This figure shows that right below the test-score cutoff, 20 percent of students went to college. Right above, it’s 40 percent. The difference — 20 percentage points — is the estimated causal effect of loan availability on college attendance.

The South African study reaches a similar conclusion. Right below the credit-score cutoff, 50 percent of students went to college, compared with 70 percent right above. Again, the estimated effect is a 20-percentage-point increase in college attendance.

These are enormous effects. The papers show that student loans make college possible for many students, at least in these two countries. The effect may be smaller in the United States, or it might be larger. I’d wager that student loans open the doors of college for millions of American students who could not otherwise attend.

If we want to know the benefits of offering loans (versus not offering them), we need to take this enrollment effect into account. The relevant question to ask is not: Would you be better off with another $50,000 in your bank account? Rather it’s: Would you be better off with no debt and no degree?

My guess: “No.” The payoff to college is enormous, and much larger than the typical student debt.

There are some students who would have gone to college even without a loan. They took one anyway so they could attend a more expensive college (or to work less). Are they worse off with loans than without? For these students the relevant question is: Would you be better off with no debt, having gone to a cheaper college?

Here, the answer is less clear. If the pricier college is much better at teaching and getting students to graduation, the debt could be worth it. If the pricier college is no better (or even worse), then the debt is not worth it. In the latter case, I have in mind students choosing between community colleges and for-profit colleges, which offer similar types of courses but differ vastly in price. The jury is still out on whether for-profit colleges are much worse than community colleges, but the evidence we have so far definitely doesn’t suggest that they are much better.

I will end with another uncontroversial proposition: Students would be happier, all things equal, if college were free. In the not-so-distant past, prices at public colleges, particularly at community colleges, were close to zero. Taxpayers made those low prices possible, with states using that tax revenue to keep prices low at their public colleges. Taxpayers and states have cut back on their support for public colleges, and students now pay a higher share of their college costs than they once did. They’re not happy about it.