Genetics
In 2011, a detailed genetic study was made in order to, among other reasons, see how similar the Sweden Finns were to the native Swedes. Each samples in the study were looked at individually, to make sure that the Swedes had full grandparental ancestry from their represented Swedish regions respectively, and the Sweden-born Finns having all of their ancestry from Finland. The Swedes who showed the closest FST distance (meaning greatest genetic similarity) to the Sweden Finns were those from East Middle Sweden and North Middle Sweden, having distances of 4.66 and 4.67. The most similar Swedes after those were the ones from Stockholm (4.81). Upper Norrland was the second most distanced (and thus one of the most dissimilar), at 5.61, which was quite surprising due to the fact that this region likely is where Swedes and Finns have been in greatest contact with each other.
The greatest FST distance between the Swedes and the Sweden Finns was 5.63, and that accounted for the Swedes who came from the southernmost regions. The greatest FST distance within the Swedish group as a whole, for comparison, was between Southern Sweden and Upper Norrland (3.19), despite Upper Norrland being one of the most distanced Swedish groups from the Sweden Finns as well.
Read more about this topic: Sweden Finns