Reason Foundation

In 1960, there were 1.55 males for every female undergrad, but by 2003 there were 1.3 females for every male undergrad. What happened?

In The Homecoming of American College Women: The Reversal of the College Gender Gap (NBER Working Paper No. 12139), authors Claudia Goldin, Lawrence Katz, and Ilyana Kuziemko offer some explanations for the change.

Summary here.