 Finally, in a popular article addressing questions around brain drain, McKenzie and Gibson highlight that brain drain has remained relatively stable over time, that skilled and unskilled migration are strongly correlated, that the likelihood of brain drain increases the lower domestic standards of living, security, political stability and opportunities for rewarding careers, and that examples of brain gain exist, among else.Another key area of McKenzie's research are (micro-)enterprises in developing countries and constraints to their growth.For instance, McKenzie and Christopher Woodruff find that start-up costs of Mexican microenterprises tend to be very low and returns to capital high, suggesting that entry costs are unlikely to provide an empirical basis for poverty traps.