STEM majors are less liberal. Non-STEM majors are both more liberal and subjectively graded. We are also talking about undergrad vs grad-students. Lots of factors not considered as far as I saw at a scan.
In some defense of my discipline and others, students aren't "subjectively graded." I know what you're trying to say, which is that humanities classes typically don't administer multiple choice exams with correct and incorrect answers.
First, grading essays isn't subjective. There are identifiable rhetorical/stylistic qualities that make an essay good or bad. There are also identifiable conceptual qualities that make an essay good or bad.
I understand that grading is the most tangible way to measure discrimination, I also think it's a tad limited in scope. This definition of discrimination would probably be laughed out of any serious discussion about discrimination. It implies that it doesn't matter how you get from point A to point B, so long as you eventually get to point B, but I would argue that discrimination is just as much about what occurs between the two points.
This is a fair point; there's no way the data can account for strategies taken along the way, whether they be something unfair that occurs between teacher and student, or something unfair on the student's part (e.g. cheating).
I do think it's suggestive, to say the least, that students who identify as conservative and whose work exhibited perspectives we would likely classify as conservative (which, it seems to me, is what the study looked for) didn't suffer overwhelmingly from worse grades than did their liberal/progressive classmates.
The article also pointed out that there are some likely reasons for occasional differences in grading between liberal and conservative students, namely the kinds of thinking they bring to the table. Taking my field as an example: it's true that liberal-minded students tend to be good at finding contradictions and conflicting perspectives in texts, and discussing those perspectives in an analytical way. Less liberal-minded student tend to look for "messages" in texts, or "arguments"; in fact, this is most freshman undergrads. I can't count the number of times I've had to remind students that works of literature don't contain arguments. Or rather, they don't contain/promote just one argument. It's a matter of education and maturity to be able to sift through confusion and contradiction and articulate a focused point that isn't a proclamation about a text's "message."
It's just a ridiculous attempt to prove anything. How does one assert themselves as a MAGA fan while writing basic lit and history papers?
For what it's worth, "MAGA" doesn't necessarily equal "conservative."
And students love to express their political beliefs in undergraduate writing. They find ways.