In a recent paper, García-Mainar and Montuenga-Gómez [García-Mainar, I. & Montuenga-Gómez, V. M. (2005). Education returns of wage earners and self-employed workers: Portugal vs. Spain. Economics of Education Review, 24(2), 161–170] apply the generalized IV model of Hausman and Taylor to estimate education returns of wage earners and the self-employed in Portugal and in Spain. Our examination reveals several problems which relate to the validity and documentation of the instrumental variables, as well as the robustness of the results.
In their reply to our comment, García-Mainar and Montuenga-Gómez [García-Mainar, I., & Montuenga-Gómez, V. M. (2009). A response to the comment on education returns of wage earners and self-employed workers. Economics of Education Review] did not address our fundamental criticism that they have not provided the information necessary to replicate their study.
