Immigration to the DRC has decreased steadily over the past two decades, most likely as a result of the armed violence that the country has experienced. According to the International Organization for Migration, the number of immigrants in the DRC has fallen from just over one million in 1960, to 754,000 in 1990, to 480,000 in 2005, to an estimated 445,000 in 2010. Official figures are unavailable, partly due to the predominance of the informal economy in the DRC. Data are also lacking on irregular immigrants, however given neighbouring countries' ethnic links to DRC nationals, irregular migration is assumed to be a significant phenomenon.