I was told by a few ancestry.com reps that they tested people that they "verified" were of a certain ethnicity, and set their DNA as the standard. Then they compared other participants' test results to the standard.
Many other companies gather DNA from groups around the world and test it over and over to make sure that they have a clear baseline. I don't think ancestry.com did this.
I think Scandinavian is a term they are using to encompass a lot of other countries that they haven't yet determined. I took a DNA test previously and I have very, very little Scandinavian DNA (like 2%), yet ancestry DNA says I have around 15%.
They also group all African Americans as as "West African." I took a DNA test a while ago and learned that a lot of my ancestry came from Morocco, yet I don't see anyone else with results like that. Also, I know my Haplogroup and Blood type, and while I am African American, my info reflects more Iberian/N. African DNA than it reflects Western African DNA. All parts of the continent are equally beautiful, but I took the test to connect with other members who reflect similar DNA; not be lumped together with every person of Color. I've been told that a few people have results from other parts of Africa, but they mainly just group everyone all together based on their previously set "standard."
It makes me wonder if they truly look at members' DNA matches and establish connections, or if these connections are based on last names and matching regions. The whole thing is rather strange. Still, I've established connections with other members with whom I share a great grandparent....so maybe the test really is onto something.