How reliable are the TIP reports on FTDNA Y-67?

+7 votes
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My closest Y match is also a Campbell, but with no known relationship. The TIP report shows probabilities of shared ancestry of 68% within 2 generations and 90% within 4. We both took the Y-67 test. But the likelihood of shared ancestry within less than 6 generations seems remote. My male line ancestry is confirmed by au-dna back to my GG Grandfather, who immigrated from Longford, Ireland in 1842. Communication from the other test taker has not been forthcoming, but he has a convincing paper trail back to Ireland (immigrated abt. 1805), though I don’t know from which county.

The geography in the US between the families doesn’t line up. My Grandfather, G Grandfather, and GG Grandfather all travelled for their work, but it seems extraordinary for one of them to be responsible for an NPE with a geographically remote Campbell line.

Does it make more sense to consider these lines as likely to have diverged in Ireland shortly before the first group emigrated?
in Genealogy Help by B Campbell G2G2 (2.1k points)
retagged by Ellen Smith
You can modify the percentages by changing the default "Common Ancestor" if you know that there wasn't one within a certain number of generations.

This moves the likelihood further back. As an example, I have a shared match with one divergence at 111 markers. The default gives a percentage of 97% at the 5th generation, but when I change the common ancestor to 4 generations the 5th is down to 78%.

It is designed to give you an indication and obviously the lower the number of STR markers the less accurate the TIP will be.

1 Answer

+8 votes
 
Best answer
I have had a similar situation with a y-37 match which has made me question the reliability of the tip report generational percentages.  Ftdna does allow you to modify the tip report by selecting a number of generations for which no common ancestor is possible. I would try that and see how it modifies the generational percentages.  Other than that I agree with you that the most likely scenario is that your common ancestor was a Campbell in Ireland and that the tip report is overestimating the likelihood that there is a common ancestor in more recent generations.
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selected by B Campbell

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