Makes a lot of sense except they need a section for different incomes in there.
Agreed, but income is harder to get good accuracy.
For instance, people who go to church every week are proud of it.
People who go to school are proud of it (and it can be checked rather easily).
People who vote for someone are proud of it.
Income however is a more sensitive question and more prone to lying/exaggeration or any form of deceit.
I am rather confident that it was not conducted because it would be an intrusion on privacy to conduct a background examination or that the statistics were too prone to participant bias to accept the results.