Are Ancestry DNA relationship predictions accurate?

Question

I have noticed that the one line Ancestry DNA relationship estimates (e.g. 3-4 cousin) are reasonably accurate. But when I click on the explanation of the centimorgan count, the more detailed predictions don't match what I have found in historical records. For example, if I take 6 of my known 4th cousins who are in my shared matches, they appear as 3-4 cousins, but also with > 97% probability of being 3 cousins or closer. Does anyone else see this?

Answer 1

It depends. I would check the shared cM project or build a tree down to your match to find out for sure. Some Ancestry DNA relationship predictions are accurate.

Answer 2

Here are a couple of links to discussions of that question.

https://www.wikitree.com/g2g/1007791/version-4-0-of-the-shared-cm-project-is-now-available

https://dna-explained.com/2020/03/27/the-shared-cm-project-version-4-released/

There are plenty more I don't have at hand right now.  The short answer, in my opinion, is that after around the second cousin relationship, match strengths can be all over the place.  As I've noted elsewhere, my own third cousins match me anywhere from 0 cM to over 200.

Answer 3

Anecdotally, yes. It has correctly matched me with two known first cousins, and as first-second cousin (ie, first cousin once removed) with the daughter of one of those first cousins. And interestingly, it discovered a first cousin once removed that no one in the family had never known about. (verified because of the family names that she knew about - although distorted.) I knew the first cousin who was her mother (more than 10 years older than I am), who already had given up one child to adoption. So yes, in my case, it has been informative and accurate.

Comments

But those are very close relations, Jim.  How accurate are the third and fourth cousin predictions for you?

Answer 4

AncestryDNA seems to err on the side of caution when it comes to predicting relationships. My first cousin is predicted as my second cousin on there (and no, our mothers aren't half-sisters. His mother matches me as a regular full aunt). He and I share 645 cM, which is on the lower side for first cousins but still well within the range (the extreme low end for first cousins is 396 cM).

Answer 5

When I was looking for my great-grandmother, I made a chart in a spreadsheet that listed all my matches to her line with their Ancestry cMs and then changed the color of all the half-relatives, and everything matched up perfectly with my great-grandmother and Blaine Bettinger's chart.  For example, a direct descendant of my great-grandmother by her first husband is my half-cousin a few times removed.  In the chart I made, that's exactly where he showed up.