Using Family Finder results for genealogy is more challenging for individuals of Jewish ancestry because of a lack of genealogical records, surname changes, and frequent intermarriage.
The lack of genealogical records means that finding the connection with even a third cousin may not be possible. It is important then to focus on those matches who come from the timeframe of available records.
Name changes are, as always, one of the biggest challenges of Jewish genealogy. Here is an example from Max Blankfeld, from Family Tree DNA. The following is an example from Max Blankfeld of Family Tree DNA:
I have one match predicted as 4th cousin with the last name Rubio – typical Hispanic name (I also had his first and middle Hispanic names). My first reaction was “why do I have this name here?” Well, I checked his record, and there’s a note there: his ancestral name was Rubizewsky. after checking JewishGen I saw two Rubizewsky records from a very small town in Belarus with the name Pinsk. And guess where my mother is from? Yes, you guessed it right: Pinsk!”
As a result of frequent intermarriage, a Family Finder cousin match may show a total value of centiMorgans composed from the combination of different lines. That is, they are a more distant cousin who is related in multiple ways. Max Blankfeld gives the following personal example.
I had a case of a person that matched with my nephew (my brother’s son) as a 2nd cousin, and with me as a 4th cousin. If we were talking about matching with just one line, he should be 3rd, and I 4th. Because he may be adding blocks of DNA from his maternal line (unrelated to me) to the relationship with that person. Those blocks, adding up to the my main block with him, elevates by one generation his matching to that person.
Beginning on April 21, 2011, we have modified our Family Finder matching algorithm to address this. The changes affect the match list for Ashkenazi Jews. The outcome is calculated Family Finder relationships that more accurately reflect relationships to other Ashkenazi Jews.