PROFESSORS at Harvard University used to be vicious examiners. In 1950, according to one source, its average grade was a C-plus. Today things are different. The median* grade is A-minus: the most commonly awarded grade is an A. Yale's may be little better: from 1963 to 2008 the average grade increased by 37%. (We can't verify any of these stats, and comparing over time is fraught with difficulty; but you get the idea).

Grade inflation gets some cogent defences. It may reflect harder-working students. But it irritates many—particularly those who don't benefit from it. There is even a website that allows Princetonians, who are marked notoriously harshly, to compare themselves to cosseted Crimsons. The nerdiest Harvard students have their own complaints: when lots of students are squashed together at the top, they say, separating out the top scholars is trickier.

Some colleges have pursued anti-inflation policies of which Paul Volcker would be proud. In 2004 administrators at Wellesley College, a prestigious, women’s-only university, mandated that in introductory and intermediate courses (with at least ten students) the average grade could not exceed a B-plus, equal to a grade-point average of 3.33. Three economists look at the impact.

Only courses in high-grading departments in the humanities and social sciences needed to change grading practices: science subjects were unaffected by the policy. That gave the economists a good “control", allowing for a meaningful analysis of the policy.

What happened? Previously generous departments became more tightfisted. Students were 14% points less likely to get an A in the treated departments (though they were no more likely to get a C-minus or below). Lots more Bs were given.

The graph below gives a flavour of the results (the green lines show when the policy was introduced then implemented; the dashed red line shows the 3.33 target).