That’s a fair point.
What data we do have, though imperfect, seems to back this trend up. The Maroon’s Class of 2020 survey has data on family income (the class of 2021 article doesn’t include a detailed breakdown, so I’m using the 2020 figures). The survey had a response rate of about 1 in 3 students - pretty good as such things go. Political pollsters, by way of comparison, are overjoyed if they get a response rate of 5%. This allows some comparison with tax data for the class of 2013.
Link: https://www.chicagomaroon.com/article/2016/9/14/class-2020-survey/
Per the NY Times interactive, about 58% of the Class of 2013 had parents in the top 20%.
61.78% of respondents in the Class of 2020 survey reported household incomes over $150,000. Another 14.83% reported incomes between $100,000 and $150,000. The 80th percentile for household income in the U.S. was about $117,000 in 2015, so it’s not outlandish to say half of the 100-to-150K group - a tad over 7% - had household incomes above the 80th percentile. That would put the share of households in the top 20% at approximately 69% for the class of 2020. With less conservative assumptions about the distribution within the 100-to-150K bucket, that might be 70% or 71%. The error bars around this estimate are pretty wide - but it’s evidence, however tentative, for a wealthier class of 2020 compared to the class of 2013.
This table from the Washington Post, based on data reported to U.S. News and World Report, compares the share of students eligible for Pell Grants in the class of 2014 and the class of 2019: http://apps.washingtonpost.com/g/page/local/pell-eligible-share-of-freshmen-at-top-colleges/2245/
Chicago’s class of 2019 had a Pell-eligible population of 12% of the student body - a 3% drop over five years. That was lower than Harvard (16%), Princeton (17%), Yale (17%), Stanford (13%), MIT (15%), Columbia (17%), Cornell (15%), UPenn (14%), and Brown (13%). Even Northwestern (15%) had a higher share of Pell Grant recipients. Our 12% was tied with Duke (also 12%) and higher than Notre Dame (10%) or Cal Tech (11%).
US News & World Report data for the Class of 2020, a year later, shows another drop in the Pell-eligible population - to 11%: https://www.usnews.com/best-colleges/rankings/national-universities/economic-diversity-among-top-ranked-schools. That put us below Duke (13%) and Cal Tech (12%), in addition to every school I mentioned above except Notre Dame (still 10%). UChicago had the third-lowest share of Pell Grant recipients among top-25 schools - just ahead of Notre Dame and Washington University in St. Louis (also 10%).
None of these data are definitive, but every individual piece of information points in the same direction, and what longitudinal comparisons we have (courtesy of the US News numbers and the Post’s ranked table) suggest socioeconomic diversity at UChicago has dropped and now lags most of our peers.
I have my thoughts on this, but that’s a topic for another day.