Flagstaff, AZ – A new report shows that Arizona's population of illegal immigrants has fallen by 1/3 over the past two years. The report was compiled by the Center for Immigration Studies. It says undocumented immigrants are leaving Arizona and returning to their home countries because of the state's poor economy and tougher enforcement of immigration laws. In 2007, researchers say the number of undocumented immigrants in Arizona was about 530,000, but, since then, that number has dropped to about 350,000. Some researchers outside the study are disputing the findings. A report issued last week by the Pew Hispanic Center found that immigrants, both legal and illegal, are not leaving the country. The report used analysis from government population surveys from the U.S. and Mexico and Border Patrol Apprehensions Records.