A recent study in Nova Scotia, Canada, suggested that several factors affect the age at diagnosis of autism spectrum disorders (ASD).15 Suppose an additional study was conducted to determine whether...

A recent study in Nova Scotia, Canada, suggested that several factors affect the age at diagnosis of autism spectrum disorders (ASD).15 Suppose an additional study was conducted to determine whether age at ASD diagnosis is affected by county and a diagnosis of attention-deficit hyperactivity disorder (ADHD). A random sample of newly diagnosed ASD children was obtained for each combination of county and ADHD diagnosis (1 = no; 2 = yes), and the age of each child was recorded.