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 is the time span where the total number of refugees is estimated at between 700,000 and 1,200,000?