Estimating causal effect for educated people on wages I have a problem regarding causation and effect. I have a linear model 
$ wage=\beta_0+\beta_1educ+\beta_2female+\beta_3hourseworked+errorterm$
When I need to estimate the causal effect for educated people on wages, I have chosen a subpopulation educ==1 (educated people) and made a regression in stata.
The used commands are 
reg wages educ female hourseworked

From this regression I obtain 0 for the educated people, and it says that it is omitted. How can I find the causal effect of educated people on wages, when I have this problem? 

I have tried to remove the intercept, from which I get an estimate causal effect of education, but is it correct just to remove the intercept? 

Do I have to think about endogeneity - omitted variables - instruments?
Yes, you have to worry about the difference between correlation and causality. In these situations, it helps to try to force a case of ommited variable  bias.

In this case "talent" or "effort" is unobserved. Both this might make people more likely to pick up additional education, and also be more successful at their jobs.

Or family background: If your parents are high achievers, they might induce you to take more education, and they also are well-linked to ensure you get a well-paid job.