Ancestry - don't delete our DNA matches!

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Eric Weitzel
Eric Weitzel 109 Comments
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Ancestry recently announced that they will be removing all DNA matches below 8 cM from every customer's DNA match lists "in early August" of 2020. (Previously the DNA matches list only excluded below 6 cM.) This comes as they roll out a new matching algorithm.

While this may be welcome news to some (those who dislike having false positives among their matches) it is disastrous news to all those who rely on these distant matches to research their distant ancestors. Conventional research only gets one so far - the DNA side has become crucial for getting past brick walls. Now Ancestry wants to restrict our matches.

Partly, this is a cost-cutting measure. As stated in their white paper, "The first factor is data storage. Since the number of matching segments grows exponentially with decreasing length, we dramatically reduce the storage requirements of our matching database by increasing the cutoff." Ancestry has grown to 18 million customers and that means a lot of server storage. By cutting out the most distant matches from everyone's lists, estimates suggest it will cut our DNA matches lists in HALF. Source: https://www.dataminingdna.com/impact-of-ancestry-r...

The other reason provided by Ancestry is that "the accuracy ... drops rapidly with decreasing IBD length—that is, the shorter the length of the detected IBD segment (expressed in genetic distance), the less likely it is that the detected chromosome segment is truly inherited from a common ancestor." In other words, not all matches are "true" matches when you get this small. But this has ever been true - and Ancestry should continue to allow its users to work with these valuable true matches among the false positives.

Ancestry has outlined ways of preserving matches so they are not lost when this change rolls out, but it involves marking each match yourself. They provide no way to do this in bulk. With tens of thousands of matches to mark, it will be impossible to save all our data - not to mention, we'll be missing out on *future* Ancestry DNA matches we might have seen in that under-8cM range.

As Ancestry customers, we urge you, Ancestry, to reverse this decision. Do not remove our data.

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