Sunday, 27 August 2017

Shared cM Project Update

Once again the genetic genealogy community is indebted to Blaine Bettinger​ who has updated and compiled yet more detailed statistics on total shared cM data, now more than 25,000 known relationships for autosomal DNA matches.  The study is detailed in the pdf at The Shared cM Project – Version 3.0 (August 2017).
The article includes a step by step guide to establish what a relationship might most likely be based on a particular cM match. Distribution histograms indicate the range and likelihood of various relationships for a given cM match.

The combined statistics are dominated by AncestryDNA tests, especially for the more distant relationships.

Blaine's statistics also show the effect of endogamy. For example for 3rd cousins in non-endogamous situations the median shared is 63cM whereas for endogamous situations it is 101cM.

Generally AncestryDNA shows fewer cM matching for a given relationship than the other companies. That could be owing to the company Timber algorithm which down-rates matching in pile up regions. FTDNA show more cM shared than the other companies for 2nd cousin and more distant relationships. That could be the company including more small segment matches, or than their clients have more endogamous relationships.

1 comment:

Anonymous said...

I recently had a match of 114cM's on Ancestry. Using info from three sources, I am now sure the person is a 3rd cousin. I do know also, from background research that endogamy is at play here. So, this makes sense!