How Ethnicity Is Calculated
Debbie explains why we can get very different estimates from different companies
The companies estimate your ‘ethnicity’, or more properly your biogeographical ancestry, by comparing your DNA with reference populations comprising people with known ancestry from specific countries or regions. The populations are collected from publicly available datasets and from the companies’ own customer databases.
You are given percentages indicating how much of your DNA you share with your closest reference populations. If you have ancestry from a particular population that is not included in the dataset then you will be matched with the next closest population.
The results will generally conform with your family history at the continental level, but will be less reliable at the country or regional level. Endogamous populations – those where people have been marrying within their own community for hundreds of years – tend to stand out as distinct genetic clusters. For this reason Jewish ancestry, and sometimes Finnish ancestry, can be detected with reasonable confidence. If results indicate that you are 50 per cent Jewish then you are likely to have a Jewish parent. Each company uses different reference populations and different algorithms, so results can vary considerably. You might get 10 per cent Italian or Norway at one company that doesn’t show up anywhere else.
Expect to see results updated from time to time as companies add reference populations and improve their methodology. In September 2018 an AncestryDNA update resulted in dramatic changes for many users.