In July 2013, there were 41,000 non-Germans by citizenship living in Thuringia (1.9% of the population − among the smallest proportions of any state in Germany). Nevertheless, the number rose from 33,000 in July 2011, an increase of 24% in only two years. About 4% of the population are migrants (including persons that already received the German citizenship). The biggest groups of foreigners by citizenship are (as of 2012): Russians (3,100), Poles (3,000), Vietnamese (2,800), Turks (2,100) and Ukrainians (2,000). The amount of foreigners varies between regions: the college towns Erfurt, Jena, Weimar and Ilmenau have the highest rates, whereas there are almost no migrants living in the most rural smaller municipalities.
What was the decrease in non-German population between 2011 and 2013?