Originally Posted by tabbey
I suspect they are being over specific with regard to local pinpointing places of origin. While work is in progress, I do not believe it can yet be narrowed down so precisely.
For genealogical companies, DNA is a potential goldmine, hence the snake oil sales tactics.
From what I've read about "Genetic Communities" feature that's supposedly coming at end of this month (or in early April) is that it's based off using people in their database to find matches in specific region.
So for example in case of Healy-Rae he most closely matched people who had already tested with origins in region that mentioned.
Obviously for most accurate results you are going to need people with at least 4 grandparents (or prefable 8 great-grandparents) from same geographic region. This is one of the criteria for the up and coming Irish DNA Atlas (Royal College of Surgeons involved). To be in that study a person had to have all 8 great-grandparents from a specific geographic region of around 30km across. I couldn't take part myself as I didn't meet the criteria.
Given the age of the participants the average great-grandparent was born in the late 1840's so it will give us an idea of genetic substructure in Ireland around the time of the Famine.