A 9-year-old child with an IQ of 130 has about the same intellectual ability as a 100-IQ adult. That is, they answer questions of the same difficulty with the same probability of success.
IQ scores are relative and usually age-normed. But because Rasch scores put a person's ability and an item's difficulty on the same absolute scale, you can compare a child and an adult by the same underlying level of performance rather than just their age-normed IQ.
This shows many interesting facts. For instance:
- A 10-year-old at 145 IQ and a 13-year-old at 130 IQ are at the same level of intellectual ability.
- The difference between the smartest and least intelligent adults in a representative group of 40 people is roughly as large as the difference between an average adult and an 8-year-old child.
The graph was made using data from the Woodcock-Johnson IV Technical Manual, by Enon Harris.
You can check out his page here: https://mindsbasis.blogspot.com