I meant to add that the Bowen & Bok book is chock full of data supporting their critique of early admissions. At this point, since the book is more than 10 years old, it’s old data, but there it is.
SES data for a particular college is very hard to come by. Colleges don’t like to publicize that. People use proxies like percentage of students receiving financial aid (but schools differ significantly in the income/asset levels at which they phase out financial aid, so it’s not always apples to apples) and percentage of students receiving Pell grants (reflecting ultra-low-income students, but not the vast majority of working- or middle-class Americans). ProPublica has a nice website where it’s possible to compare individual colleges on that basis, but the data is 5 years old, so it may be a while before one can assess the impact of ED on Chicago.
And, in any event, I’m not certain what colleges you are going to want to compare to Chicago. MIT is the only peer with no ED or SCEA, and a very limited EA program. (MIT has never handed out anywhere near half of its acceptances in the EA round.)