Admixture or ethnicity estimates are described as the most widely advertised and least reliable aspect of genealogical DNA testing in various books and web references that I've seen.
ISOGG state that most providers "use a shared subset of the up to 0.7 million SNPs provided by Family Finder, AncestryDNA, 23andMe, etc. These are compared with publicly available datasets and the companies' own proprietary datasets. As can be seen from the Autosomal DNA testing comparison chart the accuracy and sophistication vary greatly and have not yet reached the quality desired for accurate genetic genealogy research".
They rate both Ancestry and MH as 5 out of 10 overall for admixture results, with the estimates for British populations rated "generally poor" for both companies. Living DNA have the highest score for British populations, rated 9 out of 10. LDNA quote my recent admixture (the last 1500 years) as being 96.4% from Great Britain and Ireland, with roughly 28% Central England, 18% SE England and 17% S Central England and about 16% a mix of NW England and N. Wales. With my grandparents ancestors over the last 200 years or so being from the Midlands, Kent and Essex, Somerset and Montgomeryshire into the W. Midlands and Lancashire, I guess you could say that's a reasonable fit, but I wouldn't take any of it as being sophisticated or precise enough to confirm or disprove more traditional research, or autosomal matching, and even they aren't committing to individual counties. GEDmatch using the same DNA data tell me that I'm of around 50% North Atlantic, 25% Baltic and 14% Western Mediterranean descent.
It's interesting, but nothing I'd rely on for researching my recent ancestors.
