In relation to internal migration, according to the 1910 census, 300,000 or almost 10% of the ethnic Bulgarians were born in another Bulgarian municipality than the one they were enumerated in. The same data shows that the foreign-born ethnic Bulgarians numbered 78,000, or 2% of them, most numerous of whom were the 61,000 Ottoman Empire-born, 9,000 Romanian-born and by less than 2,000 Austro-Hungarian Empire, Serbian and Russian-born. By the 1926 census, there had been 253,000 refugees with granted households and land or citizenship but with many more in towns of uncertain number. 35% came from Eastern Thrace, 30% came from Aegean Macedonia, another 18% from Western Thrace, 8% from Dobruja, 4% from the Western Outlands, 3% from Asia Minor, and 2% from Vardar Macedonia. They constituted 6% of the countrys population. In 1940, 70,000 Bulgarians were exchanged from Northern Dobruja. The total number of refugees in 1878-1940 is estimated at between 700,000 and 1,200,000.. How many years was the time span where it is estimated that the total number of refugees is estimated between 700,000 and 1,200,000?