In response to the questions about how they got your family income - If you look at the data notes in the papers, they start with the Social Security “Death Master file” to find everyone by their birth year. Colleges are required to report to the IRS on Form 1098-T about every student who does not have tuition waived so that taxable scholarships can get taxed. After the researchers matched the SSA death file and the 1098-Ts, the researchers looked up dependents claimed on tax returns in the IRS Databank to get at parental household income. Only US taxpayers are included, so well-heeled internationals students are not counted in these analyses. They are also prohibited from reporting actual data from fewer than 10 tax units. So they cannot report the exact number of students at a particular income level at an individual college (though they have the data). Instead they created a regression model based on the overall data and then applied that model to the characteristics of individual colleges. That’s why they are careful to say their individual school income breakdowns are estimates.
On why it matters that so many students come from the top 1% versus the bottom 60% - We think of college as a driver of economic mobility. Elite schools claim to educate the future elite. They don’t claim to be only for those that were born to elite parents. But, all these colleges get an enormous amounts of public money in the form of financial aid and research funds and tax exemptions on their endowments (biggest public subsidy for the Ivies) and most are exempt from local property taxes too. What responsibility do elite colleges have to provide opportunities for the large majority of Americans versus the 1%?