The value difference between Karson's worsened behavior at the end of the 12 weeks versus the promise to cure Karson of ADHD can be described as a measure, in part, of

Expectation interest.

Explanation:

As it is seen that this is directly a human disorder that denies Karson of a lot of social balances which ranges from paying attention, loosing social balances etc. The value difference can be tagged an expectation interest from the affected person. And it is seen to always aid in thinking, sizing up, and also make sense of individuals, groups of people, and the relationships among people.Sometimes when we have knowledge that someone is friendly and interested in us, we are likely to approach them; if we have learned that they are threatening or unlikable, we will be more likely to withdraw. And when he has done wrong, we may process new information in a manner that helps convince us that our judgment was correct.

fertile good for trade etc