Ancestry shared matches are those that you have in common with another match. This is sometimes referred to as ICW, an abbreviation of “In Common With”. Users of AncestryDNA can see shared matches by clicking on a particular Dna Match and looking at the Shared tab.
It’s important to know that the list on the Shared tab page is restricted to Ancestry’s chosen CM threshold. The way they put it is that they only show you “fourth-cousins-and-closer”. That translates into above 20 cM.
A Brief History
AncestryDNA rolled out their Shared Match tool in August 2015. It’s interesting to read the comments from their launch post back then, that there was some immediate confusion that still crops up on message boards.
"Wondering why Cousin A has shared match Cousin B, but Cousin B does not show shared match Cousin A."
"I am confused as to how a match for me A also matches B but B does not match A."
Why are my Shared Matches not showing?
So this has been a common question for new Ancestry users since day one of the matching service. Here is a concrete example: as I write this, the Shared Match list of my first cousin Margaret shows five matches we have in common. I happen to know that there are another 29 Ancestry matches that list Margaret on their shared match page with me.
Take Claire, for example. If I scroll down to my “distant” cousins and open Claire F, I see that we share three matches in common. But wait! There is my close cousin Margaret at the top of Claire’s list. While Claire is nowhere to be seen on Margaret’s shared list.
This is all about the threshold that Ancestry applies when displaying shared matches i.e. the threshold of “fourth-cousins-and-closer”. Claire shares 19 cM with me, and is therefore in Ancestry’s “distant cousin” category. That stops her from showing up on Margaret’s list. But Margaret is my close cousin and above the threshold, so she shows up on Claire’s displayed list.
I think of these below-threshold shared matches as “hidden” shared matches. My cousin Margaret has 29 hidden shared matches with me. Yes, that is all the way down to the low-confidence levels of 6 and 7 centimorgans. Yet Claire at 19 cM is just outside the Ancestry threshold, and there are another two at 15 cM are above. If I choose to research matches at 10 cM and above, then there are 17 other shared matches I’d like to review.
Why this threshold?
I don’t really have an answer to that question, nor can I link to a definitive answer from Ancestry. It must partly be related to avoiding false shared matches. Be aware that the lower the number of centimorgans you share with a match, the higher the chance that a match is is not really your genetic relative. This is due to the inherent random nature of genetic inheritance.
However, that doesn’t quite square with the fact that Ancestry lists your matches down to 6.0 cM. Why add restrictions with one set of data and not the other?
I don’t know.
Does this happen a lot?
The answer is yes. Take a look at the numbers in this spreadsheet of my top six matches (the match names have been altered for privacy, but everything else is real).
You can see that some matches have a *lot* more hidden shareds than are visible on their match page, while others have less. My 6th match, Connie L, has none at all.
Want to get spreadsheets with those hidden shared matches?
We offer a service that provides spreadsheets of Ancestry matches and shared matches. Click here for more info.