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Should you borrow to go to college? It's just one of countless decisions you'll make about your education, and one of the most confusing. Borrowing could potentially open doors, but it might also backfire later. So what should you do? 

A long-term investigation into the salaries of science and engineering graduates provides some major food for thought. In short, student loan borrowers earn less money than non-borrowers -- but not for the reasons you might expect. 

It's all about grades
The researchers found that the single biggest factor that affects salaries is differences in grade point average. Borrowers have worse grades than non-borrowers, and it's the most significant reason they earn less after graduation.

In other words, lower earnings for borrowers don't come from things like demographics or financial constraints that force borrowers to go to worse schools. Though program quality matters a little bit, in the end it's mostly about grades.

This is most powerfully illustrated by looking only at disadvantaged students, who all face similar financial pressures, and comparing borrowers to non-borrowers. Borrowers are 50% more likely to attend a higher-ranked program or private school, which means that they appear to place a larger bet on the benefits of those programs for their futures.

The results in a nutshell? Disadvantaged non-borrowers -- who attended worse schools, mind you -- leave college with salaries over 10% higher than borrowers.

Again, the majority of the reason came down to GPA. Borrowers had "drastically lower" grades than borrowers, which completely wiped out the potentially positive effects of going to a great school.

Why do borrowers have worse grades? 
The question of why borrowers perform worse is open to debate. Perhaps the financial stress of a debt burden means they need an extra job, or maybe, as I suggested, borrowers are overestimating the importance of school quality on their employment prospects. The researchers also suggest that student borrowers could be facing more pressure when they go to the job market, leading them to take a lower-paying or more secure job rather than holding out for something better.

Another possible explanation, which Malcolm Gladwell explained in depth in the book "David & Goliath: Underdogs, Misfits, and the Art of Battling Giants", is that going into a more competitive program isn't always in the student's best interest. 

Gladwell cites research that shows that more competitive science, technology, and math programs have a higher dropout rate than less competitive ones: A 10-point rise in the average SAT score of incoming freshman brings a 2% drop in retention. As Gladwell puts it, "The smarter your peers, the dumber you feel; the dumber you feel, the more likely you are to drop out of science."

Or, perhaps in this case, the more likely you are to do poorly -- and suffer the consequences. 

The lesson: Reconsider borrowing 
The bottom line: Your grades matter more for your future than where you go to school. 

For a variety of possible reasons, borrowing reduces grades. So if you really want to set yourself up for success in college, you might want to avoid the student loans and simply do the very best you can academically. 

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