BLUF – The matrix which can be created by all the shared cM relationships is also showing the range of cousins who don’t Match each other.

I have now shifted to using my Common Ancestor Spreadsheet to analyze the cMs between my Matches. This spreadsheet lists about 9,000 Matches who are known cousins on specific Ancestors (a small percentage of Matches share multiple Common Ancestors with me). The backbone of this spreadsheet is a list of all my Ancestor couples out to 8C level (and some beyond), with columns for their Ahnentafel number (e.g. 16); and husband’s birth year. Under that goes a row for each Match with that Ancestor as a Common Ancestor (with the Ahnentafel number and cousinship (e.g. 3C1R) and the Match’s given names of the child and birth year the CA couple. The next two columns to the right are the Match’s Ancestor who is the grandchild of the CA, and their birth year; etc. With this setup, I can sort on Ahnentafel Number and the first birth year column and then the second birth year column and the whole spreadsheet sorts into family groups.

I am now selecting a Match and entering a * in a new column; and then, in that column, the cM of their closest Matches already in the spreadsheet. [NB: As previously reported, I’m also finding Matches who are very close relatives to the *Match (sometimes a parent or child or 1C), which causes me to go down that rabbit hole – which, in turn, frequently results in a new known cousin Match added to the spreadsheet – it’s like drinking through a fire hose.]

Anyway, as I now look down the amount of Shared cM between Matches (in a * column), I can clearly see the parents/children, siblings, aunts/uncles/nieces/nephews and close 1C and 2C in close rows of the spreadsheet. The Shared cMs get smaller and smaller up and down the spreadsheet – in fairly predictable order as the spreadsheet has different “layers” of relationships – it’s very comforting to see this pattern. Mind you, it’s not a straightforward “curve” – there is the same “jumble” that is reflected in the Shared cM Project cMs – the overlap of possible ranges among different cousinships.

The other thing that is showing up under a *Match, is that not all the 3C or 4C or 5C are showing up as Matches. This is expected. Remember the rough estimates that true 3C only match 90% of the time; and 4C only match about 50% of the time; etc.  I would need to have 9,000 columns, to perform a full analysis, and that probably isn’t in the cards. Perhaps one of the 3rd party programmers can come up with a automated program to do this… 

Bottom line: for now, it appears the concept of “true cousins don’t always match each other” is alive and well in the Shared cM data…

[22CL] Segment-ology: ProTools Part 3 TIDBIT; by Jim Bartlett 20240705