A Segment-ology TIDBIT
We can group Matches several ways:
- Each Triangulated Group (TG) includes Matches who share the same Common Ancestor (CA). This is based on your DNA segment from an Ancestor, which other Matches also share. 23andMe, MyHeritage and GEDmatch all have tools for Triangulation.
- Clustering includes Matches who share multiple Shared Matches with each other – they tend to be based on the same Ancestor. The Leeds Method focuses on 4 groups representing our 4 grandparents. This is based on the probability that groups of Shared Matches will probably have the same Ancestor. When the lowest threshold is used (6cM), all of the company Matches are included and the Clusters tend to approximate a one-to-one relationship with TGs. This is a good tool to group our Matches at AncestryDNA and FamilyTreeDNA. I blogged about some Clustering programs here.
- We can also form Clusters based on ethnicity, geography, Haplogroups, etc., but, in general, these will not be as precise as TGs and Shared Match Clustering. These Clusters are, however, often very helpful in homing in on a CA.
Groups can help us in several ways:
- Everyone in a group should have the same objective: finding the CA. There is synergy in a group; and working together often results in a better outcome. One person’s Brick Wall or bio-Ancestor (vs. an NPE) may be in the Trees of other Matches in the Group.
- Close Cousins and their CAs with you provide a beacon toward the more distant CA, and limit the possibilities that would otherwise need to be explored.
- Once several Matches in a group agree on a CA, that CA line can be imputed to the other Matches. Many times I have searched a Match’s Tree for a specific Ancestor (highlighted in the Cluster), and found it! I’ve also communicated with Matches with no/small Trees and asked specifically about a surname and gotten positive/helpful responses.
- Use Clustering to form groups at FTDNA, MyHeritage and 23andMe, and use them as a basis for TGs – Triangulation goes much more quickly when you only compare segments that will probably Triangulate.
We can form Triangulated Groups at 23andMe, MyHeritage, GEDmatch, and, with a Clustering pre-start, at FamilyTreeDNA – but those companies, generally, do not offer much in the way of genealogy tools, and only a few of the Matches have robust Trees. On the other hand, AncestryDNA has a lot of good Trees, and great tools like ThruLines, but no DNA segment data – however, we can do Clustering. DNA and No Trees; OR Trees and NO DNA – it’s frustrating… So how can we merge the TGs and AncestryDNA’s Clusters?? More on this later…
BOTTOM LINE: We need both Triangulated Segments and Triangulated Genealogy to be in sync (reinforcing each other) before we can have confidence in our conclusions. One without the other is incomplete research.
[AQ] Segment-ology: Grouping Matches – Try It! TIDBIT by Jim Bartlett 20191128