hypothesis of the coefficients _0,_1,_2 being zero, but we fail to reject the null hypothesis of _3 (the coefficient on ERSP) being zero. The positive sign for SCL makes sense as it implies that educated people have more earning power. Income substitution argument implies that both NEIN and ERSP should have negative coefficients. However, this is not the case for NEIN. One possible reason is endogeneity: both WPH and NEIN may be driven by some common exogenous factors such as available opportunities and ability levels