The Feb 2020 Chetty study referenced in the original post emphasizes portion of students attending colleges, not portion accepted. Portion attending often has more to do with rate of applications for selected group than it does with acceptance rate for selected group.
The report mentions that Ivy Plus colleges had the following portion of students from different income quintiles at the time of the sample (1980-82 birth cohort).
Actual Income Distribution at Ivy+ Colleges
Highest Quintile Income – 68.4% of students
2nd Highest Qunitile – 13.4% of students
Middle Quintile Income – 8.7% of students
2nd Lowest Quintile – 5.7% of students
Lowest Quintile Income – 3.8% of students
More than 2/3 of students at Ivy+ colleges were from the top quintile of income, while only 3.8% were from the bottom quintile. This sounds bad. However, when they look at expected percentages based on SAT/ACT test scores, race, and state residence; then the distribution still remains skewed in favor of top quintile. Specific numbers are below.
Expected Income Distribution at Ivy+ Colleges Based on Test Scores +…
Highest Quintile Incomce – 57.8% of students
2nd Highest Qunitile – 18.5% of students
Middle Quintile Income – 12.1% of students
2nd Lowest Quintile – 7.3% of students
Lowest Quintile Income – 4.4% of students
If colleges gave a boost on SAT/ACT for lower/middle income students based on the lower expected SAT/ACT for lower/middle income students, then the percentages change to the following. This is the effect of a strong hook for being low income, and a significant hook for being middle income.
Expected Income Distribution at Ivy+ Colleges Based on Test Scores with Score Boost for Low/Middle Income Students
Highest Quintile Income – 34.3% of students
2nd Highest Qunitile – 21.2% of students
Middle Quintile Income – 17.2% of students
2nd Lowest Quintile – 15.5% of students
Lowest Quintile Income – 11.8% of students
I think the conclusion is highest quintile income students are more likely to apply to Ivy+ colleges, more likely to have qualifying SAT/ACT scores, and more likely to be accepted. This results in the top quintile income being dramatically overrepresented at Ivy+ colleges, as well as other highly selective colleges.
Lowest quintile income are the least likely to apply and by far the least likely to have qualifying SAT/ACT scores. The rare few who apply and have qualifying SAT/ACT scores may be slightly more likely to be admitted than middle income students with similar SAT/ACT scores. This is not inconsistent with other sources such as the Harvard internal report at http://samv91khoyt2i553a2t1s05i-wpengine.netdna-ssl.com/wp-content/uploads/2018/06/Doc-421-112-May-1-2013-Memorandum.pdf , which shows a significant admission boost for low income students (far less than boost for ALDC hooks). Specific numbers are below.
Harvard Admit Rate by Income
<$40k income: ~20% of applicants had 1500+ SAT scores. Expected 6% admit rate based on qualifications, actually had 11% admit rate
$40-80k income: ~25% of applicants had 1500+ SAT scores. Expected 8% admit rate based on qualifications, actually had 11% admit rate
$80-120k income: ~35% of applicants had 1500+ SAT scores. Expected 9% admit rate based on qualifications, actually had 9% admit rate