a UK-based sample of nearly 800 families in the late 1990s. Unfortunately, even in the following years, things seem to have got only marginally better when it comes to age at diagnosis as per the report by Mandell and colleagues  (64.9 months for all ASDs) and indeed, some of our own data . The latest CDC estimates of autism in the US (see here) reported by Wingate and colleagues  does however hint that things might be continuing to move in the right direction as per their findings: "Although ASD is sometimes diagnosed by 2 years of age, the median age of the first ASD diagnosis remains older than age 4 years in the ADDM Network communities". This bearing in mind the different geographical locations of these studies and different processes in place leading up to diagnostic assessment.
To the question then of what factors might influence age of diagnosis outside of just resource issues (similar to the diagnosis of autism in adults), there are some clues from the collected literature which I'm gonna cherry pick. Bear in mind though, that there is no one-size-fits-all formula when it comes to answering this important question.
- Daniels & Mandell  surveyed some of the collected literature in this area. Perhaps unsurprisingly "greater symptom severity" was one of the core factors associated with earlier diagnosis. Some of this authorship group have gone into further detail about which symptoms might affect age and diagnosis . On that occasion they concluded that: "Children with severe language deficits received a diagnosis an average of 1.2 years earlier than other children. Hand flapping, toe walking, and sustained odd play were associated with a decrease in the age of diagnosis, whereas oversensitivity to pain and hearing impairment were associated with an increase".
- Frenette and colleagues  in their study reported that: "a one year increase in maternal age at delivery was associated with a 0.06 decrease in age at ASD diagnosis". So there might be something of a correlation between older mums and earlier diagnosis. This suggests one or more factors might pertain: (a) older mums with more 'life experience' and perhaps with a greater likelihood of having other children, might be more sensitive to symptoms, or (b) younger mums with less 'life experience' might be less sensitive to symptoms. Right or wrong, that's my interpretation anyway, and certainly, it was something noted by Fountain and colleagues  (open-access here).
- The paper by Rosenberg and colleagues  (open-access here) did not find any one factor as being linked to age at diagnosis. That being said they did suggest that: "Both ID [intellectual disability] and history of autistic regression were associated with earlier AOD [age of initial diagnosis]". They similarly noted the differences in age at diagnosis between different diagnoses on the autism spectrum. Race and gender was also picked up.
- Ethnicity was also something picked up in the study by Coo and colleagues  (open-access here). They noted that: "rural residence, diagnosis in more recent years, and foreign birthplace were associated with a later age at diagnosis". They continue: "Children who are visible minorities or who have siblings with ASD were more likely to be diagnosed earlier". Not everyone however agrees with those sentiments as per the paper by Valicenti-McDermott and colleagues .
I think what we can take from this collected data is that there are many influences pushing and pulling at the age of diagnosis of autism outside of the levels of resources available and other population factors. Presentation of symptoms in terms of timing and severity are the obvious factors which seem to influence age at diagnosis. Regression in symptoms, as I've talked about a few times on this blog (see here and see here) probably depends on how severe the regression was and when it happened.
Outside of the continued need for early and accurate diagnosis, there are other important implications from any change in age at diagnosis. So for example, the potential to affect autism prevalence estimates as per the conclusions by Parner and colleagues  is something to consider. Whether also early diagnosis and by assumption, early intervention might also have some important effects on say, the likelihood of joining that optimal outcome group (see here) is another consideration too.
Music to close. Please do not mention the football. Or as someone noted for fans of the England football (soccer) team "that familiar sense of utter disappointment. Hello old friend". So instead a 'sit back and enjoy the summer' song: Waves.
 Mishaal RA. et al. Age of autism spectrum disorder diagnosis is associated with child's variables and parental experience. Res Autism Spect Disord. 2014; 8: 873-880.
 Howlin P. & Asgharian A. The diagnosis of autism and Asperger syndrome: findings from a survey of 770 families. Dev Med Child Neurol. 1999 Dec;41(12):834-9.
 Mandell DS. et al. Age of diagnosis among Medicaid-enrolled children with autism, 2001-2004. Psychiatr Serv. 2010 Aug;61(8):822-9.
 Whiteley P. et al. Trends in Developmental, Behavioral and Somatic Factors by Diagnostic Sub-group in Pervasive Developmental Disorders: A Follow-up Analysis. Autism Insights. 2009; 1: 3-17.
 Wingate M. et al. Prevalence of autism spectrum disorder among children aged 8 years - autism and developmental disabilities monitoring network, 11 sites, United States, 2010. MMWR Surveill Summ. 2014 Mar 28;63(2):1-21.
 Daniels AM. & Mandell DS. Explaining differences in age at autism spectrum disorder diagnosis: A critical review. Autism. 2013 Jun 20.
 Mandell DS. et al. Factors associated with age of diagnosis among children with autism spectrum disorders. Pediatrics. 2005 Dec;116(6):1480-6.
 Frenette P. et al. Factors affecting the age at diagnosis of autism spectrum disorders in Nova Scotia, Canada. Autism. 2013 Mar;17(2):184-95.
 Fountain C. et al. Age of diagnosis for autism: individual and community factors across 10 birth cohorts. J Epidemiol Community Health. 2011 Jun;65(6):503-10.
 Rosenberg RE. et al. Factors affecting age at initial autism spectrum disorder diagnosis in a national survey. Autism Res Treat. 2011;2011:874619.
 Coo H. et al. Correlates of age at diagnosis of autism spectrum disorders in six Canadian regions. Chronic Dis Inj Can. 2012 Mar;32(2):90-100.
 Valicenti-McDermott M. et al. Age at diagnosis of autism spectrum disorders. J Pediatr. 2012 Sep;161(3):554-6.
 Parner ET. et al. Autism prevalence trends over time in Denmark: changes in prevalence and age at diagnosis. Arch Pediatr Adolesc Med. 2008 Dec;162(12):1150-6.
Mishaal, R., Ben-Itzchak, E., & Zachor, D. (2014). Age of autism spectrum disorder diagnosis is associated with child's variables and parental experience Research in Autism Spectrum Disorders, 8 (7), 873-880 DOI: 10.1016/j.rasd.2014.04.001