Have you ever wondered why your grade point average is so high?   Is it because you close The Mudd every night? Your raw intelligence?  Your unusually good problem-solving skills?  Your avoidance of my classes?

Or maybe it’s because it’s 2010 and Lawrence is a private university.  It seems that the average college GPA has been going up at the rate of about 0.1 per year for the past 50 years, with private schools leading the charge.  Here’s Exhibit A:

That’s from the NYT‘s Economix column.  The green series is the GPA for private schools over time, which appears to have started at about 2.3 in 1930 and increased to right around 3.3 today.  That’s right, the average student at a private college has a 3.3. GPA.   The grey dots show the data points surrounding the series, so this is no selection bias problem.  In fact, the lowest average GPA in the sample (about 2.7) is higher than virtually every single recorded data point prior to 1950.

The big question, of course, is why?  The answer to that is probably not so simple.  We have seen one of the consequences, however — students really do work less these days.  Recent scholarship documents an inverse relationship between the expected average class grade and the amount that students work.  To wit: average study time would be about 50% lower in a class in which the average expected grade was an “A” than in the same course taught by the same instructor in which students expected a “C.” In other words, students are working less and getting higher grades.

One point of interest is that science classes have traditionally graded much more harshly than the humanities.

[S]cience departments today grade on average 0.4 points lower than humanities departments, and 0.2 points lower than social science departments. Such harsher grading for the sciences appears to have existed for at least 40 years, and perhaps much longer…  Relatively lower grades in the sciences discourage American students from studying such disciplines, the authors argue.

So does that account for the dearth of American-born scientists — the fear of getting a B?

How do you suppose a maximizing professor should think about these issues?  If I want to push my students, do I have to be a tough grader? Or do I just end up with fewer students grouching about how much work I give them?

Click on the “making the grade” tag for more on grade inflation.