Why that college-major salary study doesn't tell all

Time magazine tells humanities supporters not to be too pessimistic about the Georgetown study of highest-earning majors:

Before switching majors or pushing your child into petroleum engineering (the highest-earning major, with a median salary of $120K), however, make note of one flaw in the Georgetown study. The median salaries in the report do not factor in graduate degrees in any way. Those who received something beyond a bachelor’s degree are not represented—English majors who went on to be lawyers, for instance, or Sociology majors who later earned MBAs. For that matter, it’d seem like most full-time school teachers—the vast majority of who wind up with advanced degrees—are not included either.

The study notes that about 40% of Liberal Arts and Humanities majors obtain graduate degrees, and with them a bump up in salary, so maybe all of the engineers aren’t out-earning the English majors by quite as much as the report indicates.