The study's point isn't to measure the prevalence or increase of autism diagnosis among a population--they are doing a simple study comparing diagnoses of children with fat parents, and diagnoses of children with nonfat parents. Increase or prevalence of autism isn't what the study is about, although yes-- diagnosis has increased as the symptoms have become a broader catch all in the DSM whatever. But again, not the point. The interesting thing here is that BMI of the mother had less of a correlation than BMI of the father. Obese men were almost twice as likely to produce autistic offspring as normal bmi men. This is notable, because up until recently, men were entirely off the hook for offspring abnormalities, and women were always blamed for being too old, or unhealthy, or whatever. We are recently finding that men's sperm health is an absolute contributing factor to offspring health and I appreciate them adding to the conversation.