Announcement

Collapse
No announcement yet.

Major discrepancy with Ancestry DNA

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Major discrepancy with Ancestry DNA

    A new match burst into second place on my FTDNA Family Finder matches this week. We share 83cM.

    I didn't recognise anything about this person, and I went back to Ancestry (where my tree is much more complete) to do some research. While doing this, I realised that I had a match with a person of the same name in Ancestry, but at a much lower level: 12cM. I have emailed her, and she has confirmed that they are the same person.

    I'm really quite surprised about this. I understand that the tests and the comparisons are different, and I have several other matches who appear in both systems and with different degrees of matching, but not to this extent.

    My kit on FTDNA is an import of my Ancestry data, not an authentic FTDNA kit. I don't know about my matches' kit.

    I'm interested in any thoughts and explanations you may have about this, please.
    Last edited by monxton; 15 July 2020, 08:55 AM.

  • #2
    Check the chromosome browser in FTDNA, you likely have a lot of < 7cM segments that aren't typically very meaningful for IBD (Identical by descent) matching. Ancestry DNA won't typically count those but FTDNA counts them all.

    Comment


    • #3
      Thank you. Yes, that is indeed the case, there is only one match greater than 7cM ... but that one match is 22cM which is only a little less than twice as long as Ancestry is reporting, so that still seems odd.

      Is there a good source to read more about these different matching strategies?

      Comment


      • #4
        Ancestry has their "Timber" algorithm, tends to be more conservative than others, which might explain the 12cM to 22cM discrepancy.

        Here's a white paper on how they do matching.

        https://www.ancestry.com/corporate/s...hite-Paper.pdf

        Comment


        • #5
          https://cruwys.blogspot.com/2020/07/...s+(Cruwys+news)

          Update to AncestryDNA's matching system and database form Cruwys News as of yesterday.

          I have saved 150 tree matches there with only 6 cMs, so will be losing matches in the future.

          Comment


          • #6
            It would be useful to see what the free, independent GEDmatch site, where you can tweak the match parameters such as SNP counts etc., shows for this match. The discrepancy between the figures reported by Ancestry and FTDNA is far larger than anything I have ever encountered. Inquiring minds want to know, how did that happen?

            Comment


            • #7
              Originally posted by Biblioteque View Post
              https://cruwys.blogspot.com/2020/07/...s+(Cruwys+news)

              Update to AncestryDNA's matching system and database form Cruwys News as of yesterday.

              I have saved 150 tree matches there with only 6 cMs, so will be losing matches in the future.
              Roberta Estes posted today on this situation: "Ancestry to Remove DNA Matches Soon – Preservation Strategies with Detailed Instructions." She gives several strategies for keeping matches with smaller segments.

              Comment


              • #8
                https://www.ancestrycdn.com/support/...whitepaper.pdf

                Ancestry explains !!




                Comment


                • #9
                  Originally posted by betadams View Post
                  They don't really, because that paper is virtually identical to the 2016 version posted by GregK above (https://forums.familytreedna.com/for...538#post328538), except in section 3 6cM has been changed to 8cM to reflect the new policy, but without further explanation. Or did I miss some other change?

                  Comment

                  Working...
                  X