There is a somewhat widely known problem with the 23andMe ancestry estimation techniques for Koreans. It turns out, that the company's own data confirms this fact.
The Company has a chart measuring precision and recall for each ethnic category. Precision is the likelihood that a particular genetic unit estimated to be from someone of a particular ethnicity really is from a person of that ethnicity. Recall is the likelihood that a gene from a person of a particular ethnicity is accurately classified as such. Here is the breakdown (with poor performance noted in bold):
|POPULATION||PRECISION (%)||RECALL (%)|
|Central & South African||100||89|
|East Asian & Native American||99||99|
|British & Irish||90||39|
|French & German||78||8|
|Middle Eastern & North African||95||83|
Koreans are known to be often misclassified and sure enough, the numbers are bad. Only French and German rates lower than Korean by predictive accuracy. There are less accurate recall rates than those for Koreans, but 62% is nothing to write home about and it is far less accurate than for other East Asian ancestries.
There are also known problems with Southern and Eastern Europeans, all of whom have very low recall rates. Among Northern Europeans, only Finnish people really stand out as distinct.