Why do I get different results from two DNA tests?

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07 May 2020
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Have you taken two DNA tests with separate companies and received different ethnicity results? Read on to find out why this would be.

Genealogy DNA expert Karen Evans helps Family Tree reader Lee Passmore with his test query.

I am writing as I have done two DNA tests, one with Ancestry last year and one with 23andme before Christmas. When I got my ethnicity results they were different to the Ancestry results. It says I am 99.7 percent European, and 0.1 percent Melanesian, which is from Papua New Guinea and the Solomon Islands, as well as 0.3 percent Egyptian and Arabia.

I would have expected some Middle East in me, but how Pacific Islander from the other side of the world, makes up just 0.1 percent of me is a mystery? Perhaps someone of Melanesian descent moved to Europe and married one of my distant ancestors, or I had an ancestor who was a sailor, travelling the world, stopping in New Guinea and marrying one of the natives?

By comparison, Ancestry said I was 100 percent European. Does this mean that 23andMe’s testing methods are more accurate than Ancestry’s?

Karen replies:

Lee’s question refers to ethnicity reports and their accuracy (or otherwise). Ethnicity is only as reliable as a company’s data. Ancestry and 23andMe explain that they estimate ethnicity by comparing your DNA with a panel of DNA from people with known origins (who are known as the reference panel or reference populations). The DNA company then look to see which parts of the customer’s DNA are similar to those from people represented in groups in the reference panel/populations using their own algorithms. As the companies gradually define more regions, so the ethnicity reports, over time, will become more ‘accurate’ and there are sure to be updates as the reference panels/populations are refined.

Why different companies report different estimates

As each company has its own reference groups then the ethnicity for an individual will reflect those differences. If you upload your raw data to other companies, you will see changes in your ethnicity. Percentages are likely to stay roughly accurate at the continental level, but regions are somewhat fluid.

My ‘British’ ethnicity is roughly 55% on all the sites though I am 100% European on most. I’m partly North Western European according to 23andMe, FamilyTreeDNA and MyHeritage but have Scandinavian only on FTDNA, East European only on MyHeritage and 23andMe show touches of Spanish and Native American!

About those tiny percentages

Lee’s exotic ethnicities are all less than one percent, so he is likely to see these small percentage populations ‘vanish’ or change over time. Indeed smaller ‘trace’ ethnicities, particularly of 1% or less are unreliable so are often considered as false or ‘noise’.

Check each company for the science

Clicking the ‘?’ on your DNA story will bring up a host of information on Ancestry, while 23andMe has ‘scientific details’ and ‘frequently asked questions’ tabs on the ‘Ancestry Composition’ page.

What does this mean for Lee?

To answer Lee’s question: Because each testing company has its own reference panel and algorithms, you are likely to get different ethnicity results from each company. It’s called an ethnicity estimate for a very good reason! Cousin matching is the best way for Lee to discover where his ancestor came from.

This Q&A is part of Karen Evans' ongoing DNA series in Family Tree magazine. Get your copy here.