The case of the disappearing “matches”
Yes, actually The Legal Genealogist is aware that it isn’t Sunday, so it’s unusual to have a post about DNA appear in this space.
But AncestryDNA hosted an informational session with a number of genetic genealogy bloggers and educators yesterday, and there’s a major development in the works that folks who have tested with AncestryDNA need to know about — and begin to understand — as soon as possible.
Now let’s review what we’re talking about here: the AncestryDNA test is an autosomal DNA test. It looks at the kind of DNA that you inherit equally from both of your parents: you get 22 autosomes1 (plus one gender-determinative chromosome) from your father and 22 autosomes (plus one gender-determinative chromosome) from your mother, for a total of 23 pairs of chromosomes. So this is a test that works across genders to locate relatives — cousins — from all parts of your family tree.2
Ancestry was the last of the three major testing companies to get into the business of testing autosomal DNA, but it has become one of the biggest — if not the biggest — player in that market in the two years since its product launched in May 2012.
One of the things that has set AncestryDNA apart from the other testing companies was a decision to err on the side of inclusion in listing people as matches. Where both Family Tree DNA and 23andMe have fairly tight criteria for declaring two people who’ve tested to be genetic matches, AncestryDNA has had much more liberal criteria.
That has resulted in a much longer match list at AncestryDNA than you’ll find at either of the other two companies — but it’s also resulted in a lot of people being on your match list who really aren’t your genetic relatives at all. The term for those folks: false positives.
So here’s the challenge: how do you eliminate, or at least reduce, the number of false positives without creating the opposite problem — eliminating some people who really are genetic relatives? The term for those folks is false negatives and, from a research standpoint, it’s worse to lose a real match than it is to have to wade through bad ones.
AncestryDNA yesterday outlined its plan for a new matching system which it expects to roll out by the end of 2014. And it’s going to come as a big surprise to a lot of users, especially those of us who have any colonial American ancestry (and who therefore have these long match lists at AncestryDNA):
Our numbers of matches are about to drop like a rock.
And that, folks, is going to be A Good Thing.
The new matching system begins with a better, deeper, more accurate analysis of the data that helps define who is and who really isn’t genetically related.
One part of the new analysis is through the identification of some parts of our genetic code that really don’t mean anything at all. Some pieces of DNA that we once thought meant we were genetic cousins we now understand just mean we’re all human, or all Scandinavian, or all African. By taking those pieces out of the matching system, AncestryDNA will eliminate many of the false positives.
In some cases, someone who has tested with AncestryDNA may lose hundreds of matches by the better definition of the people who really fall into this false positive category. In other cases, the number may drop by thousands. In my own results, for example, AncestryDNA currently reports more than 12,000 matches. I expect the new reporting system to drop that to fewer than 1,000 matches.
The other big part of the new analysis is in the way AncestryDNA looks at the bits and pieces of our genetic code that we use for genetic genealogy testing. Since it doesn’t look at all of our DNA, but only parts of it, autosomal DNA testing relies on making some educated guesses about the parts of it the test itself doesn’t look at.
In a way, it’s like reading a book with only some of the words showing up on the page; the analysis system has to guess at what the missing words are. The better the guesses are, the better the results are. So part of the new system is a better way of thinking about what the missing words are likely to be — and in what language. If I’m 100% European, for example, the system shouldn’t conclude that the missing DNA words are in an Asian language.
Emphasizing the right missing words means the people who show up on our lists as matches will be better matches. More accurate. More likely to really be our cousins.
Now one of the things we hope for is a way to capture the lists of people who are now on our match lists (false positives and all), and especially a way to capture the lists of people who show up in our shaky leaf hint lists even if they are false positives. It’s a data set some of us may want to preserve and use in the future. The AncestryDNA representatives at yesterday’s meeting were receptive to the idea — it hasn’t been promised, but we are keeping our fingers crossed and pushing as hard as we can.
So… what does this all mean?
It means that one day in the not-too-distant-future those of us who’ve tested with AncestryDNA are going to log into our accounts, open our DNA results and the number we see on the graphic highlighted here — of pages of matches — is going to be an awful lot smaller.
Instead of 260 pages of matches, with most of them being false positives, I expect to see perhaps as few as 20 pages, with most of them being pretty darned good matches — real genetic cousins to work with and, with luck, advance our mutual understanding of our common ancestry.
Get ready. This change is coming. But this part of what AncestryDNA has planned — the smaller, or shorter, match list — is not a bad change.
This is a case where less is really more: more useful, more powerful, more accurate.
Watch this space for more info …
- “An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (the X and Y).” Glossary, Genetics Home Reference, U.S. National Library of Medicine (http://ghr.nlm.nih.gov/glossary=Glossary : accessed 6 Oct 2014), “autosome.” ↩
- See generally Judy G. Russell, “Autosomal DNA testing,” National Genealogical Society Magazine, October-December 2011, 38-43. ↩