Developed ability is the ability of children to learn. It is something that they have developed over their lifetime and that they will continue to develop. We measure it using a combination of their language acquisition (picture vocabulary) and a non-verbal test.
InCAS composite measures are a kind of average of the subtest scores that make up the whole assessment. The specific relationship between the subtest scores and the overall score is determined using regression analysis. Sometimes when the subtest scores are very similar the overall score is more extreme. This may seem counterintuitive, but a way to think about it is like this. Suppose one child was very good at Picture Vocabulary such that they were in the top 5%, and similarly a second child was found to be in the top 5% for Non-verbal Ability. Both children would be regarded as able in those particular areas. Now consider a third child with a Picture Vocabulary Score that was the same as that of the first child, and a Non-verbal Ability score that was the same as the second. Such a child is more able than either of the other two and will in consequence receive a higher overall Developed Ability score.