In order to diagnose or understand ASD, there need to be comparisons to other groups of people and the peers of the child with autism. There might be a difference in the mental age of the child compared to their chronological age, which can only be seen through comparisons. Does the child have a delay in reaching developmental milestones that their peers reached? Are their developmental milestones more in line with that of a different chronological age group, or do they have altered responses in behavior than expected to people of the same mental age?

A child with autism might be able to explain and understand where emotions come from without being able to reflect or understand the emotions themselves. This is an altered response.