http://www.legalgenealogist.com/blog/2013/10/27/those-pesky-...This is a good blog post on how to not get too hung up on the ethnicity percentages.
(I was a poster child of WTF in the original version before they revamped the percentages. 90% Scandinavian for me while my mother had only 10%. The revamped percentages are better but still screwy.)
Elizabeth