Version 4 of the Shared cM Project has been released, utilizing over 60,000 known relationship results submitted by genealogists. The Shared cM Project was begun in 2015 by Blaine Bettinger in order to crowd-source the actual number of shared centiMorgans, cMs, of variously related people who match each through autosomal DNA testing.
Obviously, in order to contribute to the Shared cM Project and participate, you must know how you are related to your matches. You can read about the earlier versions of the project, here.
The Shared cM Project has been very useful for genealogists attempting to determine potential relationships of unknown testers, in particular, because sometimes what we “expect” to see based on academic predictions and models isn’t actually what happens.
Of course, the flip side of that is that sometimes people who contribute relationships don’t understand or report relationships accurately; specifically relationships such as “half,” and “removed.” Nonetheless, with enough data, these reporting errors become statistical outliers. You can participate by contributing your known relationship data through the portal, here.
Blaine’s blog about the new V4 version is here and the full 56-page pdf paper about the results and methodology is here. If you want to understand how the project works, not only is this paper essential reading, it’s a wonderful educational source.
By far, the most common usage of The Shared cM Project results is the interactive tool created at DNAPainter by Jonny Perl.
The Shared cM Project tools are found under the Tools and WATO tab, here.
Click on Shared cM Tool when navigating from the main DNAPainter page.
You’ll see the updated V4 relationship chart, with the field to enter the amount of shared cMs between you and a match above the chart, shown partially above.
Selecting a cM number at random, I entered 1300. The results show the probabilities of various relationships between two people who match at 1300 cMs.
1300 shared cMs can be any of the relationships shown, above. The grey, faded background relationships are not candidates at 1300 cMs, according to V4 of the Shared cM Project.
A new feature added by Jonny provides the ability to click on a relationship and view the histogram from The Shared cM Project showing the submitted relationship amounts. For aunt/uncle at 1300 cMs, 26 people reported that matching amount. The most common amount of shared DNA was 1800 for that relationship category.
You can read Jonny’s latest blog introducing these new features, here.
Thanks to all of the 60,000+ contributors, Blaine and Jonny who made this possible.
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You mentioned errors like removed or 1/2 relationships. Is there away to correct these after they were submitted?
I don’t think so, but I’m not positive. You might try asking Blaine.
There’s no way to correct it if it has already been incorporated into the project. Every submission prior to July 2019 has been incorporated.
Thank You for keeping us up to date and on the cutting edge of Genetic Genealogy. Every little bit helps in our quest for answers! Thanks to Blaine & Jonny too!!
I know I contributed some to an earlier version of the project, but I’m now realizing I have many more to add now (I have made progress after all!!) One problem I have is about the question involving the number of shared segments. With Ancestry matches, this is easy, since they tell you how many segments (although not their size), but with my matches on other sites I’m wondering how this is determined. Do I count the segments over, say, 7cM, or 5 cM, or is there another definition of segment I should know? I can’t imagine that I should be counting every small segment of 1cM, yet I assume they are included in the total cM. Sorry, I don’t seem to be able to find this information anywhere.
From what I recall, yes, you enter what the vendor reports. I think the instructions were with the submission portal.
Exactly as Roberta notes, report what the vendor reports.
Sorry, maybe I’m missing something, but I can’t find any instructions on this point on the submission portal and what the vendor reports is sometimes flexible. Bear with me— I’m sitting here in isolation in France waiting for the virus to leave my body and maybe it has addled my brain! Great excuse, anyway, if not much fun. I have my DNA at all the vendors and here is what I think I am seeing:
Ancestry just tells you what they want to tell you… so I put that down
My Heritage appears to be showing segments above 6cM
23andme seems to be giving me segments over 7cM
The default on FTDNA is segments over 5cM, but you can also choose to see segments above 1cM, 7cM or 10cM. I assume the total cM given includes all of the above, but counting the number of segments is left up to the individual — hence my confusion.
The default on GEDmatch is over 7cM, but one can also choose to go lower or higher.
I would like to be consistent, but am not sure what that means here! Since I can’t find any vendor by vendor instructions, I have tentatively decided to go with the 7cM cutoff on FTDNA and GEDmatch and leave MyHeritage at 6cM and 23andme at 7cM as presented.
If anyone (Blaine?) would like it done differently, please chime in. I’m not moving for at least another 2 weeks and will just keep compiling the results in a spreadsheet before entering them all at the end, so am open to adjusting my method if need be.
Correct, use the company or database defaults. But please only submit a particular relationship once even if they’ve both tested at multiple companies. There’s no preference for which company to use. Thank you for your submissions!!
Thanks, Blaine! Will do.
Is there a reference that can help you figure out complicated relationships for the Shared cM too?
For example, I have two relationships with a distant cousin; 3C1R and a 4C1R. Does the Shared cM Tool use both relationships in its database or is there a term that includes both of these relationships?
The problem is that DNA is passed generationally in different amounts, resulting in relationships this distant carrying different amounts of DNA, if any at all. So, no, all this tool can do for you is to bracket a relationship so you can work on it genealogically.
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