Complex sentence: Since 1974, there has been a huge "white flight" out of the suburb as more immigrats were assigned there, by 2012, the figure for those of "immigrant background" was given as 86%.
Split into simpler sentences: Since 1974, there has been a "white flight" out of the suburb as more immigrants were assigned there. By 2012, the figure for those of "immigrant background" was given as 86%.