References
- Bagnoli , M. and Bergstrom , T. C. 1993 . Courtship as a waiting game . Journal of Political Economy , 101 : 185 – 202 .
- Heckman , J. J. 1997 . Instrumental variables: a study of implicit behavioral assumptions in one widely used estimator . Journal of Human Resources , 32 : 441 – 62 .