More research is necessary
Basically, it appears that autism spectrum disorder isn't rampantly rising in prevalence as previous studies may have found. However, there may be some reasons as to why the National Health Interview Survey may have found different prevalence trends than previous reports. In the previous reports, the prevalence was measured only at particular institutions or localized areas. The National Health interview Survey took the next step to evaluate trends at a national level. Additionally, the survey in this study used parent reporting to gauge physician diagnoses of autism spectrum disorder. Though we can say this is relatively reliable, it's not nearly as foolproof as documented information. In previous reports, clinical reviews of education or healthcare evaluations were used to gauge how many children actually had the disorder. This may actually be a little more accurate than conducting a survey of families.