Following up on a suggestion by Fabio Rojas, I went to this page and selected the study that looked at college graduates from 1999-2000 and interviewed them in 2001. I just did a simple table of annual job income by college major.

Major average income 25th percentile not in grad school
25th percentile
Humanities 23791 11900 15600
Social Science 23361 9840 18000
Life Science 20120 0 17500
Physical Science 25003 15000 22000
Math 31063 20000 23000
Computer Science 43028 29800 30000
Engineering 40683 31000 35000
Education 25184 20000 21000
Business 35346 25000 27000
Health 31331 18000 25000
Voc-tech 30682 23000 23700
other tech-prof 27008 15600 20000
overall 28478 15840 21000

Pulling up the average are computer science, engineering, business, health, math, and vocational-technical. Pulling down the average are life sciences (why is this so low?), social sciences, humanities, physical sciences (again, why so low?), education, and “other technical/professional.”

If the ultimate question is whether more students should attend and graduate from college, then perhaps what should interest me is something like the income of the lowest 25th percentile within each major. That might give a better idea of what we might expect to see at the margin if more students graduated college in the various majors.

At the 25th percentile, the really bad majors are life sciences (again, what are these, and why do they do so poorly?), humanities, and social sciences. Perhaps the 25th percentile of these three groups is what defines the unskilled college graduate. Note how much better vocational-technical looks at the 25th percentile.

[UPDATE: I re-ran the numbers, taking out of the sample anyone who was enrolled either part-time or full-time in a post-graduate program. See the far right-hand column of the table. The unskilled grads are not such extreme outliers if you do this, but they still are not doing very well.]