I was really taken back by the fact staggering 64% Great Britain number. After reviewing some information, I learn how this information is calculated at Ancestry.com and how this compares to other people.
The DNA markers for each region are compared to 40 different samples of your DNA (40 random segments of your DNA are sampled and compared). This sampling is done on each of the 26 global regions. The results for each region are essentially weighted to determine the total percentage.
The 3,000 DNA reference markers are taken from people living in that region where many generations of grandparents are all from that county/region.
So I viewed the actual percentages and found my ranges as such:
Great Britain: 64%, Range: 45%-84%
Europe East: 17%, Range 8%-26%
Scandinavia: 8%, Range 0%-20%
Europe West: 4%, Range 0%-17%
Ireland: 4%, Range 0%-12%
Asia South: <1%, Range 0%-2%
Finland/NW Russia: <1%, Range 0%-4%
European Jewish: <1%, Range 0%-2%
Additional notes of interest are that a typical native of Great Britain has a 60% DNA match for that region, but I matched at 64%.
In an ideal world where every person gets half of their DNA from each parent where that DNA is exactly made up of 50% of each parent’s DNA and their parents are exactly 50% of each of their parents and so on. In the real world, the 50% from your father may be an uneven split of the DNA they received from his parents. The variations in the percentage for Scandinavia can easily be explained by DNA passdown model I just explained, but that model also means there probably is more Great Britain ancestors hidden in other areas of my family tree.
While researching and trying to understand the results, I found a tool at GEDMatch.com to explain the admixture (ethnicity estimate) in better terms (sort of).
GEDMatch allows you to compare your mixture with a European-centric DNA comparison group. The difference between this DNA comparison and the Ancestry.com version is that the GEDMatch uses real world samples of typical popuations with an array of past ancestry and they validate the results against actual family trees.
The result statistically match your results with populations of the countries studied to see what countries closely match your DNA. The first picture shows the admixture percentages that don’t make any sense to a layman followed by the closest heritage matches based on that admixture result. The second pictures shows the same information, but only when the test group are of 2 different populations.
Essentially, the results show the my closest match (Distance) for a single ancestry is Norwegian. For a mixed ancestry, I really match close to Norwegian (and West Norwegian [Fjords area]) and East German. Now these results make much more sense. Based on my quit search, I found that the West Norwegian area had the highest immigration to the plains states of the USA.