The wage that a worker receives is observed only when he/she is employed. The employment of the worker, however, depends on two sequential decisions: the worker's decision to work and the employer's decision to hire. The wage sample, thus, is obtained through a double selection process....

Following the technique of bivariate probit with partial observability, I find the evidence that one reason US workers queue for local government jobs is to obtain union status. The average desire probability for local government union jobs is found to be twice as large as the desire probability...