Wednesday, July 5, 2017

PD Index for Jewish Ancestry--Some Wrinkles

I'm a geek.  And as a genealogist, genetic genealogy plays right into that--I can use my math and science background to leverage another tool to better understand my family's history.  The more relatives who have tested, the better fidelity I can get in understanding which DNA came from which ancestors which can then help me identify other relatives via DNA.  In doing this, I have tested a lot of cousins (around 50), and I'm still going--I just sent in 3 kits this week, and another relative is hopefully shipping his back directly right around now.
Some of my kits on GedMatch.  Yes, there are a lot.

People get excited when they see they match 5 (or 10 or 25) of my kits--but often they're kits from relatives on various branches of my family.  So while these matches are related to me, they're not related to one another.  Because endogamy means that Jews tend to get a LOT of matches, pretty much anyone with Jewish ancestry will match at least one (and probably multiple) of my kits.  I get excited by those who share large segments or who match multiple cousins who themselves share common ancestors.

So while matching several of my kits generally isn't so exciting in terms of finding a relationship, Louis Kessler noted that individuals who match myself and Israel Pickholtz (who has even more of a DNA addiction than I) can use that fact to confirm Jewish ancestry.  He introduces the Pickholtz-Diamond Index of DNA Ashkenazi Jewishness (PD Index) which gives a measure of how many Pickholtz & Diamond matches an individual has.

My internal geek has been ruminating over the various complexities of such an index (even if the name made me giggle when I saw it when I woke up this morning).  If this really gets used, there are a few issues that would need to be addressed.
  1. One's PD Index can periodically change as either Israel or I test new relatives.
  2. Some of my relatives are not 100% Ashkenazic Jewish--so how would we know if the connection is via their Ashkenazic DNA or the DNA from another ancestral line?  I know some of Israel's relatives also do not have 100% Jewish ancestry as well.  (Also, I administer a kit for a friend who has no Jewish DNA whatsoever.  So drawing conclusions of Jewish ancestry for matching her kit would be very incorrect.)
  3. Israel and I have ancestry solidly in Eastern Europe for at least the past few centuries.  Is there a Sephardic genetic genealogist who has similarly tested many relatives?  How about someone with strong German or French ancestry?  We'd need to have a good representation of Jewish communities from around the world to make this truly useful to everyone.
Anyone have other issues that would need to be addressed?  Please comment below.  And let me know what your PD Index is under the current construct.  (And if you see really large segments, definitely let me know--that would be worth investigating further!)

Note:  I'm on Twitter.  Follow me (@larasgenealogy).


  1. 1. Nothing really wrong with that.

    2. In essence, we are doing exactly what they do to pick people for the admixture studies. We are trying to find 100% Ashkenazi people. So the non 100% need to be removed somehow. It's those sorts of inaccuracies that cause the DNA company's ethnicity estimates to be off, and is the reason why I'm 1% Eskimo at MyHeritageDNA.

    3. Who else do you know who's done 50 or more tests? You two are the gold standard for ability to convince relatives to test.

    1. Thank you for the kind words, Louis.

    2. You actually match me on gedmatch and familytree dna. I actually did the test first on ancestrydna then I took the test again on 23&Me. My haplogroup on the material side is K1a1b1a. I belive we are between 5th to remote cousins according to familytree dna. Do you by any chance have Katz or Cohen in your line.

  2. There's a fortune to be made here, somehow! ;-)

    I checked the matches of my sisters and me to any kits administered by Israel Pickholtz (P) or Lara Diamond (D), and came up with the following count:

    Me: 8 (P), 8 (D), including Lara herself
    Sister 1: 12 (P), 3 (D)
    Sister 2: 19 (P), including Israel himself, 4 (D)

    Note that Sister 2 is my half-sister; her grandfather on the other side was from Krakow, so that's probably her Galician connection. Sister 1 and I have no known connection to that region.

  3. There's a fortune to be made here, somehow! ;-)

    I checked my results, and those of my sister and half-sister, for matches with people whose kits are administered by Israel (P) or Lara (D). My findings:

    I match 8 (P) and 8 (D), including Lara, herself.

    Sister 1 matches 12 (P) and 3 (D)

    Sister 2 matches 19 (P), including Israel, himself, and 4 (D)

    Note that Sister 2, my half-sister, is 99% Ashkenazi (Sister 1 and I are a few points less), and her grandfather on the other side is from Krakow, so that's probably how she connects with Israel's Galician ancestors. Sister 1 and I have no known Galician ancestry, but I figure that our ancestors traveled through the region on the way to Ukraine, a few centuries ago, and some family members branched off as they migrated.

  4. I match 27 of Israel's kits and 6 of Lara's on GEDmatch. I am not sure how to search on FTDNA for matches by email address. But I guess I made the cut on GEDmatch. Not that I had any doubt about my Ashkenazi background!

  5. I am just new to this and just considering getting a DNA test. What service do you recommend I use -- FTDNA or other? Thanks!

    1. I prefer FTDNA. You can also test with Ancestry and upload resulting raw data to FTDNA and GedMatch.

  6. Thanks much! I enjoy your blog.

  7. I have 8 Pickholz matches, longest 13.3cM
    I have 16 Diamond matches, longest 14.0
    This gives a Pickholz-Diamond Index of 12...

  8. I found my wife's kit shows (16+7)/2 = 11
    However if we change the sort order to Largest cM, it's (17+3)/2 = 10
    Longest match is 24.9 (israelp) and 16.4 (laradiamond)

  9. I've recently found out about my Jewish ancestry. Think it goes back to my great-grandfather. My PD index comes out to 4.5 with the longest segment 16.5. Does that seem to coincide? Thanks!!

    1. It's hard to tell. That definitely implies some Jewish ancestry, but this doesn't show how much Jewish ancestry one would have.

    2. I should have told you that both my brothers and I tested - on 23andMe and Ancestry - with between 21% and 30% Ashkenazi. Also, while we're at it, my cousin wants to test. What company do you recommend? Thank you so much!!

  10. On FTDNA, I match to about 20 each of P and D, and my brother matches to 24 and 25. Our predicted Ashkenazi percentage on several sites is between 85 and 90%. Sadly, no significant matches to your relatives.