“…affect the worker's earnings positively (Goldsmith, Veum, & Darity, 1997;Groves, 2005;Heckman, Stixrud, & Urzua, 2006;Mohanty, 2009;Mueller & Plug, 2006;Nollen & Gaertner, 1991;Nyhus & Pons, 2005;Salgado, 1997;Waddell, 2006). Interestingly, these psychological variables in most studies not only assume statistically significant positive coefficients, but also have predictive powers higher than those of the standard human capital variables (Goldsmith et al, 1997;Mohanty, 2009;Nyhus & Pons, 2005), indicating the importance of these variables in the estimation of wage equations.…”