The possibility of person specific identification of diagnosis in the NPR registry started in 2008.The non-ASD group consist of mostly typically developing children, though some children might have other diagnoses.Due to smaller sample size in the ASD female group, we did not include an interaction term between the severity score and diagnosis or sex (depending on analysis) in the subsequent logistic regression models.Including the interaction item introduced high collinearity between predictors for several item analyses leading to instability in parameter estimates.For example, the positive correlation between intellectual disability and severity of symptoms (Carter et al.), combined with the fact that males are more prone to developmental delay have led some to hypothesize that the higher prevalence of autism in males stems from a greater risk of developmental disability (Boyle et al. The exact nature of this relationship is unclear, and studies have found evidence that sex differences in cognitive performance, adaptive abilities and repetitive behaviors do not appear to be ASD specific, but instead bear a closer resemblance to those found in typically developing children (Messinger et al. However, other viewpoints stress specific biological factors related to autism, e.g.The present study uses the Mo Ba data release version 9, more about the sample selection displayed in Fig. It includes 23 yes-or-no questions to be completed by parents and followed-up by an interview with parents of children yielding a positive M-CHAT screen score.The M-CHAT was designed to be completed quickly in the waiting room of a primary care provider and has become one of the most frequently used screening instruments for ASD (Ibanez et al. In the present study, the M-CHAT checklist is used as an ASD-specific behavior measure in a large cohort, making it possible to examine early sex differences in children with or without ASD. Approximately 73 % of Mo Ba participants completed the 18-month questionnaire, which included the 23 items of the M-CHAT.
Both the Mo Ba and the ABC study obtained written informed consent from participating mothers and were approved by the Norwegian Data Inspectorate, as well as the Regional Committee for Medical and Health Research Ethics South-East Norway (REK).
The most frequently reported sex difference in ASD is the disproportionally higher male to female prevalence, consistently reported since the seminal studies by Kanner () reported across studies male to female prevalence ratios ranging from 4.3:1, with 5.5:1 in groups within the normal IQ range.
For moderate to severe intellectual disability male to female ratios of 1.33:1 (Mc Carthy et al. While numerous theories have been forwarded to explain the causal mechanisms of this predominantly high male–female ratio in ASD, the topic remains widely debated in the current literature.
In total, 40.6 % of invited mothers consented to participate.
The cohort comprises 114,500 children and 95,200 mothers.
) suggested ASD could be considered an extreme expression of normal male, compared to female, phenotypic profiles.