The Harris-Todaro model was created to explain how internal migration occurs from rural to urban sectors through the difference in the expected wage. Pritchett points out that migration can benefit developing countries and their population much more significantly than any aid attempts. Industrial world transfer are around $70bn a year in aid, but by simply allowing a 3% rise in their labour force (taken up by migrants), the gains would be $300 billion: 4.5x greater. Fundamentally it was used to explain migration within an economy, but we attempt to expand the model to an international level. The model begins by accepting that the assumption of (near) full employment in urban labour markets isn’t particularly appropriate for developing countries which are beset by a chronic (under/)unemployment problem whereby many uneducated and unskilled rural migrants cannot find a job in the formal sector so become unemployed or join the informal sector. Thus in deciding whether to move to the city or stay at home on the farm, an individual has to weigh up the probability and risks of being unemployed for a considerable period of time against the positive urban-rural real income differential.