Contents
What is endogenous sample selection?
The basic example of Endogenous selection is that the selection of a sample is based on the value of a Variable which depends on other Variables of interest. Endogenous selection occurs if the selection of the sample depends on the values of occupational success.
Why is endogenous sample selection a problem?
Endogenous selection bias is a central problem for causal inference. Endogenous selection bias can result from direct conditioning on the outcome variable, a post-outcome variable, a post-treatment variable, and even a pre-treatment variable.
What is the difference between Endogeneity and selection bias?
In general, sample selection bias refers to problems where the dependent variable is observed only for a restricted, nonrandom sample. Endogeneity refers to the fact that an independent variable included in the model is potentially a choice variable, correlated with unobservables relegated to the error term.
What is self selection in research?
A sample is self-selected when the inclusion or exclusion of sampling units is determined by whether the units themselves agree or decline to participate in the sample, either explicitly or implicitly.
Which is the second stage of Heckman selection?
Equation (2) is basically the First Stage and Equation (1) the Second Stage of the IV estimation suggested above. However, the problem is: Whether Y1 and Y2 are observed, does also depend on many of the same regressors Xb, Xc, Z2, which I think would call for a Heckman selection model.
Is the selection problem caused by Y or X1?
X1 may be reversely caused by Y. On its own, I would solve this problem by instrumenting X1 with instrument Z1, which is exogenous to Y: Whether Y is observed, may also depend on X1, i.e. I have a possible selection problem.
Why is it important to control for sample selection?
Since X2 is observed only for individuals who are working, I think it is important to control for sample selection, because the decision to work is not random and hence individuals who are working may be systematically different from individuals who are not working.