A validity analysis of selected instruments used to assess autism.

The team compared three autism checklists. They wanted to know which one best tells autism apart from severe intellectual disability. Kids with autism and kids with severe ID completed the CARS, ASIEP, and one other tool.

CARS and ASIEP gave the cleanest split. All three tools separated the groups, but CARS and ASIEP did it most clearly. If you need to rule out ID, these two are your best bet.

Pilowsky et al. (1998) later showed CARS agrees with the newer ADI-R 85% of the time. That backs up the 1986 finding—CARS keeps looking solid.

Sappok et al. (2013) tested adults with ID and found ADOS over-catches autism while ADI-R is stricter. Their message: pick the tool that fits the client’s age and language level, just like B et al. did.

Sasson et al. (2022) pushed validation further by testing deaf adults with ID. They proved you can still screen accurately if you tweak the items—echoing the 1986 call to choose tools with the sharpest cut-off.

When you sit down with a child who may have both autism and severe delays, start with CARS or ASIEP. They have the longest track record for separating the two. Keep ADI-R or ADOS in your pocket for extra detail, but let these old workhorses do the first pass.