Jansen and Piermartini (2005) show that the temporary movement of persons, by reducing transaction costs for merchandise trade between home and the host country, causes bilateral trade to expand in a statistically significant way. Walmsley and Winters (2005) have focused on the direct welfare effects of liberalising trade in mode 4 in a general equilibrium framework. They show that if OECD countries allowed temporary migration of workers to increase by the equivalent of 3 per cent of their labour force, the resulting global gains would be greater than those under full liberalisation of merchandise trade. Moreover, both developed and developing countries would share in the gains, which would be largest if migration of both professionals and unskilled workers were permitted.