Sunday, December 7, 2014

Are The New Moderate Matches Good?

I had to correct this post again. Timber is a filter that AncestryDNA uses and could be a reason for the segment size differences? Breaking up of compound segments through phasing is another possible reason You can view an explanation of Timber here.

Some people feel the Timber system is flawed? I would like to know more about it.

Because of the possibility of a phasing error I wouldn't completely disregard moderate matches. Some of these share large segments of DNA not reflected in the phased results. There is a phasing error rate of 1 for every 100 heterozygous sites in a sample.

Since GEDmatch is now working again I decided to do some research on my AncestryDNA matches. I was curious about those Moderate about 6cM and under matches. I did some searching on my Moderate match usernames to see if I could find any to compare with. A few had uploaded to GEDmatch and I quickly discovered the cM ranges they gave for Moderate matches were way off. I found that one of these matches shared a 15 cM segment and another an 18 cM segment, while yet another shared an 8 cM segment. Why put out these estimates at all? Why not explain these are Timber filtered and phased so the results can't be compared elsewhere?

The illustrations below demonstrate the differences between the Timber filtered and phased results from AncestryDNA and the unphased, unfiltered GEDmatch and Family Tree DNA results.

The Extremely High match I found is obviously extremely good. Good call here.

Now we move to a Very High Comparison. We share a couple segments so I'd agree.
Just plain High. Ok we just have on segment so I'll go with that. It's near the range.

Now we move to Good matches which are sometimes better than High? I noticed that these Good matches also match me at Family Tree DNA and the segment sizes are basically the same there, and they declare these matches to be 2nd to 4th Cousins instead of distant.

Good Confidence match

Good Confidence match
Good confidence match
Moderate matches are all over the place cM wise. Likely range from 5 cM's to 20 cM's.
Moderate Confidence
15 cM segment Moderate Match


Jason Lee said...

Those are some wild discrepancies. Ancestry's process in which they use their Timber algorithm to "recompute the length of the segment" needs to be better explained.

Anonymous said...

Thanks for sharing this info. I toy with the idea of having someone in the US mail me an Ancestry kit. Info like this is invaluable in helping make my decision.

Annette said...

Thanks for the comments! It sounds like the Timber algorithm may cause the discrepancies in the segment sizes? I would like to know more about it too.

Jason Lee said...

I'm surprised that we've heard next to nothing about Timber. The conversation is overdue. I have a bit of information that I will be posting in the next day or two.

Annette said...

Thanks so much Jason! Look forward to seeing that! I'm very curious.

Annette said...

A link to Jason's blog