Updated Threshold Values for Family Finder

I remind researchers in my presentations that we are still at the cutting edge of DNA technology and genetic genealogy, or the bleeding edge as my techie friends phrase it. As we learn more, we change algorithms and techniques to incorporate the new knowledge. I don't expect the advances in genetics to slow down for quite some time so, as Bette Davis said in All About Eve, "Fasten your seat belts, it's going to be a bumpy night." Although for us it won't be just a night, it will be months and years. Most of the bumps should also be major improvements, as is the one discussed below.

Experienced genetic genealogists and test-takers have been asking Family Tree DNA to modify the thresholds used to determine DNA matches in the company database.

The company delivers on those changes with this announcement.

You asked for it - we listened!

For several years the genetic genealogy community has asked for adjustments to the matching thresholds in the Family Finder autosomal test. After months of research and testing, we have implemented some exciting changes ...

Currently, the current matching thresholds - the minimum amount of shared DNA required for two people to show as a match are:

• Minimum longest block of at least 7.69 cM for 99% of testers, 5.5 cM for the other one percent
  
• Minimum 20 total shared centiMorgans
  

Some people believed those thresholds to be too restrictive, and through the years requested changes that would loosen those restrictions.

... the following changes will have been implemented to the matching program.

• No minimum shared centiMorgans, but if the cM total is less than 20, at least one segment must be 9 cM or longer.
  
• If the longest block of shared DNA is greater than 9 cM, the match will show regardless of total shared cM or the number of matching segments.
  

The entire existing database has been rerun using the new matching criteria, and all new matches have been calculated with the new thresholds. Most people will see only minor changes in their matches, mostly in the speculative range. They may lose some matches but gain others.

We're excited about this update and hope you will be, too. If you have any questions, please let me know.

Additional information was included in a message to all group administrators.

Until now the amount of shared DNA required for two people to show as a match was a minimum of 20 total centiMorgans of shared DNA with a minimum longest block of at least 7.69 cM for 99% of testers, 5.5 cM for the other one percent.

With the adjustment, if two people share a segment of 9 cM or more, they will show as a match regardless of the number of total shared cM. However, if there’s not a block that’s 9 cM or greater, the minimum of 20 shared cM with a longest block of 7.69 cM applies.

We also slightly altered other proprietary portions of the matching algorithm that will, to a small degree, affect block sizes and total shared centiMorgans. These changes should have only marginal effects, if any, on relationships, generally in the distant to remote ranges.

There’s a separate proprietary formula that is also applied to those with Ashkenazi heritage, but you can, of course, expect to have more new matches than those not of Ashkenazi heritage.

The entire existing database has been rerun using the new matching criteria, and all new matches have been calculated with the new thresholds.

Please keep in mind this change will not affect close matches, only distant and speculative ones. Some matches will fall off, others will be added. Most people will likely have a net gain of matches.

Your myOrigins results may change slightly with the rerun, but we have not updated or changed myOrigins yet. We’ll let you know when that happens.

Blaine Bettinger's post includes a flow chart illustrating the changes:

Blaine T. Bettinger, “Family Tree DNA Updates Matching Thresholds,” The Genetic Genealogist, 24 May 2016 (http://thegeneticgenealogist.com/2016/05/24/family-tree-dna-updates-matching-thresholds/).

Other bloggers who have posted about the change include:

Rebekah Canada, "Coming updates from Family Tree DNA! 25 May 2016," Haplogroup (http://www.haplogroup.org/coming-updates-from-family-tree-dna-25-may-2016/).

David R. Dowell, "More Family Finder Matches?" Dr D Digs Up Ancestor, 24 May 2016 (http://blog.ddowell.com/2016/05/more-family-finder-matches.html).

Roberta Estes, "Family Finder Matching Thresholds Changing at Family Tree DNA," DNAeXplained, 24 May 2016 (https://dna-explained.com/2016/05/24/family-finder-matching-thresholds-changing-at-family-tree-dna/).

Debbie Kennett, "New match thresholds for Family Tree DNA’s Family Finder test," Cruwys news, 24 May 2016 (http://cruwys.blogspot.co.uk/2016/05/new-match-thresholds-for-family-tree.html).

Judy G. Russell, "FTDNA changes matching system," The Legal Genealogist, 24 May 2016 (http://legalgenealogist.com/blog/2016/05/24/ftdna-changes-matching-system/).

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To cite this blog post:
Debbie Parker Wayne, "Updated Threshold Values for Family Finder," Deb's Delvings Blog, posted 26 May 2016 (http://debsdelvings.blogspot.com/ : accessed [date]).

© 2016, Debbie Parker Wayne, Certified Genealogist®, All Rights Reserved