Education returns of wage earners and self-employed workers: Comment

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.