"Average Oath Income"
("Average Estate Income" for the new system...)
Nice hint dropping you did there....
I wonder if the median income wouldn't be better? After all, if the problem is income inequality, the average won't tell you anything; the non-Lord average gives you a very specific information that may not paint the whole picture. In many realms, city estates could skew the average up, but could be reserved to a closed elite.
Would it be thinkable to code the Gini coefficient of a realm?
