There is no official figure for the number of immigrants living and working here in the last 15 years of what has been for Greece an unprecedented phenomenon of immigration. This applies to both illegal and legal immigrants. Yet data from initial studies carried out for the Immigration Policy Institute (IMEPO) indicate a total figure of about 900,000, although other surveys see this figure rising to about 1.2 million. The same surveys show that for every legal immigrant, there is also an illegal one – a one-to-one ratio. Most of these immigrants have been in Greece for over five years. They come from 27 different countries, although 55.6 percent are Albanian and another 17 percent are from other eastern European countries. In the last 15 years, the immigrant population has quintupled; just over the past five years, the number of children of immigrants attending Greek schools has tripled to 150,000. According to IMEPO, one in 10 high school pupils in Attica is the child of an immigrant and the ratio is rising. Although the general high school population for 2004-2005 in Attica dropped by 8.9 percent over the previous year, the foreign pupil population rose by 20.8 percent. Most are concentrated in the municipality of Athens, where they comprise about 18 percent of pupils, compared to just 6.5 percent in schools in the northern suburbs. Around 80 percent of the foreign pupils are from Albania, followed at some distance by Russia with 2.8 percent.