That would be because 37% of the markers they tested have their roots in Ireland.....or have been predominantly found in those of certain Irish heritage. It's an inexact science at the moment.
do they only do the one test? There are different sorts available that dig to different depths - I had a short-focus one that revealed ancestors in three continents in the last couple of hundred years, which was very interesting; my OH had one that threw up Neanderthal and Denisovan DNA, which was extremely interesting except I don't really know what you could do with it..
I`m not sure how comprehensive the Ancestry test is. I know that there used to be tests that tested the mitrochondrial DNA and they could only test what had been passed down through the female line and the male line. I have the impression that the Ancestry test has managed to merge the two
I had it done as trying to trace an ancestor born in Egypt but I didn't know if he had Egyptian parentage or born to British parents in Egypt.
It came back that I'm 45% British 23% Europe west 13% European Jewish 11% Irish 4% Iberian and 3% Scandinavian.
Not an Egyptian in sight!
I found a fairly close relation and they gave me lots of information on my family history. If someone has had the test and has a similar DNA they send you their name through Ancestry. I didn't think it was too expensive - £89, but then I'm interested in it. Others would choose to spend their money in a different way I expect.