The College Scorecard Documentation Report repeatedly mentions that some data only represents undergraduates that are recipients of Title IV federal aid:
Most of the metrics of institutional performance described in this appendix—those based on data in the NSLDS, or matched earnings data for students appearing therein—are based on undergraduate students receiving federal aid. Moreover, institution-specific measures of debt, default, and repayment are based on the subset of students with federal loans.
What is the best way to determine the concrete subset percentage used for a given measure? Is it a "cohort" column, like
Number of students in the family income cohort?
If so, why do the cohort sizes vary so drastically? The family income cohort size is usually about 10-20%, while others are much higher.
Finally, why is the earnings cohort size (
COUNT_ED) always NULL?
A Broader Problem
I'm investigating this question because I want to determine how representative some data fields are of the entire undergraduate body. For example, the data shows that Harvard is incredibly economically diverse: its median family income is $33.07K! This is very hard to believe, and I'm trying to explain this phenomenon. Is there a better way to do this?