V. Joseph Hotz (Duke University, Department of Economics), Peter Arcidiacono (Duke University, Department of Economics) & Songman Kang (Ph.D. Student, Duke University, Department of Economics) have posted Modeling College Major Choices Using Elicited Measures of Expectations and Counterfactuals on SSRN. Here is the description of the paper from the May 2010 NBER Digest:

Although various studies have documented differences in earnings across college majors, comparatively little is known about how students choose their major. [This paper finds] that both expected future earnings and students’ assessments of their own abilities affect their choice of a college major. However, students’ forecasts of expected earnings in different majors are often incorrect. This study estimates that 7.5% of students would switch majors if they made no such forecast errors.

The data for the study come from a 2009 survey of 173 Duke University male undergraduates. The survey asked students to estimate earnings ten years after graduation in a variety of professions, or for students majoring in particular fields, as well as what the respondent expected to earn in his major and how much his earnings would have to change in order to entice him to switch majors. The students who completed the paid survey were more likely to receive financial aid, major in science, and be of Asian ethnicity than the rest of the Duke male student body.

In modeling students' choices, the authors find that if abilities were assumed to be equal, students would move from the Humanities and the Social Sciences (other than Economics) into Engineering because of the higher expected earnings from an Engineering major. In fact, the share of individuals choosing Natural Science or Engineering Majors increases by 5.5% and 10% respectively when expected earnings increase by one standard deviation. If expected earnings were equal across all majors, then the students choosing Humanities and Social Science majors would increase by 17%  and 10% respectively, while those choosing Economics majors would fall by 16%.