Income is a poor measure of college education. The problem is that the valuable benefits of college are difficult to quantify; income has importance and is quantifiable, so I understand the temptation to use it as a metric, but it doesn't represent of the values of a college. It's like using the number of lines of code as a metric to represent the value of a piece of code - it's quantifiable, significant in some ways, but not representative of the code's value.
I much prefer the Times Higher Education model, especially their reputation survey. They survey 10,000 tenured and published academics worldwide, using what looks like well-designed methodology [1]. These are people in a position to have expert knowledge about the qualities of various universities. Yes it's imperfect and those people have bias too, but I can't think of a better model:
https://www.timeshighereducation.com/world-university-rankin...
One excellent alternative is Washington Monthly's rankings. Their approach:
We rate schools based on their contribution to the public good in three broad categories: Social Mobility (recruiting and graduating low-income students), Research (producing cutting-edge scholarship and PhDs), and Service (encouraging students to give something back to their country). More here:
http://www.washingtonmonthly.com/college_guide/rankings-2015...
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[1] https://www.timeshighereducation.com/world-reputation-rankin...