In 1983, Lee sparked the 'Great Marriage Debate' when he encouraged Singapore men to choose highly-educated women as wives. He was concerned that a large number of graduate women were unmarried. Some sections of the population, including graduate women, were upset by his views. Nevertheless, a match-making agency Social Development Unit (SDU) was set up to promote socialising among men and women graduates. Lee also introduced incentives such as tax rebates, schooling, and housing priorities for graduate mothers who had three or four children, in a reversal of the over-successful 'Stop-at-Two' family planning campaign in the 1960s and 1970s. By the late 1990s, the birth rate had fallen so low that Lee's successor Goh Chok Tong extended these incentives to all married women, and gave even more incentives, such as the 'baby bonus' scheme.