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FTDNA kits match on Gedmatch but not here?

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  • sfrank
    replied
    I actually see the opposite of what madman described. For the people I know on both FamilySearch and Gedmatch, I see lower cM totals on Gedmatch. For example, using the default for one-to-one match on gedmatch (500 SNPs, 3 cM) I have three people that come in slightly under the FTDNA totals when I look them up on Gedmatch. So I don't think the analysis methods should be so dissimilar as to cause a total shared 40-50cM match on gedmatch to not register on FTDNA.

    What exactly are the minimum thresholds for cM lenth, SNPs, etc for a match on FTDNA? Is there somewhere in the faq I can read some basics about the matching alogrithm?

    Leave a comment:


  • hansonrf
    replied
    GedMatch, as they compare between different testers and datasets, is more forgiving of no-calls within the data and places where the different datasets may look at different SNPs.

    To truly answer your question would require both data files and knowledge of both GedMatch and FTDNA algorithms; Not likely to happen but I'll check back regularly...

    Bob H.

    Originally posted by madman View Post
    Those gedmatch totals were at a Total of segments of 5 cM or more so if it was set at 1 cm the total would of been way higher.

    Leave a comment:


  • S9 H9
    replied
    Originally posted by Rebekah Canada View Post
    Hi,

    I think in most cases it is the rule for the second largest block that causes matches to be dropped. We really need phasing to sort out many of the true IBS cases so that we can re-evaluate matching. It will happen this year.
    Am I understanding you correctly, that FTDNA will phase autosomal SNP files?

    If so, are you going to implement a BEAGLE-like approach? Will you require a parent to be tested also?

    Leave a comment:


  • madman
    replied
    I didn't use the SNP analysis utilities it was One-to-many matches


    Originally posted by Rebekah Canada View Post
    Hi,

    How have you set the SNPs per block level?

    Leave a comment:


  • Rebekah Canada
    replied
    Hi,

    How have you set the SNPs per block level?
    Originally posted by madman View Post
    Those gedmatch totals were at a Total of segments of 5 cM or more so if it was set at 1 cm the total would of been way higher.

    Leave a comment:


  • madman
    replied
    Those gedmatch totals were at a Total of segments of 5 cM or more so if it was set at 1 cm the total would of been way higher.

    Originally posted by madman View Post
    gedmatch cm is way different then here.


    ftdna match 20cm

    gedmatch same match 60cm


    another one

    ftdna match 20cm

    gedmatch same match 45cm

    Leave a comment:


  • madman
    replied
    gedmatch cm is way different then here.


    ftdna match 20cm

    gedmatch same match 60cm


    another one

    ftdna match 20cm

    gedmatch same match 45cm



    Originally posted by sfrank View Post
    As an example, total shared for one was 48.8, longest segment 11.1. It seem like it would meet the threshold. And that's at default settings. If I lower gedmatch to 1cM on one to one comparison, it comes up as 98.3cM. Not sure where FTDNA puts its cutoff, but either way, should be a match.
    Last edited by madman; 25 February 2014, 08:41 PM.

    Leave a comment:


  • sfrank
    replied
    Originally posted by AFBLUE View Post
    It could be that your total shared cM is less than FTDNA's threshold of 20cM.

    For example if you shared a single 19cM strand with another individual, it would show up on gedmatch as possibly a 4th cousin, but it wouldn't show up on FTDNA.
    As an example, total shared for one was 48.8, longest segment 11.1. It seem like it would meet the threshold. And that's at default settings. If I lower gedmatch to 1cM on one to one comparison, it comes up as 98.3cM. Not sure where FTDNA puts its cutoff, but either way, should be a match.

    Leave a comment:


  • Rebekah Canada
    replied
    The Matching Rules

    Hi,

    I think in most cases it is the rule for the second largest block that causes matches to be dropped. We really need phasing to sort out many of the true IBS cases so that we can re-evaluate matching. It will happen this year.
    Originally posted by Earl Davis View Post
    Does anyone understand Family Tree DNA’s rationale for this? It’s something I have ever really understood.

    I can understand to some degree them not showing say an 8cm largest with not other segments as probably being an IDS match but I don’t understand why they don’t (if this is true) for example show a 14cm largest with additional 2cm and 3cm segments and 19cm total.

    Earl.

    Leave a comment:


  • Earl Davis
    replied
    Does anyone understand Family Tree DNA’s rationale for this? It’s something I have ever really understood.

    I can understand to some degree them not showing say an 8cm largest with not other segments as probably being an IDS match but I don’t understand why they don’t (if this is true) for example show a 14cm largest with additional 2cm and 3cm segments and 19cm total.

    Earl.

    Leave a comment:


  • MitchellSince1893
    replied
    It could be that your total shared cM is less than FTDNA's threshold of 20cM.

    For example if you shared a single 19cM strand with another individual, it would show up on gedmatch as possibly a 4th cousin, but it wouldn't show up on FTDNA.

    Leave a comment:


  • sfrank
    started a topic FTDNA kits match on Gedmatch but not here?

    FTDNA kits match on Gedmatch but not here?

    I put my kit on GEDMatch and found a lot of FTDNA kits that were relatively strong matches (3rd and 4th cousins) but did not show up on my matches on FTDNA. Has anyone else experienced this? Its frustrating to know there are relatives out there on FTDNA, who have matching people in their Gedcoms, but I can't see them because for whatever reason the algorithm didn't put them in my match list.
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